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Class 11 Biology

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Class 11 Biology Video Lectures

  • Unit 1 – Chapter 1 – The Living World Lecture 1
    40:49
  • Unit 1 – Chapter 1- The Living World Lecture 2
    31:11
  • Unit 1- Chapter 1 – The Living World Lecture 3
    31:07
  • Unit 1 – Chapter 1- The Living World Lecture 4
    31:49
  • Unit 1- Chapter 1- The Living World Lecture 5
    00:00
  • Unit 1- Chapter 1- The Living World Lecture 6
    32:41
  • Class 11: Chapter 2:Biological Classification Ridib1
    00:00
  • Class 11: Chapter 2:Biological Classification Ridib 2
    00:00
  • Class 11: Chapter 2: Biological Classification Ridib 3
    00:00
  • Class 11: Chapter 2: Biological classification Ridib 4
    00:00
  • Class 11: Chapter 2: Biological Classification by Ridib Sir Lecture 5
    00:00
  • Class 11: Chapter 2: Biological Classification by Ridib Sir Lecture 6
    00:00
  • Class 11: Chapter 2: Biological Classification by Ridib Sir Lecture 7
    00:00
  • Class 11: Chapter 2: Biological Classification by Ridib Sir Lecture 8
    00:00
  • Class 11: Chapter 2: Biological Classification by Ridib Sir Lecture 9
    00:00
  • Class 11: Chapter 2: Biological Classification by Ridib Sir Lecture 10
    00:00
  • Class 11: Chapter 2: Biological Classification by Ridib Sir Lecture 11
    00:00
  • Class 11 Ch 3 :Plant Kingdom by Ridib sir Part 1
    00:00
  • Class 11 Ch 3: Plant Kingdom by Ridib sir Part 2
    00:00
  • Class 11 Ch 3 :Plant Kingdomby Ridib sir Part 3
    00:00
  • Class 11 Ch 3: Plant Kingdom by Ridib sir Part 4
    00:00
  • Class 11 Ch 3: Plant Kingdom by Ridib sir Part 5
    00:00
  • Class 11 Ch 3 :Plant Kingdom by Ridib sir Part 6
    00:00
  • Class 11 Ch 3: Plant Kingdom by Ridib sir Part 7
    00:00
  • Class 11 Ch 3 : Plant Kingdom by Ridib sir Part 8
    00:00
  • Class 11 Ch 3: Plant Kingdom by Ridib sir Part 9
    00:00
  • Class 11 Ch 3 :Plant Kingdom by Ridib sir Part 10
    00:00
  • Class 11 Ch 3 :Plant Kingdom by Ridib sir Part 11
    00:00
  • Class11 Ch3: Plant Kingdom by Ridib sir Part 12
    00:00
  • Class 11 Ch 3: Plant Kingdom by Ridib sir Part 13
    00:00
  • Class 11 Ch4 :The Animal Kingdom by Snigdha Ma’am Part 1
    00:00
  • Class 11 Ch4 : The Animal Kingdom by Snigdha Ma’am Part 2
    00:00
  • Class 11 Ch4 :The Animal Kingdom by Snigdha Ma’am Part 3
    00:00
  • Class 11 Ch4: The Animal Kingdom by Snigdha Ma’am Part 4
    00:00
  • Class 11 Chapter 4: The Animal Kingdom by Snigdha Maam Part 5
    00:00
  • Class 11 Chapter 4 :The Animal Kingdom by Snigdha Ma’am Part 6
    00:00
  • Class 11 Ch5 :Morphology of flowering plants by Ridib Sir 1
    00:00
  • Class 11 Ch5 :Morphology of flowering plants, by Ridib Sir 2
    00:00
  • Class 11 Ch5 : Morphology of flowering plants by Ridib Sir 3
    00:00
  • Class 11 Ch5: Morphology of flowering plants by Ridib Sir 4
    00:00
  • Class 11 Ch5 : Morphology of flowering plants by Ridib Sir 5
    00:00
  • Class 11 Ch5 : Morphology of flowering plants by Ridib Sir 6
    00:00
  • Class 11 Chp7: Structural Organisation in Animals by Snigdha ma’am Part 1
    00:00
  • Class 11 Chp7 : Structural Organisation in Animals by Snigdha ma’am Part 2
    00:00
  • Class 11 Chp7 : Structural Organisation in Animals by Snigdha ma’am Part 3
    00:00
  • Class11 Ch7 :Structural Organisation in Animals, by Snigdha maam Part 4
    00:00
  • Class11 Ch7 : Structural Organisation in Animals by Snigdha maam Part 5
    00:00
  • Class 11 Chp7: Structural Organisation in Animals by Snigdha maam Part 6
    00:00
  • Class 11: Chapter 8 :Cell the Unit of Life by Ridib Sir Lecture 1
    00:00
  • Class 11: Chapter 8: Cell: the Unit of Life By Ridib Sir Lecture 2
    00:00
  • Class 11: Chapter 8 :Cell the Unit of Life by Ridib Sir Lecture 3
    00:00
  • class 11: Chapter 8: Cell the Unit of Life by Ridib Sir Part 4
    00:00
  • Class 11 Chapter 8 Cell the unit of life by Ridib sir Part 5
    00:00
  • Class 11 Chapter 8 Cell the Unit of Life by Ridib Sir part 6
    00:00
  • Class 11: Chapter 8: Cell the Unit of Life by Ridib Sir part 7
    00:00
  • Class 11 chapter 8 Cell the unit of life by Ridib sir part 8
    00:00
  • Class 11 Chapter9: Biomolecules by Snigdha Ma’am part 1
    00:00
  • Class 11 Chapter9 :Biomolecules by Snigdha Ma’am part 2
    00:00
  • Class 11 Chapter9: Biomolecules by Snigdha Ma’am part 3
    00:00
  • Class 11 Chapter9: Biomolecules by Snigdha Ma’am part 4
    00:00
  • Class 11 Chapter10: Cell cycle and cell division by Snigdha Ma’am 1
    00:00
  • Class 11 Chapter10 :Cell cycle and cell division by Snigdha Ma’am part 2
    00:00
  • Class 11 Chapter 10 :Cell cycle and cell division by Snigdha Ma’am part 3
    00:00
  • Class11 Chp11: Photosynthesis,by Snigdha Ma’am Part 1
    00:00
  • Class11 Chp11: Photosynthesis by Snigdha Ma’am Part 2
    00:00
  • Class11 Chp11: Photosynthesis by Snigdha Ma’am Part 3
    00:00
  • Class 11: Chapter 11: Transport in Plants by Ridib Sir Lecture 1
    00:00
  • Class 11: Chapter 11: Transport in Plants by Ridib Sir Lecture 2
    00:00
  • Class 11: Chapter 11: Transport in Plants by Ridib Sir Lecture 3
    00:00
  • Class 11: Chapter 11: Transport in Plants by Ridib Sir Lecture 4
    00:00
  • Class 11 Ch12: Respiration in plants by Snigdha ma’am Part1
    00:00
  • Class 11 Ch12: Respiration in plants by Snigdha ma’am Part2
    00:00
  • Class 11 Ch12: Respiration in plants by Snigdha ma’am Part3
    00:00
  • Class 11 Ch12: Respiration in plants by Snigdha ma’am Part4
    00:00
  • Class11 Chp13: Plant Growth and Development, by Snigdha Ma’am Part 1
    00:00
  • Class11 Chp13: Plant Growth and Development by Snigdha Ma’am Part 2
    00:00
  • Class11 Chp13 :Plant Growth and Development by Snigdha Ma’am Part 3
    00:00
  • Class11 Chp13 :Plant Growth and Development,by Snigdha 4
    00:00
  • Class11 Chp14: Breathing and Exchange of Gases,by Snigdha ma’am Part1
    00:00
  • Class11 Ch14: Breathing and Exchange of Gases, by Snigdha ma’am2
    00:00
  • Class 11 Chp14: Breathing and Exchange of Gases,by Snigdha ma’am Part 3
    00:00
  • Class 11 Chp14: Breathing and Exchange of Gases by Snigdha ma’am Part 4
    00:00
  • Class 11 Chapter15: Body fluids and circulation by Snigdha 1
    00:00
  • Class 11 Chapter15: Body fluids and circulation by Snigdha Ma’am 2
    00:00
  • Class11 Chp-15 :Body fluids and circulation by Snigdha Ma’am 3
    00:00
  • Class 11 Chapter15: Body fluids and circulation by Snigdha Ma’am part 4
    00:00
  • Class 11 Chapter15 :Body fluids and circulation by Snigdha Ma’am part 5
    00:00
  • Class 11 Chapter16: Excretory products and their elemination by Snigdha Ma’am part 1
    00:00
  • Class 11 Chapter16: Excretory products and their elemination, by Snigdha Ma’am part 2
    00:00
  • Class 11 Ch 17: Locomotion and movement by Snigdha Ma’am Part 1
    00:00
  • Class 11 Ch 17: Locomotion and movement, by Snigdha Ma’am Part 2
    00:00
  • Class 11 Ch 17: Locomotion and movement, by Snigdha Ma’am Part 3
    00:00
  • Class 11 Ch 17: Locomotion and movement by Snigdha Ma’am Part 4
    00:00
  • Class 11 Ch 18: Neural control and coordination Snigdha ma’am 1
    00:00
  • Class 11 Ch 18: Neural control and coordination, Snigdha ma’am Part 2
    00:00
  • Class 11 Ch 18 :Neural control and coordination by Snigdha ma’am Part 3
    00:00
  • Class 11 Ch 18: Neural control and coordination Snigdha ma’am Part 4
    00:00
  • Class 11 Ch 18: Neural control and coordination snigdha ma’am Part 5
    00:00
  • Class11 Ch 19:Chemical Coordination and integration by Snigdha ma’am 1
    00:00
  • Class 11 Ch 19: Chemical Coordination and integration by Snigdha ma’am 2
    00:00
  • Class 11 Chp 19: Chemical Coordination and Integration, by Snigdha mam part 3
    00:00
  • Class 11 Ch 16: Digestion and Absorption by Snigdha Ma’am part 1
    00:00
  • Class 11 Ch 16 :Digestion and Absorption by Snigdha Ma’am part 2
    00:00
  • Class 11 Ch 16: Digestion and Absorption by Snigdha Ma’am Part 3
    00:00
  • Class 11 Ch 16: Digestion and Absorption by Snigdha Ma’am Part 4
    00:00
  • Class 11 Ch 16: Digestion and Absorption by Snigdha Ma’am part 5
    00:00
  • Class 11 Ch 16: Digestion and Absorption by Snigdha Ma’am part 6
    00:00
  • Class 11 Ch 16 :Digestion and Absorption by Snigdha Ma’am Part 7
    00:00
  • Class 11 Ch 16: Digestion and Absorption by Snigdha Ma’am Part 8
    00:00
  • Class 11 Biology Ch 12 Mineral Nutrition, Essential mineral nutrients Snigdha ma’am Part 1
    00:00
  • Class 11 Biology Ch 12 Mineral Nutrition, Deficiency of symptoms of nutrients Snigdha ma’am Part 2
    00:00
  • Class 11 Biology Ch 12 Mineral Nutrition, Mechanism of fixing Nitrogen Snigdha ma’am Part 3
    00:00
  • Class 11 Biology Ch 12 Mineral Nutrition, Nitrogen fixing bacteria Snigdha ma’am Part 4
    00:00

NCERT Class 11 Biology Chapter 1: The Living World – Diversity in the living world
### Exam Notes: Class 11 Biology - Chapter 1: The Living World **Topic: Diversity in the Living World** #### Key Points: 1. **Biodiversity:** - Biodiversity refers to the variability among living organisms from all sources including terrestrial, marine, and other aquatic ecosystems and the ecological complexes of which they are part. - It encompasses the diversity within species (genetic diversity), between species, and of ecosystems. 2. **Levels of Biodiversity:** - **Genetic Diversity:** Variation at the level of individual genes, often related to adaptability to varying environments. - **Species Diversity:** It pertains to the number and richness of the species in a region. - **Ecosystem Diversity:** The variations in the ecosystems found in a region or the variation in ecosystems over the whole planet. 3. **Systematics:** - It involves classification and also relationships among organisms through time and space. - The process of classification involves three steps – characterization, identification, and naming. 4. **Taxonomy:** - Taxonomy is a branch of biology that deals with identifying, naming, and classifying organisms. - It involves various activities like description, identification, nomenclature, and classification of organisms. 5. **Classification:** - Classification is the process of placing living things into groups, based on certain similarities. - The primary goal is to help in easy identification and to predict the characteristics of its members. 6. **Binomial Nomenclature:** - Proposed by Carl Linnaeus, it involves naming an organism using two names – the generic name and the specific name. - The names are generally derived from Latin and are written in italics or underlined separately. 7. **Herbaria and Museums:** - Places where plant specimens (in herbaria) and animal specimens (in museums) are kept in an orderly manner, which can be used for future studies. 8. **Botanical Gardens and Zoological Parks:** - These are places where living plants and animals are kept for ex-situ conservation and research purposes. 9. **Taxonomic Aids:** - These refer to the tools which help in the identification, naming, and classification of species. - Examples include herbarium, botanical gardens, monographs, catalogues, etc. 10. **Hierarchical Levels of Classification:** - Classification involves hierarchy, which includes successive levels or categories, such as Kingdom, Division/Phylum, Class, Order, Family, Genus, and Species. ### Possible Exam Questions: 1. Describe the hierarchy of classification established by taxonomists. 2. Explain the importance of biodiversity and its levels. 3. How does binomial nomenclature work? Provide examples. 4. Describe various taxonomic aids and their importance. 5. Discuss the significance of herbaria and botanical gardens in taxonomy. ### Additional Notes: - **Importance of Classification:** - Facilitates the identification of organisms. - Helps to establish the relationship among various groups of organisms. - Provides information regarding the evolution of organisms. - **Monograph:** It contains information about any one taxon. - **Flora:** It contains actual account of habitat and distribution of plants of a given area. #### Important Terms: - **Taxon:** A taxonomic group of any rank, such as a species, family, or class. - **Phylum:** The primary subdivision of a taxonomic kingdom, grouping together all classes of organisms that have the same body plan. Remember to focus on the critical aspects, like binomial nomenclature, taxonomic hierarchy, and tools used in taxonomy, as they are fundamental to understanding the concept of the living world and its diversity.

Exam Notes: Class 11 Biology – Chapter 1: The Living World Topic: Taxonomy and Systematics
### Exam Notes: Class 11 Biology - Chapter 1: The Living World **Topic: Taxonomy and Systematics** #### Key Points: 1. **Taxonomy:** - **Definition:** Taxonomy is the science of naming, defining, and classifying groups of biological organisms based on shared characteristics. - **Elements:** Description, Identification, Nomenclature, and Classification. - **Binomial Nomenclature:** A universal system of naming that uses two Latin names: Genus and species, proposed by Carl Linnaeus. The names are italicized (or underlined when handwritten). 2. **Systematics:** - **Definition:** Systematics aims to organize biodiversity in a way that reflects the evolutionary relationships among a set of organisms or among different groups. - **Role:** It helps in revealing the phylogenies of the species under study and categorizing organisms based on their evolutionary history and resemblance. 3. **Hierarchy of Taxonomical Classification:** - There are several hierarchical taxonomic ranks: Kingdom > Division (for plants) or Phylum (for animals) > Class > Order > Family > Genus > Species. 4. **Taxonomical Aids:** - **Herbarium:** A collection of preserved plants stored, catalogued, and arranged systematically for study by botanists. - **Botanical Gardens:** These gardens maintain and display a wide range of plants, labelled with their botanical names, family, and other details. - **Museums:** Institutions where collections of preserved plants and animals, fossils, skeletons, etc., are kept for study and public viewing. - **Zoological Parks:** Places where wild animals are kept within enclosures, displayed to the public, and in which they may also breed. - **Key:** A key is a taxonomic aid used to identify plants and animals based on similarities and differences. ### Possible Exam Questions: 1. Distinguish between taxonomy and systematics in biology. 2. Explain the binomial system of nomenclature with appropriate examples. 3. What is a taxonomic hierarchy? Describe the different ranks in the hierarchy. 4. Enumerate and describe the various taxonomical aids with their purposes. 5. Why are biological names binomial and always written in a particular fashion? ### Additional Notes: - **Species:** The basic unit in taxonomy and is always written in italics (or underlined) and the first letter of the genus name is capitalized, while that of the species name is in lowercase. - **Importance of Taxonomy:** Helps in identifying and classifying living organisms into groups for easier study, understanding, and reference. - **Biological Classification:** Grouping of organisms into logically acceptable categories. - **Nomenclature:** It deals with the assignment of names to taxonomic groups in agreement with published rules. - **Flora, Manuals, and Monographs:** These are also important taxonomical aids, providing comprehensive data about the habitat and distribution of plants within a particular area. #### Important Terms: - **Phenetic Classification:** The classification of organisms based on the overall similarity, generally in appearance, between individuals. - **Cladistics:** A type of biological classification that groups organisms based on the most recent common ancestor and descendant branching. Always ensure to familiarize yourself with terminologies and their definitions, classification examples, and the importance of each aspect in taxonomy and systematics for a comprehensive understanding. Remember, practical examples and clear definitions strengthen theoretical knowledge.

Exam Notes: Class 11 Biology – Chapter 1: The Living World Topic: Species concept
### Exam Notes: Class 11 Biology - Chapter 1: The Living World **Topic: Species Concept** #### Key Points: 1. **Definition of Species:** - A species is a group of individuals that are capable of interbreeding and producing fertile offspring in a natural setting. - It is the basic unit of classification in taxonomy. 2. **Characteristics of Species:** - **Morphological Similarity:** Members have similar physical characteristics and structure. - **Reproductive Isolation:** Can breed among themselves and produce fertile offspring but are isolated from other species. - **Genetic Make-up:** Share a common gene pool. - **Ecological Niche:** Occupy the same ecological niche in nature. 3. **Types of Species Concept:** - **Biological Species Concept:** Defines species based on interbreeding and reproductive isolation from other groups. - **Morphological Species Concept:** Classifies species based on morphological (structural) similarities. - **Ecological Species Concept:** Classifies species based on their ecological niches and roles in an ecosystem. - **Phylogenetic Species Concept:** Defines species based on the phylogenetic history and common ancestry. 4. **Biodiversity:** - Refers to the variety of organisms existing on Earth, their interrelationships, and their ecosystems. - Holds significance for ecosystem stability, sustainability, and maintaining ecological balance. 5. **Importance of Defining and Identifying Species:** - Crucial for studying and conserving biodiversity. - Essential for understanding the functioning, structure, and history of ecosystems. 6. **Challenges in Defining Species:** - **Hybridization:** Some species can interbreed and produce hybrids. - **Polymorphism:** Different forms or morphs within the same species. - **Cryptic Species:** Species that look identical but are genetically different. ### Possible Exam Questions: 1. Define the term ‘species’ and describe its characteristics. 2. Explain various types of species concepts and highlight their differences. 3. Discuss the significance of identifying and categorizing organisms into specific species. 4. Explain the challenges faced by scientists in defining and identifying species. 5. Describe the importance of biodiversity in relation to the species concept. ### Additional Notes: - **Nomenclature:** The binomial system of nomenclature involves assigning two names to an organism – generic name and specific epithet. - **Role of Taxonomy:** Taxonomy plays a vital role in the classification and naming of species based on detailed studies and predefined principles. - **Subspecies:** When populations within a species become significantly different morphologically and geographically, they are considered subspecies. - **Hybrids:** Result from the mating of two different species, usually sterile, limiting gene flow between the species. #### Important Terms: - **Allopatric Speciation:** The formation of new species due to geographical isolation. - **Sympatric Speciation:** The evolution of new species within the same geographical area. Ensure that you understand each species concept thoroughly with examples and are able to articulate the challenges in defining species. Understanding the importance of species classification in biodiversity and ecosystem studies is also pivotal.

Exam Notes: Class 11 Biology – Chapter 2: Biological classification – Kingdom Monera and Protista
### Exam Notes: Class 11 Biology - Chapter 2: Biological Classification #### Topic: Kingdom Monera and Protista #### Kingdom Monera 1. **Definition and Characteristics** - **Unicellular Organisms:** Monerans are unicellular prokaryotes. - **Nucleus:** Lack a defined nucleus and membrane-bound organelles. - **Cell Wall:** Typically possess a rigid cell wall. 2. **Classification** - **Bacteria** - **Shape:** Cocci (spherical), Bacilli (rod-shaped), Spirilla (spiral). - **Reproduction:** Mostly asexual (binary fission), some exchange genetic material through conjugation. - **Cyanobacteria** (Blue-Green Algae) - **Pigments:** Possess chlorophyll-a and perform oxygenic photosynthesis. - **Nitrogen Fixation:** Some are nitrogen fixers (e.g., Nostoc). 3. **Economic Importance** - **Positive Role:** In fermentation, nitrogen fixation, and as decomposers. - **Negative Role:** Cause diseases like tuberculosis, cholera. 4. **Archaebacteria** - **Habitat:** Extreme habitats like hot springs, salty areas (halophiles), marshy areas (methanogens). #### Kingdom Protista 1. **Definition and Characteristics** - **Single-Celled Eukaryotes:** Protists have a well-defined nucleus and membrane-bound organelles. - **Diverse Group:** Include plant-like, animal-like, and fungus-like protists. 2. **Classification** - **Chrysophytes:** Include diatoms and golden algae. - **Diatoms:** Have a silica-rich cell wall and are important for oxygen production. - **Golden Algae:** Unicellular, biflagellate, found in fresh and marine waters. - **Dinoflagellates:** Mostly marine and photosynthetic. - **Cell Wall:** Made up of cellulose plates. - **Bioluminescence:** Some exhibit bioluminescence. - **Euglenoids:** Freshwater organisms with two flagella and no cell wall. - **Slime Moulds:** Resemble fungi due to spore formation. - **Types:** Plasmodial (multinucleate) and cellular (single-nucleus) slime moulds. - **Protozoans:** Animal-like protists. - **Amoeboid:** Unicellular, shape-changing organisms, e.g., Amoeba. - **Flagellates:** Have one or more flagella, e.g., Trypanosoma. - **Ciliates:** Use cilia for movement, e.g., Paramecium. - **Sporozoans:** Include non-motile parasites, e.g., Plasmodium. 3. **Reproduction** - Typically asexual through binary fission or multiple fission. - Sexual reproduction observed in some, like ciliates. 4. **Economic Importance** - **Positive Role:** Diatoms in the formation of diatomaceous earth. - **Negative Role:** Plasmodium causing malaria, Trypanosoma causing sleeping sickness. #### Possible Exam Questions: - Compare and contrast the characteristics of Kingdom Monera and Protista. - Discuss the significance and applications of cyanobacteria and diatoms. - Describe different protozoans based on their mode of locomotion and give examples. - Explain the bioluminescence property of dinoflagellates and its significance. - Discuss the economic importance of Monera and Protista. #### Additional Notes: - Protista bridges the gap between the simple organisms of Monera and the complex organisms of the subsequent kingdoms. - The existence of archaebacteria in extreme habitats is an exciting area of study for extremophiles and astrobiology. Remember to delve into the characteristics, classification, and applications of each group within the kingdoms for a comprehensive understanding and ability to tackle exam questions effectively.

Exam Notes: Class 11 Biology – Chapter 2: Biological classification – Kingdom Fungi
### Exam Notes: Class 11 Biology - Chapter 2: Biological Classification #### Topic: Kingdom Fungi **Overview:** Fungi are eukaryotic, non-vascular organisms that have a rigid cell wall and are found in terrestrial ecosystems. They show a great diversity in morphology and habitat. #### 1. Characteristics of Fungi: - **Cell Wall Composition:** Made of chitin. - **Nutrition Mode:** Heterotrophic, majorly saprophytic, parasitic, and mutualistic. - **Reproduction:** Can be asexual (spore formation) and sexual (involving complex life cycles). #### 2. Classification of Fungi: - **Zygomycetes:** - *Example:* Rhizopus. - *Reproduction:* Asexual through sporangia and sexual through zygospore formation. - **Ascomycetes:** - *Example:* Saccharomyces (yeast), Aspergillus. - *Features:* Known as sac fungi due to the sac-like structure (ascus) where spores are produced. - **Basidiomycetes:** - *Example:* Agaricus (mushroom), Ustilago (smut fungi). - *Features:* Characterized by the formation of a structure known as a basidium. - **Deuteromycetes:** - *Example:* Alternaria, Colletotrichum. - *Features:* Also known as fungi imperfecti as they do not have a sexual phase in their life cycle. #### 3. Mycorrhizae: - **Definition:** Symbiotic association between fungi and plant roots. - **Types:** Ectomycorrhizae (external) and Endomycorrhizae (internal). - **Significance:** Enhances nutrient absorption in plants. #### 4. Lichens: - **Composition:** Symbiotic association between algae (or cyanobacteria) and fungi. - **Types:** - *Crustose* (adherent to the substrate), - *Foliose* (leaf-like), - *Fruticose* (shrub-like). - **Ecological Significance:** Pioneer species in ecological succession. #### 5. Economic Importance: - **Positive:** - *Food Source:* Certain fungi like mushrooms are edible. - *Medicinal Value:* Penicillium is used to produce antibiotics. - *Biotechnological Applications:* Yeast (Saccharomyces) in brewing and baking. - **Negative:** - *Pathogenicity:* Some fungi cause diseases in plants, animals, and humans, e.g., Rust and Smut fungi in plants, Ringworm in humans. #### Possible Exam Questions: - Elaborate on the economic importance of fungi with suitable examples. - Explain the role of fungi in ecological systems, particularly in symbiotic relationships like mycorrhizae and lichens. - Detail the characteristics and examples of different classes of fungi. - Discuss the reproductive mechanisms observed in fungi. #### Additional Tips: - Diving deep into the unique features of each fungal class and understanding the complexity of their reproductive cycles can be helpful for the exam. - Relate the theoretical knowledge with practical applications or instances, such as the use of fungi in industrial processes or medical uses. Ensure to review illustrations and diagrams of different fungi, as visual elements can significantly aid in remembering their characteristics and differentiating between them.

Exam Notes: Class 11 Biology – Chapter 2: Biological classification – Kingdom Plantae and Animalia
### Exam Notes: Class 11 Biology - Chapter 2: Biological Classification #### Topic: Kingdom Plantae and Animalia --- ### Kingdom Plantae #### Characteristics - **Autotrophic**: Capable of synthesizing their own food. - **Cell Wall**: Presence of cell wall composed of cellulose. - **Reproduction**: Engage in both sexual and asexual reproduction. #### Classification - **Thallophyta**: Lack well-differentiated body structures (e.g., algae). - **Bryophyta**: Known as amphibians of the plant kingdom due to their dependence on water for reproduction (e.g., mosses). - **Pteridophyta**: Vascular plants that reproduce via spores (e.g., ferns). - **Gymnosperms**: Bear naked seeds, usually on cones (e.g., pines). - **Angiosperms**: Flowering plants that produce seeds enclosed in fruit. #### Economic Importance - Source of oxygen, food, medicine, timber, and more. #### Points of Focus - Difference in reproduction methods across groups. - Adaptation to habitats and ecological roles. ### Kingdom Animalia #### Characteristics - **Heterotrophic**: Cannot synthesize their own food. - **Multicellular**: Composed of multiple cells with a high level of complexity. - **Locomotion**: Capable of movement. #### Classification - **Porifera**: Simplest animals, non-mobile (sponges). - **Coelenterata (Cnidaria)**: Aquatic, mostly marine animals with tentacles (jellyfish, sea anemones). - **Platyhelminthes**: Flatworms, can be parasitic (tapeworms, liver flukes). - **Nematoda**: Roundworms, many of which are parasitic (hookworms). - **Annelida**: Segmented worms (earthworms, leeches). - **Arthropoda**: Largest phylum, exoskeleton, jointed appendages (insects, spiders, crustaceans). - **Mollusca**: Soft-bodied, generally covered by a hard shell (snails, oysters). - **Echinodermata**: Marine animals, radial symmetry (starfish, sea urchins). - **Chordata**: Possess a notochord during some stage of their development (fish, mammals). #### Economic and Ecological Importance - Source of food, aiding in pollination, disease vectors, etc. #### Points of Focus - Distinguish between various phyla based on their characteristics. - Understand the diversity and adaptation mechanisms within the kingdom. ### Potential Exam Questions - Explain the economic and ecological significance of Kingdom Plantae. - Differentiate between various classes within Kingdom Plantae and Kingdom Animalia. - Describe adaptive features of animals that allow them to survive in various habitats. - Explain the role of Kingdom Animalia in maintaining ecological balance. ### Additional Tips - Pay attention to unique characteristics that differentiate one group/class/phylum from another. - Explore the evolutionary relationships and complexity gradient across different groups. - Relate theoretical aspects to real-world instances for better memory retention. Understanding the diversity, characteristics, and ecological roles of organisms in Kingdom Plantae and Animalia will form a foundational knowledge for exploring more advanced biological concepts in subsequent chapters.

Exam Notes: Class 11 Biology – Chapter 2: Biological classification – Viruses, Viroids, and Lichens
### Exam Notes: Class 11 Biology - Chapter 2: Biological Classification #### Topic: Viruses, Viroids, and Lichens --- ### Viruses #### Characteristics - **Acellular Entities**: Not considered living organisms; require a host cell to replicate. - **Genetic Material**: Contain DNA or RNA, but not both, enclosed within a protein coat (capsid). - **Reproduction**: Only within a host cell using the host’s machinery. #### Disease Causing - Example: HIV, Influenza, Corona Virus, etc. #### Points of Focus - Understanding of the viral replication cycle. - The distinct nature of viruses as compared to other life forms. ### Viroids #### Characteristics - **Smallest Infectious Agents**: Consist only of RNA, no protein coat. - **Disease-Causing**: Primarily cause diseases in plants. #### Points of Focus - Mechanism through which viroids cause disease in plants. - Differences between viroids and viruses. ### Lichens #### Characteristics - **Symbiotic Association**: Between algae (or cyanobacteria) and fungi. - **Algae**: Provides food via photosynthesis. - **Fungi**: Provides protection and absorbs nutrients. #### Ecological Importance - **Pioneer Species**: First to colonize barren or disturbed areas. - **Bioindicators**: Indicate air pollution levels. #### Types - **Crustose**: Adhering closely to the substrate. - **Foliose**: Leaf-like structure. - **Fruticose**: Shrubby or bushy structure. #### Points of Focus - Understanding symbiotic relationships. - The ecological role of lichens in environment and ecosystem. ### Potential Exam Questions - Explain the disease mechanism of viruses and give examples of virus-caused diseases. - What is the biological significance of the symbiotic relationship found in lichens? - Differentiate between the structures of viruses and viroids and explain how they reproduce. - Discuss the role of lichens in ecological succession and as bioindicators. ### Additional Tips - Ensure to understand how the entities in this topic deviate from typical biological classification. - Relate the theoretical aspects of viruses and viroids to real-world diseases and occurrences. - Consider drawing diagrams of viruses and lichen types to enhance visual memory. Understanding these non-classical entities (viruses and viroids) and symbiotic relationships (lichens) will broaden your perspective on biological classification and deepen your insight into the variety and complexity of life. Make sure to tie these notes to the broader curriculum and revise them thoroughly as you prepare for your exam!

Exam Notes: Class 11 Biology – Chapter 3: Plant Kingdom
### Exam Notes: Class 11 Biology - Chapter 3: Plant Kingdom --- ### Introduction - **Study of Plant Kingdom**: Involves understanding the classification of plant organisms based on distinct features. ### Classification of Plant Kingdom The Plant Kingdom is majorly divided into five divisions: 1. **Algae** - Characteristics: Simple, autotrophic, largely aquatic. - Examples: Spirogyra, Chlorella. - Points of Focus: Thallus organization, types of reproduction. 2. **Bryophytes** - Characteristics: Terrestrial, non-vascular plants, known as "amphibians of the plant kingdom". - Examples: Marchantia (Liverwort), Funaria (Moss). - Points of Focus: Plant body differentiation, role in succession on barren lands. 3. **Pteridophytes** - Characteristics: Possess vascular tissues but no seeds. - Examples: Pteris (Fern), Equisetum (Horsetail). - Points of Focus: First terrestrial plants, reproduction mechanism. 4. **Gymnosperms** - Characteristics: Vascular plants with naked seeds. - Examples: Pinus, Cycas. - Points of Focus: Adaptations to land, type of seeds, and leaves. 5. **Angiosperms** - Characteristics: Vascular plants with flowers and seeds inside fruits. - Examples: Mango, Wheat. - Points of Focus: Types (monocots and dicots), flower structure, pollination. ### Important Concepts - **Alternation of Generations**: Occurrence of haploid (gametophytic) and diploid (sporophytic) generations alternatively. - **Evolutionary Trends**: Progression from simple to complex organisms. - **Adaptation**: How different plants have adapted to their environments. ### Potential Exam Questions - Describe the alternation of generations in bryophytes. - Compare and contrast the reproductive strategies of gymnosperms and angiosperms. - Explain the evolutionary significance of seed production in plants. - Describe the life cycle of a named algae and a pteridophyte. ### Additional Tips - Create comparative tables to understand differences and similarities among the divisions. - Practice drawing life cycles of representatives from each division. - Understand the historical significance and evolutionary progression among plant divisions. ### Conclusion Understanding the classification and life cycles of plants within the Plant Kingdom is crucial. Ensure to review the characteristics and examples of each group, focusing on their reproductive strategies and adaptational features. Additionally, understand the evolutionary context and ecological significance of each division in the Plant Kingdom to enhance your exam preparation.

Exam Notes: Class 11 Biology – Chapter 4: Animal Kingdom
### Exam Notes: Class 11 Biology - Chapter 4: Animal Kingdom --- ### Introduction The **Animal Kingdom** is characterized by multicellular, eukaryotic organisms that are heterotrophic in nature. Classification within the Animal Kingdom is largely based on certain fundamental characteristics like modes of nutrition, symmetry, body organization, and reproductive methods. ### Major Classifications in the Animal Kingdom: 1. **Porifera** - Characteristics: Sessile, canal system, spicules. - Example: Sponges. - Note: First multicellular animals, asymmetrical. 2. **Coelenterata (Cnidaria)** - Characteristics: Radial symmetry, tentacles, cnidocytes. - Example: Hydra, Jellyfish. - Note: First animals with a true body cavity. 3. **Platyhelminthes** - Characteristics: Bilateral symmetry, acoelomates, flat bodies. - Example: Tape worm, Liver fluke. 4. **Nematoda** - Characteristics: Bilateral symmetry, pseudocoelom, cylindrical bodies. - Example: Ascaris. 5. **Annelida** - Characteristics: Bilateral symmetry, true coelom, segmented body. - Example: Earthworm. 6. **Arthropoda** - Characteristics: Exoskeleton, jointed appendages. - Example: Spider, Crab, Ant. - Note: Largest phylum of Animal Kingdom. 7. **Mollusca** - Characteristics: Soft-bodied, muscular foot, mantle. - Example: Snail, Octopus. 8. **Echinodermata** - Characteristics: Radial symmetry, spiny skin. - Example: Starfish. 9. **Chordata** - Characteristics: Notochord, dorsal hollow neural cord. - Note: Includes Vertebrates. ### Important Concepts: - **Levels of Organization**: Cellular level to organ-system level. - **Body Symmetry**: Asymmetry, radial symmetry, bilateral symmetry. - **Coelom Development**: Acoelomates, pseudocoelomates, and coelomates. - **Notochord Presence**: Invertebrates and vertebrates. ### Potential Exam Questions: - Differentiate between acoelomates, pseudocoelomates, and coelomates with examples. - Describe the characteristics that distinguish arthropods from annelids. - Discuss the significance of bilateral symmetry in the evolutionary context. - Explain the key features of echinoderms and their adaptation to a marine environment. ### Additional Tips: - Diagrams: Familiarize yourself with the basic anatomy of examples from each phylum. - Comparative Tables: Utilize tables to draw comparisons between different phyla regarding symmetry, body organization, and coelom. - Evolutionary Aspects: Understand the evolutionary significance of certain characteristics like body symmetry, coelom, and notochord. ### Conclusion: Understanding the Animal Kingdom involves recognizing the critical features and examples of each phylum and comprehending the evolutionary significance of each classification. Ensure thorough understanding and revision of each phylum's characteristics, representative organisms, and distinctive features. This detailed insight will help create a holistic understanding of the chapter and enhance your preparation for exams.

Exam Notes: Class 11 Biology – Chapter 5: Morphology of Flowering Plants
### Exam Notes: Class 11 Biology - Chapter 5: Morphology of Flowering Plants --- ### Introduction "Morphology of Flowering Plants" explores the different parts of a flowering plant and the diverse forms and functions they have. Understanding the various structural parts helps in studying plant diversity and also, plays a pivotal role in the classification and identification of plants. ### Key Concepts 1. **Root** - Function: Absorption, anchorage, and storage. - Types: Tap root, fibrous root, and adventitious root. - Modifications: For storage (e.g., carrot), for support (e.g., prop roots of banyan), etc. 2. **Stem** - Function: Support, transportation, and storage. - Types: Herbaceous and woody. - Modifications: For storage (e.g., potato), for protection (e.g., thorns of citrus), etc. 3. **Leaf** - Function: Photosynthesis, transpiration, and gaseous exchange. - Parts: Leaf base, petiole, and lamina. - Modifications: For storage (e.g., onion), for catching prey (e.g., pitcher plant), etc. 4. **Flower** - Function: Reproduction. - Parts: Sepal, petal, stamen, and carpel. - Types: Unisexual and bisexual. 5. **Fruit** - Function: Protects seeds and aids in their dispersal. - Types: Simple, aggregate, and composite. 6. **Seed** - Function: Reproduction and dispersal. - Parts: Seed coat, embryo, and endosperm. ### Inflorescence - **Racemose**: The main axis continues to grow, and flowers are borne in an acropetal succession. - **Cymose**: Limited growth of the main axis and flowers are borne in a basipetal succession. ### Plant Life Cycle - Alternation between haploid gametophyte and diploid sporophyte. ### Flower Structure - Arrangement and numbers of floral parts play a crucial role in the classification of angiosperms. - **Androecium**: All stamens in a flower. - **Gynoecium**: All carpels in a flower. ### Potential Exam Questions: - Explain the different types of root modifications with examples. - Describe the structure of a typical angiospermic flower with a labeled diagram. - Differentiate between racemose and cymose inflorescence. - Write short notes on the modifications of leaves. ### Additional Tips: - **Diagrams**: Practice drawing and labeling diagrams of different plant parts. - **Modifications**: Focus on the various modifications of plant parts and their functions. - **Terminologies**: Ensure clarity on terminologies like venation, phyllotaxy, placentation, etc. - **Inflorescence**: Understand the different types and be able to differentiate between them. ### Conclusion: Plant morphology provides a foundation for understanding the vast diversity seen in the plant kingdom. The structure and modifications of each plant part are crucial to not only understand their function but also to identify and classify plants in systematic botany. Ensure to revisit and revise these notes to have a thorough understanding and to perform well in your exams.

Exam Notes: Class 11 Biology – Chapter 5: Anatomy of Flowering Plants
### Exam Notes: Class 11 Biology - Chapter 5: Anatomy of Flowering Plants --- ### Introduction Anatomy in plants deals with the study of the internal structure of organisms. In flowering plants, anatomy helps in understanding the structural adaptation to their environment and lifestyle. ### Key Concepts 1. **Tissues in Plants** - **Meristematic Tissues**: Actively dividing cells, responsible for plant growth. - Apical Meristem: Located at root and shoot tips. - Lateral Meristem: Leads to an increase in girth/diameter. - **Permanent Tissues**: Cells that have lost the ability to divide. - Simple Tissues: Made of similar types of cells (e.g., parenchyma). - Complex Tissues: Comprising different types of cells (e.g., xylem). 2. **Anatomy of Root** - **Epiblema**: The outermost layer, which is in direct contact with the soil. - **Cortex**: Lies below the epidermis, mainly made up of parenchyma. - **Endodermis**: The innermost layer of the cortex. - **Pericycle**: Thin layer of cells found just inside the endodermis. - **Vascular Bundle**: Consists of xylem and phloem tissues. 3. **Anatomy of Stem** - **Epidermis**: Outermost protective layer, often covered with a cuticle. - **Cortex**: Lies beneath the epidermis, consists of parenchyma, collenchyma, and sclerenchyma. - **Vascular Bundles**: Arranged in a ring, with xylem on the inside and phloem on the outside. - **Pith**: Central part, composed mainly of parenchyma. 4. **Anatomy of Leaf** - **Epidermis**: Upper and lower epidermis covered with a waxy cuticle. - **Mesophyll**: Found between the upper and lower epidermis; differentiated into palisade and spongy parenchyma. - **Vascular Bundles**: Comprising xylem and phloem, often surrounded by a bundle sheath. 5. **Secondary Growth** - Formation of secondary tissues from the lateral meristems. - Results in an increase in the girth of the stem and root. - The formation of annual rings helps determine the age of the plant. ### Potential Exam Questions - Describe the anatomy of dicot roots with labeled diagrams. - Differentiate between meristematic and permanent tissues. - Explain the secondary growth in dicot stems. - Write short notes on the anatomical features of leaves. ### Additional Tips - **Diagrams**: Ensure that you can draw and label the transverse section of roots, stems, and leaves. - **Tissue Types**: Be clear on the different plant tissue types and their functions. - **Anatomical Differences**: Be able to differentiate between dicot and monocot structures. - **Secondary Growth**: Understand the process and significance of secondary growth in plants. ### Conclusion Understanding the anatomy of flowering plants is pivotal in understanding their functions and life processes better. Examining how plants adapt their internal structures to accommodate various functions and environmental factors is also crucial. Ensure to regularly revisit these concepts, and practice diagrams to solidify your understanding for the exams.

Exam Notes: Class 11 Biology – Chapter 7: Structural Organisation in Animals – Animal tissues
### Exam Notes: Class 11 Biology - Chapter 7: Structural Organisation in Animals - Animal Tissues ## Introduction Animal tissues are specialized groups of cells that work together to perform a specific function. They vary with respect to their structure, function, and locations. ## Types of Animal Tissues Animal tissues are broadly categorized into four types: ### 1. **Epithelial Tissue** - **Functions**: Protection, secretion, absorption, and sensation - **Types**: - **Simple Epithelium**: Single-layered (e.g., simple squamous, simple cuboidal, and simple columnar) - **Stratified Epithelium**: Multi-layered (e.g., stratified squamous) - **Glandular Epithelium**: Involved in secretion (e.g., goblet cells) ### 2. **Connective Tissue** - **Functions**: Binds, supports, and protects tissues and organs of the body. - **Types**: - **Loose Connective Tissue**: Provides support (e.g., areolar tissue) - **Dense Connective Tissue**: Offers strength and flexibility (e.g., tendons) - **Specialized Connective Tissues**: E.g., bone, blood, and cartilage ### 3. **Muscular Tissue** - **Functions**: Produces force and motion. - **Types**: - **Skeletal Muscle**: Voluntary, striated muscle attached to bones - **Smooth Muscle**: Involuntary, non-striated muscle found in organs - **Cardiac Muscle**: Involuntary, striated muscle found in the heart ### 4. **Nervous Tissue** - **Functions**: Receives stimuli and transmits electrical impulses. - **Main Components**: - **Neurons**: Basic units that transmit nerve impulses - **Neuroglia**: Cells that provide support to neurons ## Detailed Note on Each Tissue Type ### Epithelial Tissue - **Location**: Lines the body cavities, organs, and surfaces. - **Characteristics**: Cells are closely packed with little intercellular material. - **Functions**: Involves protection from mechanical injury, pathogens, and desiccation. ### Connective Tissue - **Location**: Throughout the body, offering structural and metabolic support. - **Characteristics**: Sparsely packed cells scattered through an extracellular matrix. - **Functions**: Providing physical support, transporting substances, and storing energy reserves. ### Muscular Tissue - **Location**: Attached to bones, in the walls of hollow organs, and heart. - **Characteristics**: Contains cells with contractile filaments for movement. - **Functions**: Movement, maintaining posture, and producing heat. ### Nervous Tissue - **Location**: Brain, spinal cord, and peripheral nerves. - **Characteristics**: Consists of neurons and supporting cells. - **Functions**: Transmitting electrical signals and processing information. ## Conclusion Understanding the various types of tissues and their respective roles provides an insight into the complex structural organization in animals. This foundational knowledge is crucial for delving into more complex physiological processes and systems in animals. ### Quick Review - **Epithelial Tissue**: Protects and defines boundaries. - **Connective Tissue**: Supports and binds tissues together. - **Muscular Tissue**: Enables movement through contraction. - **Nervous Tissue**: Conveys and processes electrical signals. Ensure you understand the role and significance of each tissue type, examples, and where they are found in the body, as these are commonly explored aspects in exams.

Exam Notes: Class 11 Biology – Chapter 7: Structural Organisation in Animals – Morphology and anatomy of an earthworm, cockroach, and frog
### Exam Notes: Class 11 Biology - Chapter 7: Structural Organisation in Animals - Morphology and Anatomy of an Earthworm, Cockroach, and Frog ## 1. Earthworm (Pheretima posthuma) ### Morphology - **Body Shape**: Long, cylindrical, segmented (metamerism) - **Color**: Dorsal surface - dark brown; ventral surface - lighter - **Sensory Organs**: Poorly developed. Sensory organs related to touch and light intensity ### Anatomy - **Body Segments**: Have numerous segments, each having setae - **Digestive System**: Alimentary canal is a straight tube, mouth -> anus - **Circulatory System**: Closed type; heart consists of several paired aortic arches - **Reproductive System**: Hermaphrodite, contain both male and female reproductive organs ## 2. Cockroach (Periplaneta americana) ### Morphology - **Body Division**: Divided into head, thorax, and abdomen - **Color**: Brown-bodied with a hard exoskeleton - **Appendages**: Three pairs of legs, two pairs of wings (in males) ### Anatomy - **Digestive System**: Divided into foregut, midgut, and hindgut - **Respiratory System**: Network of tracheae, controlled by spiracles - **Circulatory System**: Open type; blood vessels open into body cavity (hemocoel) - **Reproductive System**: Sexes are separate; males have testes and females have ovaries ## 3. Frog (Rana tigrina) ### Morphology - **Body Shape**: Sturdy, streamlined, bifurcated into head+trunk and hind limbs - **Skin**: Smooth and slimy, contains chromatophores which help in camouflage - **Sensory Organs**: Eyes have eyelids and a nictitating membrane; tympanum represents the ear ### Anatomy - **Digestive System**: J-shaped alimentary canal and associated digestive glands - **Circulatory System**: Closed type with a three-chambered heart (2 atria, 1 ventricle) - **Respiratory System**: Pulmonary respiration through lungs; cutaneous respiration through skin - **Reproductive System**: Separate sexes; male has vocal sacs and copulatory pad on the first digit of the hind limb ## Comparative Notes ### - Circulatory System - **Earthworm**: Closed type - **Cockroach**: Open type - **Frog**: Closed type ### - Reproductive System - **Earthworm**: Hermaphrodite - **Cockroach**: Unisexual - **Frog**: Unisexual ### - Respiratory System - **Earthworm**: Through skin - **Cockroach**: Tracheal system - **Frog**: Lungs and skin ## Conclusion Understanding the structural organization of various animals like earthworms, cockroaches, and frogs entails focusing on the key morphological and anatomical features that distinguish them. This comprehensive review of the diverse organisms provides a baseline to comprehend the complexity and variability in the animal kingdom. ### Quick Review - **Earthworm**: Segmented, hermaphroditic, respires through skin - **Cockroach**: Hard exoskeleton, unisexual, tracheal respiration - **Frog**: Slimy skin, unisexual with external fertilization, pulmonary and cutaneous respiration Remember to explore each feature in-depth, as this comparative understanding builds the foundation for understanding advanced concepts in animal biology.

Exam Notes: Class 11 Biology – Chapter 7: Structural Organisation in Animals – Morphology and anatomy of an earthworm, cockroach, and frog
### Exam Notes: Class 11 Biology - Chapter 7: Structural Organisation in Animals - Morphology and Anatomy of an Earthworm, Cockroach, and Frog ## 1. Earthworm (Pheretima posthuma) ### Morphology - **Body Shape**: Long, cylindrical, segmented (metamerism) - **Color**: Dorsal surface - dark brown; ventral surface - lighter - **Sensory Organs**: Poorly developed. Sensory organs related to touch and light intensity ### Anatomy - **Body Segments**: Have numerous segments, each having setae - **Digestive System**: Alimentary canal is a straight tube, mouth -> anus - **Circulatory System**: Closed type; heart consists of several paired aortic arches - **Reproductive System**: Hermaphrodite, contain both male and female reproductive organs ## 2. Cockroach (Periplaneta americana) ### Morphology - **Body Division**: Divided into head, thorax, and abdomen - **Color**: Brown-bodied with a hard exoskeleton - **Appendages**: Three pairs of legs, two pairs of wings (in males) ### Anatomy - **Digestive System**: Divided into foregut, midgut, and hindgut - **Respiratory System**: Network of tracheae, controlled by spiracles - **Circulatory System**: Open type; blood vessels open into body cavity (hemocoel) - **Reproductive System**: Sexes are separate; males have testes and females have ovaries ## 3. Frog (Rana tigrina) ### Morphology - **Body Shape**: Sturdy, streamlined, bifurcated into head+trunk and hind limbs - **Skin**: Smooth and slimy, contains chromatophores which help in camouflage - **Sensory Organs**: Eyes have eyelids and a nictitating membrane; tympanum represents the ear ### Anatomy - **Digestive System**: J-shaped alimentary canal and associated digestive glands - **Circulatory System**: Closed type with a three-chambered heart (2 atria, 1 ventricle) - **Respiratory System**: Pulmonary respiration through lungs; cutaneous respiration through skin - **Reproductive System**: Separate sexes; male has vocal sacs and copulatory pad on the first digit of the hind limb ## Comparative Notes ### - Circulatory System - **Earthworm**: Closed type - **Cockroach**: Open type - **Frog**: Closed type ### - Reproductive System - **Earthworm**: Hermaphrodite - **Cockroach**: Unisexual - **Frog**: Unisexual ### - Respiratory System - **Earthworm**: Through skin - **Cockroach**: Tracheal system - **Frog**: Lungs and skin ## Conclusion Understanding the structural organization of various animals like earthworms, cockroaches, and frogs entails focusing on the key morphological and anatomical features that distinguish them. This comprehensive review of the diverse organisms provides a baseline to comprehend the complexity and variability in the animal kingdom. ### Quick Review - **Earthworm**: Segmented, hermaphroditic, respires through skin - **Cockroach**: Hard exoskeleton, unisexual, tracheal respiration - **Frog**: Slimy skin, unisexual with external fertilization, pulmonary and cutaneous respiration Remember to explore each feature in-depth, as this comparative understanding builds the foundation for understanding advanced concepts in animal biology.

CLASS 11 CHAPTER 4: THE ANIMAL KINGDOM Notes
https://acrobat.adobe.com/id/urn:aaid:sc:EU:24b7b2f5-ad16-4f8c-93f9-bda3afb98a5c CLASS 11 CHAPTER 4: THE ANIMAL KINGDOM Levels of structural organization of a multicellular animal (1) Chemical Level. it is the lowest level of organization. Atoms join together to form molecules. (2) Cellular level. The chemicals are put together to form the cellular level. cells are the basic structural and functional units of an organism (living thing), cells are of various types, specialized for different function or functions. It is called ‘division of labour’ among the cells. (3) Tissue level. The cells that are similar in structure, origin and function form a tissue. There are four main types of tissues: epithelial, connective, muscular and nervous. (4) Organ level. it is appropriate to consider an organs as the combination of tissues into a unit for the performance of a specific function or a series functions. (5) System level. Several organs constitute an organ-system. (6) Open circulatory system: cells and tissue directly receive the blood pumping out of the heart. (7) Closed circulatory system: blood is circulated through arteries, veins and capillaries. (8) Diploblastic: embryo with two germinal layers called external ectoderm and internal endoderm, e.g. Porifera, Cnidaria. (9) Triploblastic: embryo with three germinal layers, mesoderm between ectoderm and endoderm, e.g. Platyhelminthes to Chordates. (10) Asymmetrical: no line of symmetry in the body, e.g. sponges. (11) Radial symmetry: any plane passing through centre divides the body in two symmetrical halves, e.g. coelenterates, ctenophores. (12) Bilateral symmetry: a plane divides the body in symmetrical left and right halves, e.g. annelids, arthropods, etc. (13) Body cavity between the body wall and gut wall, lined by mesoderm is called coelom • Acoelomates: body cavity is absent, e.g. Platyhelminthes • Pseudocoelomates: mesoderm is present as scattered pouches, e.g. Aschelminthes • Coelomates: having coelom (body cavity) e.g. from Annelida to Chordata (14) Earthworm’s body shows metameric segmentation. (15) Animals with notochord are called chordates, animals without notochord are called non-chordates, e.g. Porifera to Echinodermata. Characters of Non Chordata (Invertebrates) The animals which lack a notochord are called invertebrates. e.g. Amoeba, sponges, Hydra, worms, insects, etc., Invertebrates are characterized by the following salient features – (1) The vertebral column is absent. (2) the nerve cord is solid in nature. (3) The nerve cord is present on the ventral side and never on the dorsal side. (4) When alimentary canal is present, it lies dorsal to the nerve cord. (5) Invertebrates may be acoelomate or pseudocoelomate or true coelomate. (6) They have either asymmetry or radial symmetry or bilateral symmetry. (7) The circulatory system is open type or closed type. (8) They exhibit all possible type of reproduction. Characters of Chordata (Vertebrates) The animals which possess a notochord are called vertebrates. (1) Aquatic, aerial or terrestrial. (2) Body small to large, bilaterally symmetrical and metamerically segmented. (3) A post anal tail usually projects beyond the anus at some stage and may or may not persist in the adult. (4) Exoskeleton often present; well developed in most vertebrates. (5) Body wall triploblastic with 3 germinal layers : ectoderm, mesoderm and endoderm. (6) Coelomate animals having a true coelom, enterocoelic or schizocoelic in origin. (7) A skeletal rod, the notochord, present at some stage in life cycle. (8) A cartilaginous or bony, living and jointed endoskeleton present in the majority of members (vertebrates). (9) Pharyngeal gill slits present at some stage; may or may not be functional. (10) Digestive system complete with digestive glands. (11) Blood vascular system closed. (12) Excretory system comprising proto-or meso- or meta-nephric kidneys. (13) Nerve cord dorsal and tubular. Anterior end usually enlarged to form brain. (14) Sexes separate with rare exceptions. Phylum Protozoa The name “Protozoa” was coined by Goldfuss (1817). The branch of their study is called Protozoology. Salient Features (1) Protozoans are the simple and primitive organisms (2) free living or parasitic (3) All the free living forms are aquatic (4) asymmetrical or radially symmetrical or bilaterally symmetrical (5) They are unicellular (acellular) (6) They have protoplasmic grade of organization. (7) Locomotion is affected by flagella, cilia or pseudopodia. (8) Nutrition is holophytic, holozoic, saprozoic or parasitic. (9) Digestion is intracellular (10) Excretion & Respiration occurs by diffusion (11) In fresh water protozoans osmoregulation is carried out by the contractile vacuoles. (12) Encystment is a common phenomenon (13) Reproduction occurs by asexual and sexual methods. Phylum Porifera (i) The word “Porifera” means pore bearers (Gr., porus = pore; ferre = to bear); their body wall has numerous minute pores, called ostia, through which a continuous current of outside water is drawn into the body. (ii) Phylum porifera has the following salient features: (1) All the sponges are Aquatic, Sedentary, Asymmetrical or Radially, (2) They are diploblastic. (3) The body is perforated by numerous minute pores called ost ia. (4) The ostia open into a large cavity called spongocoel. (5) The spongocoel opens to the outside by a large opening called osculum. (6) The sponges possess an endoskeleton in the form of calcareous spicules. (7) Excretion and respiration occur by diffusion. (8) They have greater power of regeneration. (9) Reproduction takes place by asexual or sexual methods. (10) Development is indirect or direct. Phylum Cnidaria (or Coelenterata) (i) ‘Tissue level’ with a radial symmetry. (ii) The term “Coelenterata” signifies the presence of a single internal cavity called coelenteron, or gastrovascular cavity, combining functions of both digestive and body cavities. The term “Cnidaria” indicates the presence of stinging cells (Gr., knide = nittle or stinging cells). (iii) Phylum coelenterata has the following salient features – ⚫ Coelenterates are multicellular organisms. ⚫ They have tissue-grade of organization. ⚫ The body is radially symmetrical. Radial symmetry is the symmetry of a wheel. ⚫ All the members of this phylum are aquatic. ⚫ They are solitary or colonial. ⚫ Polyps and medusa occur in the life cycle. ⚫ The body wall is diploblastic. ⚫ Nematocysts or stinging cells are present. ⚫ Coelom is absent; hence coelenterates are acoelomate animals. ⚫ A gastrovascular cavity or coelenteron is present. ⚫ Mouth is present; but anus is absent . ⚫ Digestion is extracellular as well as intracellular . ⚫ Respiratory, excretory and circulatory system are absent . ⚫ Nervous system is diffuse-type, formed or nerve-nets. ⚫ Reproduction is by asexual and sexual methods. ⚫ Development is indirect as there are one or two larval forms. ⚫ Life history has alternation of generations or metagenesis. Phylum Ctenophora (i) Ctenophora is a small phylum. These animals exhibit the characters of Coelenterata and platyhelminthes. (ii) Phylum Ctenophora shows the following salient features ⚫ All the ctenophores are marine. ⚫ They are solitary and pelagic. ⚫ They are transparent. ⚫ They have tissue-grade of organization. ⚫ They have biradial symmetry. ⚫ They are acoelomate animals. ⚫ They are non-segmented. ⚫ Their body-wall is diploblastic. ⚫ The mesogloea contains cells. ⚫ Nematocysts are absent. ⚫ Special adhesive cells called colloblasts are present in all ctenophores. ⚫ The gastrovascular system is well developed. ⚫ Two anal openings are present. ⚫ Skeletal system is absent. ⚫ Excretion and respiration are carried out by diffusion. ⚫ The nervous system is in the form of nerve net. ⚫ Cilia are used for locomotion. ⚫ They are hermaphrodites. ⚫ Development is indirect. It includes a larval stage. Phylum Platyhelmithes (i) “Platyhelminthes” means flatworms (Gr., platys = flat; helmins = worms); their body is dorsoventrally flattened. Salient features (1) They are dorsoventrally flattened like a leaf (2) They show organ grade of organization (3) They are acoelomate animals (4) They are triploblastic animals. (5) They are bilaterally symmetrical animals. (6) Some members have segmented body. (7) Many of the parenchyma cells give rise to muscle fibres. (8) The digestive system is completely absent from Cestoda and Acoela. (9) The respiratory organs are absent. In parasites respiration is anaerobic (10) There is no circulatory system (11) The excretory system is formed of protonephridia (flame cells) (12) The nervous system is well developed. (13) They are hermaphrodites, i.e., both male and female reproductive organs are present in the same animal (14) Fertilization is internal in them. (15) They are free-living or parasitic. Phylum – Aschelminthes Salient features: 1. Free-living or parasitic, aquatic or terrestrial. 2. Round body in cross-section, bilaterally symmetrical, triploblastic, pseudocoelomate with organ system organization. 3. The alimentary canal is complete and has a muscular pharynx. 4. Dioecious, females are longer than males. 5. Internal fertilization with direct or indirect development Examples: Ascaris (roundworm), Wuchereria (Filarial worm), Ancylostoma (hookworm) Phylum – Annelida Salient features: 1. Bilaterally symmetrical, triploblastic, coelomate, organ system organization. 2. Metamerically segmented. 3. Longitudinal and circular muscles help in locomotion. 4. Nereis, an aquatic animal has appendages called parapodia, which help in swimming. 5. Closed circulatory system. 6. Nephridia is present for osmoregulation and excretion. 7. Paired ganglia are present, which are connected to double ventral nerve cord by lateral nerves. 8. Reproduction is sexual. Nereis is dioecious, earthworm and leeches are monoecious Examples: Pheretima (earthworm), Nereis, Hirudinaria (bloodsucking leech) Phylum – Arthropoda Salient Features 1. Largest phylum with two-thirds of all known animals. 2. It contains insects. 3. Bilaterally symmetrical, triploblastic, coelomate, organ system organization. 4. Their body is covered by chitinous exoskeleton. 5. The characteristic property of the group is jointed legs. 6. Their body can be divided into three regions; head, thorax and abdomen. 7. Respiration is by trachea, gills, book gills, book lungs. 8. The circulatory system is open type. 9. Statocyst or balancing organs are present. 10. Eyes are simple or compound. 11. Malpighian tubules help in excretion. 12. Mostly dioecious, oviparous and fertilization is internal Examples: economically important species- Bombyx (silkworm), Apis (honey bee) Vector for diseases- mosquitoes like Anopheles, Aedes, Culex.Living fossil- Limulus (King crab) Phylum Mollusca (i) Basically bilaterally symmetrical, whose soft body (L., mollis or molluscum = soft) is non-segmented and enclosed within a skin– fold (mantle) which usually secretes a calcareous shell. Salient Features (1) Molluscs are multicellular organisms (2) They have a bilateral symmetry, but snails are asymmetrical (3) They are triploblastic animals. (4) They are coelomate animals. (5) They have organ system grade of organization. (6) The body is soft and non-segmented. (7) The soft body is covered by a fleshy fold of the body wall. It is called mantle. (8) The molluscs are provided with one or two calcareous shells. (9) Respiration is carried out by the gills or pulmonary chambers. (10) The digestive system is well developed. (11) The circulatory system is of an open type. (12) The excretory organ is the kidney. (13) The nervous system is well developed. (14) The sensory organs are eyes, statocysts and osphradia. (15) Sexes are separate in them, or they are hermaphrodites. (16) The development in their case in either direct or indirect Phylum Echinodermata (i) The term “Echinodermata” means spiny skin (Gr., echinos = spiny + dermatos = skin). Salient features (1) Echinoderms are exclusively marine beings. (2) They are triplobalstic and coelomate animals. (3) They have radially symmetrical body. (4) They have organ system grade of organization. (5) They have well developed (6) They have a water–vascular system with tube–feet for locomotion, feeding and respiration. (7) Circulatory system is of the open–type. (8) The sensory organs are poorly developed. (9) The excretory organs are absent. (10) They have pedicellariae. (11) Development is indirect. (12) The larval forms are bilaterally symmetrical. Phylum – Hemichordata Salient Features: 1. Presence of stomochord, a structure similar to the notochord. 2. Bilaterally symmetrical, triploblastic, coelomate, organ system organization. 3. Cylindrical body with a proboscis, a collar and a long trunk. 4. Gills are present and circulation is open type. 5. Proboscis gland works as an excretory organ. 6. Dioecious, external fertilization with indirect development. Examples: Balanoglossus, Saccoglossus Phylum Chordata • Characteristic features are a dorsal hollow nerve cord, a notochord and paired gill slits • Bilaterally symmetrical, triploblastic, coelomate, organ system organisation • The circulatory system is closed and the post-anal tail is present • Three sub-phylums come under Chordata: a. Urochordata– notochord present only in the larval tail, e.g. Ascidia, Salpa, Doliolum b. Cephalochordata– notochord present throughout life from head to tail, e.g. Branchiostoma (Lancelet or amphioxus) c. Vertebrata– Notochord is present in the embryonic stage, it gets replaced by Vertebral Column • Vertebrata is further divided into two divisions a. Agnatha (without jaws): Class Cyclostomata b. Gnathostomata (with jaws): has two Super Class: i. Pisces (bear fins): two Classes- Chondrichthyes, Osteichthyes ii. Tetrapoda (bear limbs): four classes- Amphibia, Reptilia, Aves and mammals Superclass Pisces Class I – Cyclostomata (Circular Mouthed Fishes) • Characterised by circular and sucking mouth without jaws • Ectoparasites on fishes • 6-15 pairs of gill slits • Scales and fins are absent • Cartilaginous vertebral column and cranium • Closed type circulation • Marine but migrate to freshwater for spawning where they die, larvae after metamorphosis come back to the ocean • Examples: Petromyzon (Lamprey), Myxine (Hagfish) Class 2 - Chondrichthyes (Cartilaginous Fishes) General characters:- (1) Mostly marine and predaceous. (2) Body fusiform or spindle shaped. (3) Fins both median and paired, all supported by fin rays. (4) Skin tough containing minute placoid scales and mucous glands. (5) Endoskeleton entirely cartilaginous, without true bones (6) Notochord persistent. (7) Respiration by 5 to 7 pairs of gills. (8) Heart 2–chambered (1 auricle and 1 ventricle). (9) Kidneys opisthonephric. Excretion is ureotelic. (10) Brain with large olfactory lobes and cerebellum. Cranial nerves 10 pairs. Class 3 - Osteichthyes (Bony fishes) General Characters:- (1) Inhabit all sorts of water-fresh, brackish or salt; warm or cold. (2) Body spindle-shaped and streamlined. (3) Fins both median and paired, supported by fin rays of cartilage or bone. (4) Skin with many mucous glands, usually with embedded dermal scales of 3 types; ganoid, cycloid or ctenoid. (5) Endoskeleton chiefly of bone. (6) Respiration by 4 pairs of gills on body gill arches (7) Ventral heart 2-chambered (1 auricle + 1 ventricle). (8) Adult kidneys mesonephric. Excretion is ureotelic. (9) Brain with very small olfactory lobes, small cerebrum and well developed optic lobes and cerebellum. (10) Well developed lateral line system. Class Amphibia General characters:- (1) Aquatic or semi aquatic (freshwater), air and water breathing, carnivorous, cold–blooded, oviparous, tetrapod vertebrates. (2) Head distinct, trunk elongated. Neck and tail may be present or absent. (3) Pigment cells (chromatophores) present. (4) Exoskeleton absent. (5) Endoskeleton mostly bony. Notochord does not persist. Skull with 2 occipital condyles. (6) Respiration by lungs, skin and mouth lining. (7) Heart 3–chambered (2 auricles + 1 ventricle). (8) Kidneys mesonephric. Excretion is ureotelic. (9) Brain poorly developed. Cranial nerves 10 pairs. (10) Nostrils connected to buccal cavity. Class Reptilia General characters:- (1) Predominantly terrestrial, creeping or burrowing. (2) Body bilaterally symmetrical and divisible into 4 regions -head, neck, trunk and tail. (3) Limbs 2 pairs, pentadactyle. (4) Exoskeleton of horny epidermal scales, shields, plates and scutes. (5) Skin dry, cornified and devoid of glands. (6) Alimentary canal terminates into a cloacal aperture. (7) Endoskeleton bony. Skull is with one occipital condyle (monocondylar). (8) Heart usually 3–chambered, 4–chambered in crocodiles. (9) Respiration by lungs throughout life. (10) Kidney metanephric. Excretion is uricotelic. Class Aves General characters:- (1) Feather-clad, air-breathing, warm-blooded, oviparous, bipedal flying vertebrates. (2) Limbs are two pairs. (3) Exoskeleton is epidermal and horny. (4) Skin is dry and devoid of glands except the oil or preen gland at the root of tail. (5) Pectoral muscles of flight are well developed. (6) Skull smooth and monocondylic, bearing a single occipital condyle. Cranium large and dome-like. Sutures indistinct. (7) Vertebral column short. Centra of vertebrae heterocoelous (saddle-shaped). (8) Sternum large, usually with a vertical, mid ventral keel for attachment of large flight muscles. (9) Ribs double-headed (bicephalous) and bear posteriorly directed uncinate processes. (10) Both clavicles and single inter clavicle fused to form a V–shaped bone, called furcula wishbone. (11) Heart completely 4–chambered. There are neither sinus venosus or truncus arteriosus. Only right aortic (systemic) arch persists adult. Renal portal system vestigial. Blood corpuscles nucleated. (12) Birds are the first vertebrates to have was blood. Body temperature is regular (homoiothermous). (13) Respiration by compact, spongy, distensible lungs continuous with thin air-sacs. (14) Larynx without vocal cords. A sound box or syrinx, producing voice, lies at or near the junction of trachea and bronchi. (15) Kidneys metanephric and 3–lobed. Class Mammalia General characters:- (1) Hair-clad, mostly terrestrial, air-breathing, warm blooded, viviparous, tetrapod vertebrates. (2) Limbs 2 pairs, pentadactyle, each with 5 or fewer digits. (3) Exoskeleton includes lifeless, horny, epidermal hairs, spines, scales, claws, nails, hoofs, horns, bony dermal plates, etc. (4) Skin richly glandular containing sweat, sebaceous (oil) and sometimes scent glands in both the sexes. Females also have mammary glands with teats producing milk for suckling the young. (5) Endoskeleton thoroughly ossified. (6) Teeth are of several types (heterodont), borne is sockets (thecodont) and represented by two sets (diphyodont). (7) Respiration always by lungs (pulmonary). Glottis protected by a fleshy and cartilaginous epiglottis. Larynx contains vocal cords. (8) Heart 4-chambered with double circulation. (9) Sexes separate. (10) Fertilization internal preceded by copulation. (11) Mammals are viviparous, giving birth to living young ones. (12) Development uterine.

Notes Class 11 Biology Chapter 18 Neural Control and Coordination
https://acrobat.adobe.com/id/urn:aaid:sc:EU:6a8d8961-e33e-4b18-9a16-d355f864b874 Notes Class 11 Biology Chapter 18 Neural Control and Coordination Neural System The neural system is the control system of the body which consists of highly specialized cells called neurons. The sensory neurons detect and receive information from different sense organs (receptors) in the form of stimuli and transmit the stimuli to the Central Neural System (CNS) through sensory nerve fibers. In CNS the processing of information is done and a conclusion is drawn. The conclusion is sent to different organs (effectors) through motor nerves. These effectors then show the response accordingly. The neural or nervous system is present in most of the multicellular animals. Its complexity increases from lower to higher animals. Invertebrates have relatively simpler nervous system than the vertebrates. Human Neural System The whole nervous system of human being is derived from embryonic ectoderm. The human neural system is divided into two parts (i) the Central Neural System (CNS) (ii) the Peripheral Neural System (PNS) The CNS includes the brain and the spinal cord and is the site of information processing and control. The PNS comprises of all the nerves of the body associated with the CNS (brain and spinal cord). The nerve fibres of the PNS are of two types (a) Afferent Fibres They transmit impulses from tissues/organs to the CNS. (b) Efferent Fibres They transmit regulatory impulses from the CNS to the concerned peripheral tissues/organs. The PNS is divided into two divisions i.e., somatic neural system and autonomic neural system. The somatic neural system relays impulses from the CNS to skeletal muscles while, the autonomic neural system transmits impulses from the CNS to the involuntary organs and smooth muscles of the body. The autonomic neural system is further classified into sympathetic neural system and parasympathetic neural system. Neuron (Structural and Functional Unit of Neural System) Neurons are the longest cells in the body. Human neural system has about 100 billion neurons. Majority of the neurons occur in the brain. Fully formed neurons never divide and remain in interphase throughout life. A neuron is a microscopic structure composed of three major parts 1. Cell Body (Cyton or Soma) Like a typical cell it consists of cytoplasm, nucleus and cell membrane. The cytoplasm has typical cell organelles like mitochondria, Golgi apparatus, rough endoplasmic reticulum, ribosomes, lysosomes, certain granular bodies, neurofibrils, neurotubules and Nissl’s granules. Presence of neurofibrils and Nissl’s granules is the characteristic to all neurons. Neurofibrils play a role in the transmission of impulses. 2. Dendrites (Dendrons) Dendrites are usually shorter, tapering and much branched processes that project out of the cell body. They also contain Nissl’s granules and may be one to several in number. They conduct nerve impulses towards the cell body and are called afferent processes (receiving processes). 3. Axon Axon is a single, usually very long process of uniform thickness. The part of cyton from where the axon arises is called axon hillock (most sensitive part of neuron). The axon contains neurofibrils and neurotubules but does not have Nissl’s granules, cell organelles and granular bodies. The axon ends (distal end) in a group of branches, the terminal arborization (axon terminals). When terminal arborisations of the axon meet the dendrites of another neuron to form a synapse, each branch terminates as a bulb-like structure called synaptic knobs, which possess mitochondria and secretory vesicles (containing chemicals called neurotransmitters). The axons transmit nerve impulses away from the cell body to a synapse or to a neuromuscular junction. There are two types of axon a. Myelinated In myelinated nerve fibres Schwann cells form myelin sheath around the axon. The gaps between two adjacent myelin sheaths are called nodes of Ranvier. Myelinated nerve fibres are found in cranial and spinal nerves. b. Non-myelinated In non-myelinated nerve fibres Schwann cell does not form myelin sheath around the axon and are without nodes of Ranvier. They are commonly found in autonomous and somatic neural systems. Types of Neurons on the Basis of Structure Based on the number of axon and dendrites, the neurons are divided into three types (i) Multipolar neurons These neurons have several dendrites and an axon. They are found in cerebral cortex. (ii) Bipolar neurons These neurons have one dendrite and one axon. They are present in the retina of eye. (iii) Unipolar neurons These neurons have cell body with one axon only. These are found usually in the embryonic stage. Main Properties of Neural Tissue The neural tissue has two outstanding properties (a) Excitability It is the ability of nerve cells to generate an electrical impulse in response to a stimulus by altering the normal potential difference across their plasma membrane. (b) Conductivity It is the ability of nerve cells to rapidly transmit the electrical impulse as a wave from the site of its origin along their length in a particular direction. Functions of Neural System The nervous system serves the following important functions (i) Control and coordination Nervous system controls and coordinates the working of all parts of the body so that it functions as an integrated unit. This is achieved by three overlapping processes, i.e., sensory input, integration and motor output. (ii) Memory Nervous system stores the impressions of previous stimuli and retrieves (recalls) these impressions in future. These impressions are referred to as the experiences or memory. (iii) Homeostasis Nervous system helps in the maintenance of the body’s internal environment, i.e., homeostasis. Generation and Conduction of Nerve Impulse Nerve impulse is a wave of bioelectric/electrochemical disturbance that passes along a neuron during conduction of an excitation. Impulse conduction depends upon (i) Permeability of axon membrane (axolemma). (ii) Osmotic equilibrium (electrical equivalence) between the axoplasm and Extracellular Fluid (ECF) present outside the axon. The generation of a nerve impulse is the temporary reversal of the resting potential in the neuron. It occurs in following three steps Polarisation (Resting Potential) In a resting nerve fibre (a nerve fibre that is not conducting an impulse), the axoplasm (neuroplasm of axon) inside the axon contains high concentration of K+ and negatively charged proteins and low concentration of Na+. (i) In contrast, the fluid outside axon contains a low concentration of K+ and a high concentration of Na+ and thus form a concentration gradient. (ii) These ionic gradients across the resting membrane are maintained by the active transport of ions by the sodium-potassium pump, which transports 3Na+ out wards and 2K+ inwards (into the cell). (iii) As a result, the outer surface of the axonal membrane possesses a positive charge, while its inner surface becomes negatively charged and therefore, is polarised. (iv) The electrical potential difference across the resting plasma membrane is called as the resting potential. The state of the resting membrane is called polarised state. Depolarisation (Action Potential) When a stimulus of adequate strength (threshold stimulus) is applied to a polarised membrane, the permeability of the membrane to Na+ ions is greatly increased at the point of stimulation (site A). (i) This leads to a rapid influx of Na+ followed by the reversal of the polarity at that site, i.e., the outer surface of the membrane becomes negatively charged and the inner side becomes positively charged. The polarity of the membrane at the site A is thus, reversed and said to be depolarised. (ii) The electrical potential difference across the plasma membrane at the site A is called the action potential, another name of nerve impulse. (iii) At adjacent sites, e.g., site B, the membrane (axon) has positive charge (still polarised) on the outer surface and a negative charge on its inner surface. (iv) The stimulated negatively charged point on the outside of the membrane sends out an electrical current to the positive point next to it. As a result, a current flows on the outer surface from site B to site A, while on the inner surface current flows from site A to site B. This process (reversal) repeats itself over and over again and a nerve impulse is conducted through the length of the neuron. Re-polarization (i) The rise in the stimulus-induced permeability to Na+ is extremely short-lived. It is quickly followed by a rise in permeability to K+. (ii) Within a fraction of a second, Na+ influx stops and K+outflow begins until the original resting state of ionic concentration is achieved. Thus, resting potential is restored at the site of excitation, which is called repolarisation of the membrane. This makes the fibre once more responsive to further stimulation. (iii) In fact until repolarisation occurs neuron cannot conduct another impulse. The time taken for this restoration is called refractory period. There are mainly two types of synapses Electrical Synapses (i) The membranes of pre and post-synaptic neurons are in very close proximity (i.e., in continuity). The continuity is provided by the gap junction (small protein tubular structures) between the two neurons. (ii) In electrical synapse, there is minimal synaptic delay because of the direct flow of electrical current from one neuron into the other across these synapses. Thus, impulse transmission across an electrical synapses is always faster than that across a chemical synapse. In such synapses, transmission of impulse is very similar to impulse conduction along a single axon. (iii) Electrical synapses are rarely found in our system. It is found in cardiac muscle fibres, smooth muscle fibres of intestine and the epithelial cells of lens. Chemical Synapses The membranes of pre- and post-synaptic neurons are separated by a fluid-filled space called synaptic cleft. A brief description of the mechanism of synaptic transmission is given below (i) When an impulse (action potential) arrives at a pre-synaptic knob, calcium ions from the synaptic cleft enter the cytoplasm of the pre-synaptic knob. (it) The calcium ions cause the movement of the synaptic vesicles to the surface of the knob. The synaptic vesicles are fused with the pre-synaptic (plasma membrane and get ruptured (exocytosis) to discharge their contents (neurotransmitter) into the synaptic cleft. (iii) The neurotransmitter of the synaptic cleft binds with specific protein receptor molecules, present on the post-synaptic membrane. (iv) This binding action changes the membrane potential of the post-synaptic membrane, opening channels in the membrane and sodium ions to enter the cell. This causes the depolarisation and generation of action potential in the post-synaptic membrane. Thus, the impulse is transferred to the next neuron. (v) The new potential developed may be either excitatory or inhibitory. Human Nervous System The human neural system can be categorized to (a) Central Nervous System (CNS) (b) Peripheral Nervous System (PNS) Central Nervous System (CNS) It is the integrating and command centre of the nervous system which consists of the brain and spinal cord (as discussed earlier). Brain The brain is the central information processing organ of our body and acts as the ‘command and control system’. It controls the following activities (i) The voluntary movements and balance of the body. (ii) Functioning of vital involuntary organs, e.g., Lungs, heart, kidneys, etc. (iii) Thermoregulation, hunger and thirst. (iv) Circardian (24 hrs) rhythms of our body. (u) Activities of several endocrine glands and human behaviour. (vi) It is also the site for processing of vision, hearing, speech, memory, intelligence, emotions and thoughts. Location The brain is the anterior most part of the central neural system, which is located in the cranium (cranial cavity) of the skull. Protective Coverings of the Brain It is covered by three membranes or meninges (cranial meninges) (i) The outermost membrane, the duramater is the tough fibrous membrane adhering close to the inner side of the skull. (ii) The middle very thin layer called arachnoid membrane (arachnoid mater). (iii) The innermost membrane, the piamater is thin, very delicate, which is in contact with the brain tissue. i. The forebrain It consists of Olfactory lobes The anterior part of the brain is formed by a pair of short club-shaped structures, the olfactory lobes. These are concerned with the sense of smell. Cerebrum It is the largest and most complex of all the parts of the human brain. A deep cleft divides the cerebrum longitudinally into two halves, which are termed as the left and right cerebral hemispheres connected by a large bundle of myelinated fibres the corpus callosum. * The outer cover of cerebral hemisphere is called cerebral cortex. The cerebral cortex is referred to as the grey matter due to its greyish appearance (as neuron cell bodies are concentrated here). The cerebral cortex is greatly folded. The upward folds, gyri, alternate with the downward grooves or sulci. Beneath the grey matter there are millions of medullated nerve fibers, which constitute the inner part of the cerebral hemisphere. The large concentration of medullated nerve fibres gives this tissue an opaque white appearance. Hence, it is called the white matter. * Lobes A very deep and a longitudinal fissure, separates the two cerebral hemispheres. Each cerebral hemisphere of the cerebrum is divided into four lobes, i.e., frontal, parietal, temporal and occipital lobes. In each cerebral hemisphere, there are three types of junctional areas * Sensory areas receive impulses from the receptors and motor areas transmit impulses to the effectors. * Association areas are large regions that are neither clearly sensory nor motor in junction. They interpret the input, store the input and initiate a response in light of similar past experience. Thus, these areas are responsible for complex functions like memory, learning, reasoning and other intersensory associations. Distinction the posterioventral part of forebrain. Its main parts are as follows * Epithalamus is a thin membrane of non-nervous tissue. It is the posterior segment of the diencephalon. * The cerebrum, wraps around a structure called thalamus, which is a major coordinating center for sensory and motor signaling. The hypothalamus, that lies at the base of thalamus contains a number of centers, which control body temperature, urge for eating and drinking. It also contains several groups of neurosecretory cells, which secrete hormones called hypothalamic hormones. The inner parts of cerebral hemispheres and a group of associated deep structures like amygdala, hippocampus, etc., form a complex structure (limbic lobe or limbic system) that are involved in the regulation of sexual behaviour,expression of emotional reactions, e.g„ excitement, pleasure,rage and fear and motivation, ii. Midbrain The midbrain is located between the thalamus hypothalamus of the forebrain and pons of the hindbrain. A canal called the cerebral aqueduct passes through, the midbrain. The dorsal portion of the midbrain mainly consists of two pairs (i.e., four) of rounded swellings (lobes) called corpora quadrigemina. iii. Hindbrain The hindbrain consists of (a) Pons consists of fibre tracts that interconnect different regions of the brain. (b) Cerebellum is the second largest part of the human brain (means litde cerebrum). It has very convoluted surface in order to provide the additional space for many more neurons. (c) Medulla (oblongata) is connected to the spinal cord and contains centers, which control respiration, cardiovascular reflexes and gastric secretions. Spinal Cord (i) It forms the posterior part of the CNS, running mid-dorsally in the neural canal of the vertebral column. In an adult, the spinal cord is about 42-45 cm long. Its diameter varies at different levels. (ii) The spinal cord is formed of two types of nervous tissue, i.e., grey matter and white matter. (iii) The grey matter is surrounded by white matter, which consists of groups of myelinated axons. (iv) The spinal nerve tracts are divisible into two, ascending (conducting sensory impulses towards brain) and descending (conducting motor impulses from brain). (v) Spinal cord conducts impulses to and from the brain and controls most of the reflex activities and provides a means of communication between spinal nerves and the brain. Reflex Action and Reflex Arc The entire process of response to a peripheral nervous stimulation, that occurs involuntarily, i.e., without conscious effort or thought and requires the involvement of a part of the central nervous system is called a reflex action. The nervous pathway taken by nerve impulses in a reflex action is called reflex arc. Types of Reflexes Reflexes are categorized into two (i) Unconditioned (inborn reflexes and transmitted through heredity) breast feeding and swallowing. (ii) Conditioned (acquired after birth, i.e., adopted during the course of life time.) e.g., Withdrawl of a body part (like limb) which comes in contact with objects that are extremly hot, cold, pointed or animals that are scary or poisonous. Mechanism of Reflex Action (i) The reflex pathway comprises atleast, one afferent (receptor) neuron and one efferent (effector) neuron arranged in a series. (ii) The afferent neuron receives signal from a sensory organ and transmits the impulse via a dorsal nerve root into the CNS (at the level of spinal cord). (iii) The efferent neuron then carries signals from CNS to the effector. The stimulus and response in this way forms a reflex arc, e.g., Knee jerk reflex as shown above in the diagram. Peripheral Nervous System (PNS) The peripheral nervous system consists of 1. Somatic Neural System (SNS) 2. Autonomic Neural System (SNS) 1. Somatic Neural System The somatic neural system contains nerves which relay impulses from CNS to skeletal muscles. These can be further categorized into cranial (from brain) and spinal nerves on the basis of their origin. i.Cranial Nerves These nerves emerge specifically from the forebrain and brain stem. ii. Spinal Nerves All spinal nerves are mixed, having sensory and motor fibres in approximately equal numbers. In humans, 31 pairs of spinal nerves are present as Cervical (8 pairs), Thoracic (12 pairs), Lumber (5 pairs), Sacral (5 pairs), Coccygeal (1 pair). Based on their functions, the nerve fibres of PNS are divided into two groups, i.e., afferent fibres and efferent fibres. The afferent nerve fibres transmit sensory impulses from tissues/organs to the CNS and form the sensory or afferent pathway. The efferent nerve fibres transmit motor impulses from CNS to the concerned tissues/organs and form the motor or efferent pathways. 2. The Autonomic Neural System (ANS) The autonomic neural system consists of the sympathetic and parasympathetic nervous system. The former is called thoraco-lumber outflow and the latter is called craniosacral outflow depending upon their origin. Sensory Reception and Processing The sensory organs (receptors) enable us to detect all types of changes in the environment and send appropriate signals to the CNS, where all the inputs are processed and analaysed. Signals are then sent to different centers of the brain. The most complex sensory receptors consist of numerous sense cells, sensory neurons and associated accessory structures. For example, eye (sensory organ for vision) and the ear (sensory organ for hearing). Eye The organ of sight are a pair of eyes in human. Position The eyes are situated in the deep protective bony cavities, called the orbits or eye sockets of the skull. Parts of an Eye The adult human eye ball is nearly spherical in structure. It consists of tissues present in three concentric layers (i) Outermost fibrous layer composed of sclera and cornea. (ii) Middle layer consists of choroid, ciliary body and iris. (iii) Innermost layer consists df retina. Outermost Layer (i) Sclera is an opaque outermost covering, composed of dense connective tissue that maintains the shape of the eyeball and protects all the inner layers of the eye. (ii) Cornea is a thin transparent, front part of sclera, which lacks blood vessels but is rich in nerve endings. Middle Layer (i) Choroid is a pigmented layer (bluish) present beneath the sclera. It contains numerous blood vessels and nourishes the retina. The choroid layer is thin over the posterior two-thirds of the eye ball, but it becomes, thick in the anterior part to form the ciliary body. (ii) The eye ball contains a transparent crystalline structure called lens. Ciliary body holds the lens in position, stretching and relaxation of ciliary body changes the focal length of the lens for accommodation. (iii) Iris forms a pigmented circle of muscular diaphragm attached to the ciliary body in front of the lens. Its pigment gives eye its colour. The movement of muscle fibres of iris controls the size (diameter) of pupil. (iv) Pupil is the aperture surrounded by the iris. It contains two types of smooth muscles, circular muscles (sphincters) and radial muscles (dilators) of ectodermal origin. (v) Sympathetic stimulation causes the radial muscles to contract and the pupil to dilate or get larger. Parasympathetic stimulation causes the circular muscles to contract and the pupil to constrict. Inner Layer The inner layer is the retina and it contains three layers of cells from inside to outside, i.e., ganglion cells, bipolar cells and photoreceptor cells. The photoreceptors or visual cells are of two types, i.e., rods (rod cells) and cones (cone cells). Both of these cells contain light sensitive proteins called the photopigments. The twilight (scotopic) vision is the function of the rods. These cells contain a purplish-red protein called the rhodopsin (visual purple), which contains a derivative of vitamin-A. The daylight (photopic) vision and colour vision are functions of cones. There are three types of cones, which possesses characteristic photopigments that respond to red, green and blue lights. The sensation of different colours are produced by various combinations of these cones and their photopigments. In case of equal stimulation of these cones, a sensation of white light is produced. Optic Nerves The optic nerves are connected with the brain. These nerves leave the eye and the retinal blood vessels enter it at a point medial to and slightly above the posterior pole of the eye-ball. Photoreceptor cells (rods and cones) are not present in that region and hence, it is called blind spot, as no image is formed at this spot. Macula Lutea and Fovea Centralis At the posterior pole of the eye lateral to the blind spot, there is a small oval, yellowish area of the retina called the macula lutea or yellow spot, which has at its middle a shallow depression, the fovea centralis (fovea). The fovea is a thinned out portion of the retina where only the cones are densly packed. It is the point where the visual acuity (resolution) is the greatest. Contents of the Eye (i) Aqueous Humour The space between the cornea and lens is called the aqueous chamber, which contains a thin watery fluid called aqueous humour. (ii) Vitreous Humour The space between the lens and retina is called the vitreous chamber, which is filled with a transparent get called the vitreous humour. Mechanism of Vision In human eyes, the vision is called binocular vision (i.e., both the eyes can be focused on a common object). (i) Retina receives light rays (in visible wavelength) through the cornea and lens generate impulses in rods and cones. (ii) The photosensitive compounds (photopigments) in the human eye are composed of opsin (a protein) and retinal (an aldehyde of vitamin-A). (iii) The received light induces dissociation of the retinal from opsin resulting in changes in the structures of the opsin. This causes the changes in the permeability of membrane. As a result, the potential differences are generated in the photoreceptor cells. This produces a signal that generates action potential in the ganglion cells through the bipolar cells. (iv) These impulses (action potentials) are transmitted by the optic nerves to the visual cortex of the brain. (v) In brain, neural impulses are analaysed and the image formed on the retina is recognised (based on earlier memory and experience). Common Diseases (i) Cataract This is a eye disease generally occur in older people (above 60 years). Lens becomes opaque due to disease or ageing. It leads to blindness. It can be corrected by wearing suitable glasses or by replacing the defective lens with a normal lens from a donor. (ii) Myopia (near or short sightedness) It occurs due to convexity of lens or longer eye ball, which results in an image of distant objects being formed in front of the retina, and can be corrected by wearing spectables or concave lenses. (iii) Hypermetropia (far or long sightedness.) The image of nearer object becomes blurred. It is due to image being formed beyond the retina due to eye ball being short or lens being flattened. It can be corrected by wearing convex or convergent lenses. (iv) Presbiopia It generally occurs after 40 years. The loss of elasticity in the eye lens occurs so that near objects (written or printed words) are not correcdy visible. It can be correct’d by convex/bifocal lenses. Ear Ears are a pair of statiocoustic organs meant for both sensory functions, i.e., hearing and maintenance of body balance. Position The ears are located on the sides of the head. In most mammals, the ear is a flap of tissue also called pinna. It is a part of auditory system. The mammalian ear can be anatomically divided into three major sections 1. External Ear The external ear consists of pinna and the auditory canal (external auditory meatus), which collect sound waves and channel them to tympanic membrane (ear drum) separating the outer ear from the middle ear. The auditory canal leads inwards and extends upto the tympanic membrane (the ear drum). There are very fine hairs and wax-secreting sebaceous glands in the skin of the pinna and the meatus. The tympanic membrane is composed of connective tissues covered with skin outside and with mucus membrane inside. 2. Middle Ear The middle ear contains three ossicles called malleus (hammer), incus (anvil) and stapes (stirr-up), which are attached to one another in a chain-like fashion. The malleus is attached to the tympanic membrane and the stapes is attached to the oval window (a membrane beneath the stapes) of cochlea. These ossicles increase the efficiency of transmission of sound waves to the inner ear. The middle ear also opens into the Eustachian tube, which connects with the pharynx and maintains the pressure on either sides of the ear drum. It also enables you to ‘pop’ your ears when you change altitude. 3. Inner Ear The inner ear consist of a labyrinth of fluid-filled chambers within the temporal bone of the skull. The labyrinth consists of two parts the bony and membranous labyrinths. The bony labyrinth is a series of channels. Inside the channels, membranous labyrinth lies, which is surrounded by a fluid called perilymph. The membranous labyrinth is filled with a fluid called endolymph. The coiled portion of the labyrinth is called cochlea. The membranes constituting cochlea (the Reissner’s and basilar), divide the bony labyrinth into two large canals, i.e., an upper vestibular canal (scala vestibuli) and a lower tympanic canal (scala tympani). These (both) canals are separated by a small cochlear duct called scala media. The vestibular and tympanic canals contain and the cochlear duct is filled with endolymph. At the base of the cochlea, the scala vestibuli ends at the oval window while, the scala tympani terminates at the round window, which opens to the middle ear. Organ of Corti The floor of the cochlear duct, the basilar membrane bears the organ of Corti. It contains the mechanoreceptors of the ear. The hair cells are present in rows on the internal side of the organ of Corti, that act as auditory receptors. The basal end of the hair cell is in close contact with the afferent nerve fibres. A large number of processes called stereo cilia are projected from the apical part of each hair cell. Above the rows of hair cells is a thin elastic membrane called tectorial membrane. Vestibular Apparatus (i) The inner ear also contains a complex system called vestibular apparatus (located above the cochlea). It is composed of three semicircular canals and the otolith organ consisting of the saccule and utricle. (ii) Each semicircular canal lies in a different plane at right angles to each other. The membranous canals are suspended in the perilymph of the bony canals. The base of canals is swollen and is called ampulla, which contains a projecting ridge called crista ampullaris, which has hair cells. (iii) The saccule and utricle contain a projecting ridge called macula. The crista and macula are the specific receptors of the vestibular apparatus responsible for the maintenance of balance of the body and posture. Mechanisms of Hearing (i) Sound waves from the environment are received by the external ear and it directs them to the ear drum. (ii) The ear drum vibrates due to sound waves and the vibrations are send to oval window through the ear ossicles (malleus, incus and stapes). (iii) The vibrations are passed through the oval window on to the fluid of the cochlea, where they generate waves in the lymph. (iv) The waves in the lymph induce a ripple in the basilar membrane. (v) These movements of the basilar membrane bend the hair cells, pressing them against the tectorial membrane. Due to this, the nerve impulses are generated in the associated afferent neurons. These impulses are transmitted by the afferent fibres via auditory nerves to the auditory cortex of the brain, where the impulses are analaysed and the sound is recognised. Common Diseases (i) Meniere’s Syndrome It is a hearing loss due to pathological distension of membranous labyrinth. (ii) Eustachitis It occurs due to inflammation of Eustachian tube. (iii) Tympanitis It is due to inflammation of ear drum. (iv) Otalgia Pain occurs in ear. (v) Otitis media Acute infection in middle ear.

Notes on LOCOMOTION AND MOVEMENT
https://acrobat.adobe.com/id/urn:aaid:sc:EU:9b112541-879a-4b2f-9583-b5ff0e0604fd LOCOMOTION AND MOVEMENT Movement Movement is defined as any visible change of position, exhibited either by the whole organism or any part of the body. It is one of the important characteristics of living organisms. The movement of living things are autonomic (self-sustained) while, the movement of non-living objects is induced (due to external forces). Both animals and plants exhibit wide range of movements. Movement of animals can be muscular and non-muscular. Plants show cellular and often organ movement, but not the movement of the organism. Types of Movement Three main types of movement are exhibited by the cells of the human body. These are as follows 1. Amoeboid (Pseudopodial) Movement Movement with the help of finger-shaped protoplasmic extensions (i.e., pseudopodia or false feet) (as seen in Amoeba) is called amoeboid movement, e.g., Movement of leucocytes and macrophages in blood. Cytoskeletal elements, like microfilaments are also involved in this type of movement. 2. Ciliary Movement Movement with the help of cilia is called ciliary movement. Cilia are short, fine, hair-like structures present all over the body surface in large numbers, which beat in succession in coordinated manner to help in locomotion, e.g., Removal of dust particles and foreign substances through the trachea, passage of ova through female reproductive tract. This type of movement occurs in most of our internal tubular organs that are lined by ciliated epithelium. The above two movements are called non-muscular movements. 3. Muscular Movement Movement with the help of muscles is called muscular movement. These are brought about by the movement of myofilaments packed within the muscle fibres. The contractile property of muscles is used effectively to bring about a movement. This type of movement is found in majority of multicellular animals including humans. Locomotion It is the movement of an animal as a whole from one place to another. These are vpluntary movements that results in change of place or location. It requires a perfect coordinated activity of muscular, skeletal and neural system. Locomotion takes several forms such as walking, running, flying, swimming, etc. Advantages of Locomotion It helps the animal in search of food, shelter, mate, to escape from enemies/predators, to locate suitable areas for breeding or to disperse to new locations. Methods of locomotion in animals vary with their habitats and the demand of situation. Locomotion v/s Movement It is very difficult to separate movement from locomotion because an animal cannot change its place (locomotion) without movement, e.g., Cilia helps in movement of food inside cytopharynx and in locomotion in Paramecium. Tentacles in Hydra are used for capturing prey and in locomotion. Limbs are used for change of body postures as well as for locomotion in humans. This suggests that movements and locomotion are interlinked thus, stating that all locomotion are movements but all . movements are not locomotion. Muscles These are made up of highly specialized thin and elongated cells called muscle fibres. Muscles arises from the embryonic mesoderm. It makes about 40-50% of a human body weight. Special Properties Muscles exhibit various special properties, some of them are given below (i) Contractibility The cells of muscle can be shorten considerably and return to the original relaxed state. (ii) Excitability It is due to the energy stored in the electrical potential difference across the plasma membrane. Other distinguishing properties are extensibility and elasticity. NOTE: * Muscle Tissue is the most abundant tissue in most animals. * Human body has some 639 separate muscles that bring about movement in majority of animals. * The study of muscle is called Myology. • Muscles of iris and ciliary body are ectodermal in origin. • The largest/biggest muscle in human body is gluteus maximus (hip muscle), the longest muscle is sartorius (back muscle), the strongest muscle is masseter (jaw muscles). • The longest smooth muscle is rectus abdomins and the shortest muscle is stapedial muscle. TYPES OF MUSCLES Muscles have been classified using different criteria, i. e., location, appearance and nature of regulation of their activities. Based on their location, the muscles are of three types, i.e., skeletal, visceral and cardiac. i. Skeletal or Striated Muscles It functions in association with the skeleton of organism. Under the microscope, they have a striped appearance and hence are called striated muscles. They are also known as voluntary muscles as their activities are under the voluntary control of the nervous system. The major component of muscles is water and potassium is the most abundant mineral element. They are primarily involved in locomotory actions and change of body postures. ii. Visceral or Smooth Muscles They are found in the inner walls of hollow visceral (internal) organs of body like alimentary canal, reproductive tract, etc. They do not exhibit any striation, i.e., smooth in appearance and hence, are called smooth muscles (non-striated muscle). They are also known as involuntary muscles as they are not under the voluntary or direct control of the nervous system.They assist in the transportation of materials, e.g., Movement of food through the digestive tract and gametes through the genital tract. iii. Cardiac Muscles It occurs in the wall of the heart and in walls of large veins (e.g., Pulmonary veins and superior vena cava), where these veins enter the heart. These are striated and involuntary in nature. Oblique bands and intercalated discs are their characteristic feature. It assembles in a branching pattern to form a cardiac muscle. They never get fatigued. NOTE: * Two types of muscles fibres are found in the body. Slowtwitch (in muscles that require endurance) and fast twitch (in muscles that contract quickly.) * High intensity exercise causes an increase in muscle mass, while low intensity exercise, aerobic exercise, build mass, but do not burn colonies. DETAILED STRUCTURE OF A SKELETAL MUSCLE: Skeletal muscle is made up of a numbed of muscle bundles or fascicles held together by fascia (collagenous connective tissue layer)(plasma membrane) and contains well developed endoplasmic reticulum (sarcoplasmic reticulum), specialised for calcium storage in its sarcoplasm (cytoplasm).Muscle fibre is a syncitium as the sarcoplasm contains many nuclei. There are large number of parallely arranged filaments called myofilaments or myofibrils (characteristic feature of muscle fibre). DETAILED STUDY OF A MYOFIBRIL A myofibril has alternate dark and light bands. The dark bands are also called A-band (anisotropic band) and contains protein myosin. The light bands are also called I-band (isotropic band) and contains actin. The striated appearance of myofibril is due to the distribution pattern of the proteins actin and myosin. Both these proteins are arranged as rod-like structures, parallel to each other and also to longitudinal axis of myofibrils. Actin filaments are thinner than myosin filaments, hence are usually called thin and thick filaments respectively. Composition of Muscle Bundle Each muscle bundle contains a number of muscle fibres (muscle cells), bounded by sarcolemma Each I-band has its centre, a dark membrane called Z-line (an elastic fibre). It is also called Z- disc or Krause’s membrane or Dobie’s line. The part of the myofibril between two successive Z-lines is a called a sarcomere (functional unit of contraction). A sarcomere consists of the A-band and half of each adjacent I-band. A thin fibrous membrane called M-line present in the middle of A-band holds the thick filaments together. The A and I-bands are arranged alternately throughout the length of myofibril. At the centre of A-band, a portion is present that is not overlapped by thin filaments. It is called the H-zone (Hensen zone).In resting state, the edges of thin filaments on either side of thick filaments partially overlap each other leaving H-zone in the centre of thick filaments. STRUCTURE OF CONTRACTILE PROTEINS The thick myofilaments are formed by myosin protein. The thin myofilaments are formed by three types of proteins called actin, tropomyosin and troponin. These four proteins are collectively known as contractile proteins. Thick Myofilament or Primary Myofilament It consists mainly of myosin protein. Each myosin filament is a polymerized protein, made up of many monomeric proteins called meromyosins. Each meromyosin has two important parts as follows Globular Head It has a short arm, called heavy meromyosin (HMM). The HMM components projects outwards at regular distance and angle from each other, from surface of a polymerized myosin filament and known as cross arm. The globular head is an active ATPase enzyme, which has binding sites for ATP and active sites for actin. Tail Tail is called the light meromyosin (LMM). The myosin molecule has two identical heavy chains and four light chains. The two heavy chairis wrap spirally around each other to form a double helix. The light chains are the parts of the myosin heads and help control the function of head during the contraction of muscle. Thin Myofilament or Secondary Myofilament It is composed of following proteins Actin It is a globular protein with low molecular weight. It is made up of two ‘F’ (filamentous) actin helically wound to each other. Each F actin is a polymer of monomeric ‘G’ (globular) actins. Tropomyosin Two filaments of. this protein run close to the ‘F’ actions throughout its length. iii. Troponin It is a complex protein of three globular peptides (Troponin T, Troponin-I and Troponin-C) distributed at regular intervals on tropomyosin. In the resting stage of muscle fibre, a subunit of troponin masks the active sites for myosin on the actin filaments. NOTE: * Partial overlapping of primary myofilaments by the secondary myofilaments imparts dark appearance to the A-bands. * The strong affinity of the troponin for calcium ions is believed to initiate the contraction process. MECHANISM OF MUSCLE CONTRACTION The contraction of muscle is best explained by the sliding filament theory. It states that contraction of muscles takes place by the sliding of thin and thick filaments that past over each other with the help of cross-bridge to reduce the length of the sarcomere. This theory was proposed independendy by AF Huxley and R Niedergerke and by HE Huxley and Jean Manson in England in 1954. 1. The sequence of events leading to contraction is initiated by a signal in the Central Nervous System (CNS), either from the brain (voluntary activity) or from spinal cord (reflex activity) via a motor neuron. 2. A motor neuron along with the muscle fibres connected to it, forms a motor unit and the action potential is conveyed to a motor end plate (or neuromuscular junction) i.e., the junction between a motor neuron and sarcolemma of muscle fibre) on each muscle fibre. 3. A neurotransmitter (acetylcholine) is released at the junction by the neural signal which generates an action potential in the sarcolemma. This spreads and causes the release of calcium ions into sarcoplasm. Calcium plays a key regulatory role in muscle contraction. Increase in calcium ions level leads to their binding to troponin subunit. Thus, exposing the active sites on F-actin molecules. Formation of Cross-Bridge 4. An ATP molecule joins the active site on myosin head of myosin myofilament. These heads contains an enzyme, myosin ATPase that along with Ca2+ and Mg2+ ions catalyses the breakdown of ATP. 5. The energy is transferred to myosin head, which energises and straightens to join an active site on actin myofilament, forming a cross bridge. 6. The energized cross-bridges move, causing the attached actin filaments to move towards the centre of A-band. The Z-line is also pulled inwards causing shortening of sarcomere, i.e„ contraction. It is clear from the above explanation that during contraction A-bands retain the length, while I-bands get reduced. 7. The myosin head releases ADP and Pi, relaxes to its low energy state. The head detaches from actin myofilaments when new ATP joins it (cross-bridge broken). 8. In repeating cycle, the free head cleaves the new ATP. The cycles of cross bridge formation and breakage is repeated causing further sliding. MUSCLE RELAXATION After contraction the calcium ions are pumped back to the , sarcoplasmic cisternae, blocking the active sites on actin myofilaments. The Z-line returns to original position, i.e., relaxation. NOTE: Rigor Mortis is the state of body stiffening after death due to non-separation of actin and myosin filaments caused by non-availability of ATP. It appears first in the small muscles of the face (such as jaw) and those being used most actively prior to death. It persists till decomposition starts. Red and White Birds and mammals have two kinds of striated muscle fibres, in their skeletal muscles, i.e., red (or slow) and white (or fast) muscle fibres. Differences between Red and White Muscle Fibres SKELETON (SKELETAL SYSTEM) The hard, supportive or protective elements of the animal body constitute the skeletal system or skeleton. It consists of a framework of bones and a few cartilages. Both of them are specialized connective tissues. Bone has a very hard matrix due to calcium salts and made up of a protein called ossein. Cartilage has slightly pliable matrix due to chondroitin salts. It is made up of a protein called chondrin. Bone consists of a dense outer layer known as compact bone and spongy layer inside called spongy bone. Bones are remodeled for strength when exposed to new stresses. Functions of Skeleton Skeleton serves to perform following functions (i) Support It gives support to softer body parts. (ii) Protection It protects the delicate internal organs like brain, heart, lungs, etc. (iii) Muscle attachment Provide surface for attachment of muscles. (iv) Movement Bones helps in bringing about movements also. (v) Blood cell formation To manufacture blood corpuscles in bone marrow. (vi) Helps in breathing and hearing Tracheal rings, sternum and ribs are helpful in breathing, while ear bones (middle ear) transmit sound vibrations. Human Skeleton Human body is made of 270 bones, which are fused variously to form 206 bones. On the basis of the position of the skeletal structures in the body, the endoskeleton is divisible into two parts (i) Axial skeleton It comprises of 80 bones, which includes skull, vertebral column, ribs and sternum. (ii) Appendicular skeleton It lies along the transverse (side) axis. It comprises of 126 bones, which , includes pectoral and pelvic girdles and limb bones, i.e., bones of arms and legs). NOTE: * Bones are of four categories according to size and shape, i.e., long, short, flat and irregular bones. * Smallest bone is Stapes. * Longest and strongest bone is Femur. * Funny bone is Olecranon process on top of the ulna. * There are remarkable differences in the skull of male and female, thus, together with the pelvis it is used for identification of sex. Skull It is the bony framework of the head. It is composed of two set of bones (cranial and facial) that forms total of 22 bones [bones of middle ear (6 bones) and hyoid bone (1) are also included in bones of skull]. Bones of skull are as follows (i) Cranium — 8 includes frontal (1), parietal (2), temporal (2), occipital (1), sphenoid (1), ethmoid (1). They form the hard protective outer covering (cranium) for the brain (ii) Facial bones — 14 includes maxillae (2), palatine (2) mandible (1), vomer (1), nasal (2), zygomatic (2), lacrimal (2), inferior turbinate (2) They form the front part of the skull (iii) Ear ossicles — 6 includes, 2 malleus, 2 incus, 2 stapes These three tiny bones belong to the middle ear. (iv) Hyoid A U-shaped bone present at the base of buccal cavity. It is the only bone which is not in contact with the another bone. This is also called tongue bone. Human skull is dicondylic, the skull region articulates with vertebral column with the help of two occipital condyles. Vertebral Column It is also called backbone or spine. It is dorsally placed, extending from the base of the skull and constitutes the main framework of the trunk. It is made of, 26 serially arranged units called vertebrae.lt includes cerical or yes bone (7), Thoracic (12), Lumbar (5), Scaral or Sacrum (1-fussed) and coccygeal (1-fused). The vertebral formula for humans is C7,T12,L5,S5,C(3-5). NOTE: * Altas is the first vertebra and it articulate with the occipital condyles. * The number of cervical vertebrae is 7 in almost all mammals). * Lumbar is the largest and the strongest in the vertebral column. Vertebral column performed following junctions (i) provides protection to the spinal cord, (ii) supports the head, (iii) allows flexion and bending of the back and body (iv) also serves as point of attachment for the ribs. Sternum It is a flat daggar-shaped bone located on the ventral midline of thorax. Ribs These are the thin, flat curved bones that form a protective cage around the organs of upper body. The ribs are composed of 24 bones arranged in 12 pairs, connected dorsally to thoracic vertebrae and ventrally to sternum by hyaline cartilage. It has two articulation surfaces on its dorsal end and hence called bicephalic. True Ribs The first seven ribs are attached directly with the sternum and are called true ribs. False Ribs The 8th, 9th and 10th pairs of ribs join the seventh rib with the help of hyaline cartilage. They do not articulate directly with sternum. Hence, are called vertebrochondral (false) ribs. Floating Ribs The last two (11th and 12th) pairs of ribs remains free anteriorly and are called floating ribs. (i) they protect the heart, large blood vessels and lungs. (ii) bear respiratory muscles. (iii) also lower two pairs of ribs also protect the kidneys. Thoracic vertebrae, ribs and sternum together form the rib cage. Limbs The bones of the limbs alongwith gridles constitute the appendicular skeleton. Each limb is made of 30 bones. Forelimb The bones of the hand (forelimb) constitutes Humerus (1), Radius (1), Ulna (1), Carpals/wrist bones (8), Metacarpals-palm bones (5) and phalanges/digits (14). The humerus and ulna together make up the below. The ulna is longer than the radius and connects more firmly to the humerus. The radius contributes to the movement of the wrist. The phalangeal formula for human hand is 2, 3, 3, 3, 3. Pectoral (Shoulder) Girdle It consists of following two bones, i.e., scapula and clavicle. i. Scapula (Shoulder Blade) It consists of a sharp ridge the spine and a triangular body. The end of spine projects as a flattened and expanded portion called acromion. This articulates with the clavicle. Glenoid cavity is a depression below the acromian to which head of humerus articulates forming shoulder joint. ii. Clavicle (Collar Bone) Each clavicle is a long slender bone with two curvatures. The clavicle helps in articulation of the upper limb with axial skeleton. This provides an attachment point for numerous muscles that allow shoulder and elbow joints to move. Hindlimb The bones of the leg (hindlimb) constitutes Femur (1), Tibia (1), Fibula (1), Tarsals (7), Metatarsals (5) and phalanges (14). A cup-shaped bone called patella cover knee ventrally. It is a seasmoid bone (bone embedded within a tendon). Femur, tibia and fibula bones together support the shank of leg. Tarsals form the ankle, metatarsals form the sole and phalanges form the digits of the foot. The phalangeal formula for human foot is 2, 3, 3, 3, 3. Pelvic (Hip) Girdle It is located in the lower part of the trunk. It consists of two coxal (hip) bones. Each coxal is also known as ossa coxae or innominate bone. This is formed by fusion of the following three bones (i) Upper ilium (ii) Lower ischium (iii) Inner pubis The innominate at the middle of its lateral surface has a deep, cup-shaped acetabulum, where head of femur articulates. The two halves of the pelvic girdle meet ventrally to form pubic symphysis containing fibrous cartilage. It provides articulation to the bones of the leg, supports and protects abdominal viscera. It also provides attachment to certain leg muscles. Joints The place of articulation between two or more bones or between a bone and a cartilage is called a joint. The study of joints is known as arthrology. Classification of Joints There are three major structural forms, i.e., fibrous, cartilaginous and synovial. Fibrous (Immovable Joints) They do not allow movement because the bones are held firmly by bundles of dense white fibrous tissue. e.g., The sutures (joints between the bones of skull) and syndesmosis (joint between tibia and fibula). Cartilaginous (Slightly Movable Joints) They allow slight movement because of the elastic pads of fibrocartilage present between the ends of the bones taking part in the joints, e.g., Pubic symphysis of pubis, the joints between the adjacent vertebrae in the vertebral column. Synovial (Freely Movable Joints) A considerable movement is allowed at all synovial joints. They are surrounded by tubular articular capsule. The capsule consists of two layers, i.e., outer fibrous capsule and inner synovial membrane which secretes synovial fluid’ that lubricates and is responsible for providing nourishment to articular cartilage. In old age, stiffness of joints is due to decrease in synovial fluid. According to shape of bones and types of movement, the synovial joints are of following six types (i) Ball and Socket Joint In this type, a ball-like structure on one bone fits into a socket like structure in another bone, e.g., Shoulder joint (between pectoral girdle and head of humerus) and hip joint (between acetabulum and head of femur). (ii) Hinge (Knee) Joint This joint allows the movement in one plane only, e.g., Elbow, knee, ankle and interphalangeal joints. (iii) Pivot Joint This joint is responsible for providing movement in one plane, e.g., Joint between atlas and axis and radioulnal joint (between radius and ulna). (iv) Gliding Joint This joint allows limited movement in all direction as the bones are closely packed together or held in place by ligaments, e.g., Joints between the carpal bones and between the tarsal bones. (v) Saddle Joint This type of joint is like ball and socket joint but not developed fully, e.g., Joint between carpal of hand and metacarpal of thumb. (vi) Condyloid or Ellipsoid Joint This allows movement in two planes (i.e., back-forth and side-side), e.g., joint between metacarpals and phalanges (metacarpophalangeal joint) of the fingers. Some Common Injuries of the Joints Partially or completely torn ligament. Dislocation Occurs when bones are forced out of a joint, often accompanied by sprains, inflammation and joint immobilisation. Cartilage tears Cartilage may tear when joints are twisted or when pressure is applied to them. Functions of Joints Joints serves following functions in human body (i) These are essential for all types of movement. (ii) Force generated by muscles is used to carry out movement through joints, where joints acts as a fulcrum. (iii) The joints make body flexible. (iv) Some joints allow the growth of the structures that they connect to. Disorders of Muscular and Skeletal System Myasthenia Gravis It is a chronic, autoimmune, neuromuscular disease characterised by varying degrees of weakness in the skeletal muscles of body. It leads to fatigue and ultimately to paralysis of skeletal muscles. Muscular Dystrophy It is an inborn (genetic) disorder of muscles associated * with dysfunction and ultimately with deterioration. The patient is unable to walk after the age of 12, death usually by the age of 20. Tetany It is an abnormal condition characterised by periodic painful muscular spasms (wild contractions) and tremors. It is caused by low calcium levels in body fluid and associated with diminished function of parathyroid gland. Arthritis It is caused by inflammation of the joints. It is of several types, some of them are as follows (a) Rheumatoid Arthritis It is an inflammation of the synovial membrane in synovial joints, may seem to occur at any age. (b) Osteoarthritis/Degenerative Joint Disease It is characterised by progressive erosion of articular cartilage at synovial joint. (c) Infectious Arthritis It is a form of joint inflammation caused by a microorganism (such as bacterium, virus or a-fungus). (d) Gout/Gouty Arthritis It is the type of arthritis that occurs mainly due to defect or accumulation of uric acid crystals. NOTE: * Still’s disease (Juvenile rheumatoid arthritis) is another kind of rheumatoid arthritis that occurs in younger people * There is no cure for this type of arthritis. However, pain releiving (analgesic) drugs are available to give comfort. b. Osteoporosis In this, a reduction in bone tissue mass occurs, causing weakness of skeletal strength. It results from excessive resorption of calcium and phosphorus from the bone, decreased level of oestrogen is a common cause for this (a) It is an age-related disorder that is more common in women than in men. (b) It leads to increased chances of fractures.

CLASS 11 CHAPTER 19: EXCRETORY PRODUCTS AND THEIR ELIMINATION
https://acrobat.adobe.com/id/urn:aaid:sc:EU:14e15a5e-5894-44b0-adbf-8b2ab9f33d40 CLASS 11 CHAPTER 19: EXCRETORY PRODUCTS AND THEIR ELIMINATION Excretion is the removal of nitrogenous waste products and other metabolites from the animal body which is normally associated with the process of maintenance of osmotic concentrations, i.e., osmoregulation within the body. Both excretion and osmoregulation are important for the maintenance of homeostasis, i.e., for keeping the internal environment of the body constant that is necessary for normal life processes. Ammonia, urea and uric acid are the major forms of nitrogenous wastes excreted by animals. These substances get accumulated in the animal body either by metabolic activities or by other means like excess ingestion. Types of Nitrogenous Excretion Depending upon the nature of excretory product, animals exhibit different processes of nitrogenous excretion. These are described as follows (i) Ammonotelism: Ammonia is the most toxic form of nitrogenous waste, it requires large amount of water for its elimination. The organism that excrete ammonia are called ammonotelic and this , process to eliminate ammonia is known as ammonotelism. Examples of ammonotelic animals are Many bony fishes, aquatic amphibians and aquatic insects. Ammonia, as it is readily soluble, is generally excreted by diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions. Kidneys does not play any significant role in its removal. (ii) Ureotelism: The process of excreting urea is called ureotelism. Animals, which does not live in high abundance of ‘water convert ammonia produced in the body into urea (in the liver) and release into the blood, which is filtered and excreted out by the kidneys. Examples of ureotelic animals are Mammals, many terrestrial amphibians and marine fishes. (iii) Uricotelism: The process of excreting uric acid is called uricotelism. Uric acid, being the least toxic nitrogenous waste can be removed with a minimum loss of water from the animal body. Thus, it is excreted in the form of pellet or paste (i.e., semi-solid form). Normally, the animals which live in desert exhibit uricotelism. Examples of uricotelic animals are Reptiles, birds, land snails and insects. Note: Some animals perform dual excretion, i.e., two modes of excretion. For example, Earthworms excrete ammonia when sufficient water is available, while it excretes urea in drier surroundings. Other examples are lung fishes, Xenopus, crocodiles, etc. Excretory Organs Different animal groups have a variety of excretory structures (organs) to perform the process of excretion. In most of the invertebrates, these structures are simple tubular form, whereas, vertebrates have complex tubular organs called kidneys. Some of these structures are mentioned below in the given table Excretory Organs and Main Nitrogenous Wastes of Different Animal Groups Human Excretory System Human excretory system consists of a pair of kidneys, a pair of ureters, urinary bladder and urethra, these are described below in detail 1. Kidneys These are reddish brown, bean-shaped structures situated between the levels of last thoracic and third lumbar vertebra close to the dorsal inner wall of the abdominal cavity. – Kidneys are mesodermal in origin. Position of Kidneys The kidneys are located below the diaphragm on the left and right sides. The right kidney is lower and smaller than the left kidney because the liver takes up much space of the right side. Note: Each kidney of an adult human measures. 10-12 cm in length, 5-7 cm in width, 2-3 cm in thickness with an average weight of 120-170 gm (i.e., 150 gm in males and about 135 gm in females). Structure of Kidney Structure of kidney can be studied well under two heads, i.e., external as well as internal structure. These are described below as The outer surface of each kidney is convex and inner surface is concave, where it has a notch called hilum, through, which the supply of blood occurs, i.e., renal artery and renal vein, pass in and out of the kidneys along with the ureter and the nerve supply of kidney. If we look from outside to inside, three layers cover the kidneys, i.e., renal fascia (outermost), the adipose layer and then renal capsule (innermost layer). These coverings protect the kidneys from external shocks and injuries. The LS of a mammalian kidney seems to have of an outer cortex and inner medulla. Inside the kidney, the ureter is expanded as a funnel-shaped cavity called pelvis. The free end of pelvis has number of cup-like cavities called calyces (sing, calyx) major and minor. Medulla projects into the calyces as conical processes, called renal pyramids or medullary pyramids. The tip of pyramids are called renal papillae. The cortex spreads in between medullary pyramids as renal columns called columns of Bertini. Microscopic Structure Each kidney is composed of numerous (nearly one million) complex tubular structure called nephrons, which are the functional units of kidney. Structure of Nephron Uriniferous Tubule Each nephron consists of two parts, i.e., the Malpighian body or renal corpuscle and the renal tubule. i. Malpighian Body or Renal Corpuscle Glomerulus along with Bowman’s capsule is called the Malpighian body or renal corpuscle which filters out large solutes from the blood and delivers small solutes to the renal tubule for modification. * Glomerulus It is a tuft of capillaries formed by the afferent arteriole (a fine branch of renal artery). The afferent arteriole is short and wide that supplies blood to the glomerulus, while, the efferent arteriole is narrow and long carrying blood away from the glomerulus. Differences between Afferent Arteriole and Efferent Arteriole ii. Bowman’s Capsule (Glomerular capsule) It is a double walled cup-like structure that surrounds the glomerulus. The outer parietal wall which is composed of flattened (squamous) cells and the inner visceral wall is composed of a special type of less flattened cells, called podocytes. iii. Renal Tubules Just below the glomerulus, the tubule has a very short neck. Attached to each Bowman’s capsule is a long, thin tubule with three distinct regions. These regions are described as follows (a) Proximal Convoluted Tubule (PCT) Behind the neck, it makes few coils and is restricted to the cortical region of the kidney. (b) Henle’s Loop It is quite narrower and U-shaped (or hair pin-shaped) having a descending limb that ends into the medulla and an ascending limb that extends back from the medulla into the cortex. Differences between Descending Limb and Ascending Limb of Henle’s Loop Types of Nephrons Based on the location in the kidney, nephrons are of following two types 1. Cortical Nephrons In majority of nephrons, the loop of Henle is too short and extends only very little into the medulla i.e., lie in the renal cortex. Such two nephrons are called cortical nephrons. Juxtamedullary Nephrons In some of the nephrons, the loop of Henle is very long and runs deep into the medulla. These nephrons are called juxtamedullary nephrons. The cortical nephron forms about 80% of the total nephron count while rest 20% are the juxtamedullary nephron. Functions of Kidney Following functions are served by kidney (i) Regulation of water and electrolyte balance. (ii) Regulation of arterial pressure. (iii) Excretion of metabolic waste and foreign chemicals. (iv) Secretion of hormones like renin. 2. Ureters The pelvis of each kidney is continued as a ureter and emerges out at hilus. Ureter is a long and muscular tube. Ureters of both sides extend posteriorly and open into the urinary bladder. 3. Urinary Bladder It is a thin-walled, pear-shaped, white transparent sac present in the pelvic cavity. It temporarily stores the urine. 4. Urethra It is a membranous tube, which conduct urine to the exterior. The urethral sphincters keep the urethra closed except during voiding of urine. The formation of urine is the result of the following processes 1. Glomerular Filtration The first step of urine formation is the filtration of blood, which is carried out by the glomerulus. That’s why this step is called glomerular filtration. Kidneys filter about 1100-1200 mL of blood per minute, which constitute roughly l/5th of the blood pumped out by each ventricle of the heart in a minute. The glomerular capillary bloodpressure causes filtration of blood through three layers, i.e., (i) the endothelium of glomerular blood vessels. (ii) the epithelium of Bowmans capsule. (iii) a basement membrane (present between the above mentioned two layers). The podocytes (epithelial cells of Bowman’s capsule) are arranged in such a manner so, as to leave some minute spaces called filtration slits or slit pores. On account of the high pressure in the glomerular capillaries, the substances are filtered through these pores into the lumen of the Bowman’s capsule (but the RBC, WBC and plasma proteins having high molecular weight are unable to pass out). That’s why this process of filtration through glomerular capillaries in the Bowman’s capsule is known as ultra filtration and the filtrate is called glomerular filtrate or primary urine. It is hypotonic to urine that is actually excreted. Basic function of nephron is to clear out the plasma from unwanted substrates and also maintain the osmotic concentration of the blood plasma. Thus, the fluid coming out is known as urine, whose formation occurs inside the kidney. Glomerular Filtration Rate: The amount of the filtrate formed by the kidneys per minute is called Glomerular Filtration Rate (GFR). In a healthy person it was found approximately 125 mL/min, i.e., 180 L/day. GFR is regulated by one of the efficient mechanism carried out by Juxtaglomerular Apparatus (JGA). JGA is a special sensitive region formed by cellular modifications in the distal convoluted tubule and the afferent arteriole at the location of their contact. A fall in GFR can activate the JG cells to release renin, which can stimulate the glomerular blood flow and thereby, the GFR back to I normal. 2. Selective Reabsorption This is the second step in the formation of urine from filtrate. The urine released is 1.5 L as compared to the volume of the filtrate formed per day (180 L). It suggests that as much as 99% of the material in the filtrate is reabsorbed by the renal tubules. Thus, the process is called reabsorption. Depending upon the types of molecules being reabsorbed, movements into and out of epithelial cells in different segments of nephron occur either by passive transport or active transport. These are described as follows (i) Water and urea, are reabsorbed by passive transport (i.e., water is reabsorbed by osmosis and urea by simple diffusion). (ii) Glucose and amino acids are reabsorbed by active transport. (iii) The reabsorption of Na+, occurs both by passive and active transport. 3. Tubular Secretion It is also an important step in urine formation. Certain chemicals in the blood that are not removed by filtration from the glomerular capillaries are removed by this process of tubular secretion. It helps in the maintenance of ionic and acid-base balance of body fluids by removing chemicals like foreign bodies, ions (K+, H+, NH–) and molecules (medicines), etc., that are toxic at elevated levels. Difference between the Tubular Re-absorption and Tubular Secretion Functions of the Tubules When the glomerular filtrate/primary urine passes through renal tubule, water and different materials of filtrate reabsorb at various places. These are given below in the following manner i. Proximal Convoluted Tubule (PCT) The epithelial cells of the PCT have numerous microvilli (simple cuboidal brush-border epithelium) which increase the surface area available for reabsorption. The process of reabsorption mostly (65%) takes place within PCT (i.e., nearly all of the essential nutrients, 70-80% of electrolytes and water). PCT also helps in the absorption of HCO– from the filtrate. Selective secretion of hydrogen ions, ammonia and potassium ions takes place here to maintain the pH and ionic balance of the body fluids. The filtrate is considered isotonic to blood plasma. ii. Henle’s Loop Reabsorption in Henle’s loop is minimum, besides it, this plays an important role in maintaining the high osmolarity of medullary interstitial fluid. Two portions of Henle’s loop, play different role in osmoregulation such as a. Descending Limb of Loop of Menu? Water is reabsorbed here due to increasing osmolarity of interstitial fluid but, sodium and other electrolytes are not reabsorbed here. This concentrates the filtrate as it moves down. b. Ascending Limb of Loop of Menu? This segment is impermeable to water but permeable to K+,Cl– and Na+ and partially permeable to urea. Thus, in the thick ascending limb of the loop of Henle Na+, K+, Mg2+ and Cl– are reabsorbed. Therefore, as the concentrated filtrate pass upward, it gets diluted due to the passage of electrolytes to the medullary fluid. iii. Distal Convoluted Tubule (DCT) Active reabsorption of sodium ions from the filtrate (under the influence of aldosterone) takes place. Water is also reabsorbed here under the influence of Antidiuretic Hormone (ADH). With associated secretion of potassium (K+), hydrogen (H+) ions, NH–, some Cl– (chloride) ions and HCO– are also reabsorbed here. It is necessary to maintain the pH and sodium-potassium balance in blood. This makes the filtrate isotonic to blood plasma. Collecting Duct This duct extends from the cortex of the kidney to the inner parts of the medulla and is highly permeable to water. Thus, a considerable amount of water is reabsorbed here under the influence of ADH to produce concentrated filtrate. Sodium is also reabsorbed here under the influence of aldosterone. CT (Collecting Tubule) allows passage of small amounts of urea into the medullary interstitium to maintain the osmolarity. It also plays an important role in the maintenance of pH and ionic balance of blood by the selective secretion of H+ and K+ ions. Therefore, the filtrate is now called urine. Thus, urine is isotonic to medullary fluid and hypertonic to blood. Concentrations of important ions and other substances in the blood are controlled by regulating water levels. Counter Current Mechanism Kidney of higher vertebrates (such as mammals, birds including man) has the ability of absorbing more and more water from tubular filtrate (in the Henle’s loop region) to make the urine more concentrated. This can be achieved by a special mechanism known as counter current mechanism and also known as urine concentration mechanism. Basic Concept (i) Henles loop and vasa recta (capillary loop) play an important role in this mechanism. The flow of filtrate in the limbs of Henle’s loop is in opposite directions and thus, forms a counter current. The flow of blood with in the two limbs of vasa recta also occur in the counter current pattern. (ii) The osmolarity (i.e., number of Osmols of solute per litre) of renal cortical interstitium is the same (300 m Osmol/ L) as in other tissues, but that of the interstitium of renal medulla is hypertonic with a gradient of hyperosmolarity from renal cortex to the tips of medullary papillae. The hyperosmolarity of medullary interstitium near the tips of the papillae is as high as 1200-1450 m Osmol/L. The Mechanism The gradient of increasing hyperosmolarity of medullary interstitium is maintained by a counter current mechanism and the proximity between the Henle’s loop and vasa recta. This gradient is mainly caused by NaCl and urea. The transport of these substances is facilitated by the special arrangement of Henle’s loop and vasa recta. There are two aspect of this mechanism (i) Counter current multiplication (by the Henle’s loop). (ii) Counter current exchange (by the vasa recta). NaCl is transported by the ascending limb of Henle’s loop, which is exchanged with the descending limb of vasa recta. NaCl is returned to the medullary interstitium by the ascending part of vasa recta. But, contrarily, the water diffuses into the blood of ascending limb of vasa recta and is carried away into the general.blood circulation. Permeability to urea is found only in the deeper parts of thin ascending limb of Henle’s loops and collecting ducts.Urea diffuses out of the collecting ducts and enters into the thin ascending limb. A certain amount of urea recycled in this way is trapped in medullary interstitium by the collecting tubule. Thus, collecting tubule also play a minor role in the process (as shown in the figure above). Regulation of Kidney Functions To maintain homeostasis, the regulation of water and solute contents of the body fluids is performed by the kidneys. The vertebrate kidney is very flexible in its functioning. It excretes larger quantities of dilute urine when water is abundant in the body tissues and small amounts of concentrated urine when there is shortage of water. Hormones acts as an important signaling molecules in controlling the regulatory processes in the kidneys. The functioning of the kidneys is efficiency monitored and regulated by hormonal feedback mechanisms involving hypothalamus, JGA (Juxtaglomerular Apparatus) and to a certain extent, the heart. Regulation of the functioning of kidneys can be discussed under the following headings Regulation by the Hypothalamus Excessive loss of fluid from the body activates osmoreceptors, which stimulate the hypothalamus to release ADH or vasopressin form the neurohypophysis. ADH facilitates water reabsorption from posterior parts of tubule. An increase in body fluid volume can switch off the osmoreceptors and suppresses the ADH release to complete the feed back. ADH also causes constrictory effects on blood vessels. This causes an increase in blood pressure, which in turn increase the glomerular blood flow and thereby the GFR (Glomerular Filtration Rate). Regulation by the Juxtaglomerular Apparatus (JGA) As blood pressure/glomerular blood flow /GFR decreases, the cells of the JGA release the enzyme renin. Renin converts angiotensinogen in blood to Angiotensin I and Angiotensin II (active form). This mechanism is generally known as the Renin-angiotensin mechanism. Angiotensin has following effects (a) Raises blood pressure by constricting blood vessels (being a powerful vasaconstrictor) and thereby, GFR. (b) Activates the adrenal cortex to release aldosterone. (c) Aldosterone causes reabsorption of Na+ and water from the distal parts of the tubule. This also leads to an increase in blood pressure and GFR. Regulation by the Heart Atrial Natriuretic Factor (ANF) produced by the atria of heart can cause vasodilation (dilation of blood vessels) and thereby, decrease the blood pressure. ANF inhibits NaCl reabsorption and concentration of urine. Micturition Urine is produced and drained continuously by the nephron into the renal pelvis from here, it is carried down to the ureters and then into the urinary bladder. The bladder serves to store the urine temporarily till a voluntary signal is given by the Central Nervous System (CNS). As urine collects, the muscular walls of the bladder distend to accommodate it. . The stretch receptors on the walls of the bladder set up reflexes (send signals to the (CNS) by stimulating the sensory nerve ending in the bladder). It causes an urge to pass out urine. The act of expulsion of urine involves the coordinated contraction (as CNS passes on motor messages) of the smooth muscle of the bladder wall and simultaneous relaxation of the internal and external urethral sphincters. The process of release of urine is called micturition and the neural mechanism causing it is called the micturition reflex. Urine An adult man normally passes about 1-1.5 L of urine per day. Composition Urine normally contains, water 95%, salts 2%, urea 2.6%, uric acid 0.3%, traces of creatinine, creatine, ammonia, etc. Colour Pale yellow, due to pigment urochrome produced by the breakdown of haemoglobin. pH Ranges from 4.5-8.2, average pH 6.0 (i.e., slightly acidic). Odour Unpleasant, if allowed to stand imparts strong smell like, ammonia. Role of Other Organs in Excretion Other than the kidneys, there are some accessory excretory organs also that help in the elimination of excretory wastes. These are described as follows 1. Lungs Carbon dioxide and water are the waste products formed in respiration. Lungs remove the CO2 and some water as vapour in the expired air. About 18 L of CO2 per hour and 400 mL of water per day are eliminated by human lungs. 2. Liver It changes the decomposed haemoglobin of the worn-out red blood corpuscles into bile pigments, i.e., bilirubin and biliverdin. These pigments passes into the alimentary canal with the bile for elimination in the faeces. The liver also excretes cholesterol, steroid hormones, certain vitamins and drugs via bile. Liver deaminates the excess and unwanted amino acids, producing ammonia, which is quickly combined with CO2 to form urea in urea cycle or Ornithine cycle, which is further removed by the kidneys. 3. Skin The sweat and sebaceous glands in the skin can eliminate certain substances through their secretions. (i) Sweat Glands The secretion of sweat glands (sweat) is an aqueous fluid containing NaCl, lactic acid, small amounts of urea, amino acids and glucose. Control of sweat lost is an example of homeostasis control, for regulating the body temperature (i.e., to facilitate a cooling effect on the body surface). (ii) Sebaceous Glands Sebum from sebaceous glands eliminates sterols, fatty acids, waxes and hydrocarbons. This secretion is mainly meant for protective oily covering of the skin. 4. Intestine Epithelial cells of colon excrete excess salts of calcium, magnesium and iron along with faeces. 5. Salivary Glands Heavy metals and drugs are excreted in the saliva. Important Metabolic Wastes and Substances Excreted from the Body Disorders of the Excretory System Malfunctioning of kidneys can lead to several disorders of the excretory system. Some of these are as follows (i) Uremia It is the presence of an excessive amount of urea in the blood. Urea is highly harmful as it poisons the cells at high concentration and may lead to kidney failure. (ii) Kidney Failure (renal failure) Partial or total inability of kidneys to carry on excretory and salt-water regulatory functions is called renal or kidney failure. (iii) Renal Calculi It is the formation of stone or insoluble mass of crystallised salts (calcium, magnesium, phosphates and oxalates etc.), formed within the kidney. (iv) Glomerulonephritis It is the inflammation of glomeruli of kidney. Artificial kidney (haemodialyser) is a machine that is used to filter the blood (to remove urea and other nitrogenous wastes) of a person, whose kidneys are damaged. The process is called haemodialysis. The outline details of apparatus and the process are as follow (i) It works on the principle of dialysis (i.e., diffusion of small solute molecules through a semipermeable membrane (cellophane). (ii) Blood of the patient is pumped from one of the arteries into the dialysing unit (haemodialyser) after cooling it to 0°C and mixing with an anticoagulant (heparin). (iii) Haemodialyser is a cellophane tube suspended in a dialysing fluid (salt-water solution) of the same composition as that of plasma except the nitrogenous wastes (urea). (iv) Pores of the cellophane tube allow the passage of molecules based on concentration gradient. Nitrogenous wastes like urea, uric acid, creatinine,excess salts and excess H+ ions easily get diffuse from the blood into the surrounding solution. Thus, the blood is cleared of nitrogenous waste products without loosing plasma proteins. (v) The blood thus, purified, is warmed to body temperature, checked to ensure that it is isotopic to the patients blood. Now, the blood is mixed with an anti-heparin to restore its normal clotting power and then pumped back to the body of patient through a vein, usually the radial vein. Kidney (Rena!) Transplantation Grafting a kidney from a compatible donor to restore kidney functions in a recipient suffering from kidney failure is called renal or kidney transplantation. It is an ultimate method in the correction of acute renal failures. A living donor can be used in a kidney transplant. It may be an identical twin, a sibling or a close relative to minimize the chances of rejection by the immune system of the host. To prevent the rejection of transplanted kidney, special drugs are also used, which suppress the recipients immune system.

Class 11 Biology Chapter 19 Chemical Coordination and Integration
https://acrobat.adobe.com/id/urn:aaid:sc:EU:bd9d61c2-977a-4aea-a895-c680b4b9e96b Class 11 Biology Chapter 19 Chemical Coordination and Integration The nervous system in the body, provides point-to-point coordination among the organs. The neural coordination is rapid, but short lived in nature. However, the nerve cells of not reach to each and every cell of the body. So, a special kind of coordination and integration is provided to each cell for continuous cellular functions. This special function is performed by hormones. Thus, the nervous system and endocrine system are intimately related to each other forming neuroendocrine system together that jointly coordinate together that regulate the physiological functions of the body. Endocrinology : Major Glands and Their Hormones Endocrine Glands and Hormones The endocrine glands are ductless glands, i.e., lack ducts. They pour their secretion into the surrounding blood for transport to the site of action or distandy located target organ. Their secretions are called hormones or internal secretion. The glands, which have ducts for discharging their secretions onto the body surfaces or into the cavities in the body are called exocrine glands, e.g., Liver, salivary glands, etc. Hormones These are non-nutrient chemicals, which are produced in trace amounts and acts as intercellular messengers. These are responsible for regulating the biological processes in the body. The organized endocrine glands also secretes a number of new molecules in addition to the hormones. Vertebrates have large number of chemicals acting as hormones that provide coordination, while invertebrates possess very simple endocrine systems with few hormones. Types of Human Endocrine Glands The endocrine glands are of following two types in humans i. Pure Endocrine Glands It entirely work for the secretion of hormones. They include the hypothalamus, pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus glands and gonads (i.e., testes in males and ovaries in females). ii. Partial Endocrine Glands These are partly endocrine and partly exocrine in function. They includes kidneys, liver, gastro-intestinal tract, heart, placenta, etc. Structure and Functions of Major Endocrine Glands Hypothalamus In humans, the complete endocrine system works more or less under the influence of hypothalamus. Location Hypothalamus is located in the basal part of diencephalon (forebrain) regulates a wide spectrum of functions in the body. Origin It develops from the ectoderm of embryo like other parts of brain. with the anterior lobe of pituitary by hypophysial portal blood vessels and to the posterior lobe of pituitary by the axons of its neurons. Hormones Hypothalamus contains several groups of neuro-secretory cells, known as nuclei, which produce hormones. The function of these hormones is to regulate the synthesis and secretion of pituitary hormones. Hormones produced by hypothalamus are of following two types i. Releasing Hormones These are the hormones that stimulates, the secretion of pituitary hormones, e.g., Gonadotrophin Releasing Hormone (GnRH) which stimulates the gonadotroph cells of anterior pituitary gland to release gonadotrophins. ii. inhibiting Hormone These are the hormones that inhibits the release of pituitary hormones, e.g., Somatostatin, which inhibits the secretion of growth hormone from anterior lobe of pituitary gland. All these hormones originating in the hypothalamic neurons, passes through the axons and are released from their nerve endings. These hormones finally reach the pituitary gland through a portal circulatory system (hypophyseal portal system) thereby, regulating the functions of anterior pituitary. The posterior pituitary however, functions under the direct regulation of the hypothalamus. Pituitary Gland (Hypophysis) It is the smallest endocrine gland, but serve very important role in the human endocrine system. It directly or indirectly controls almost all other endocrine glands of the body. It is also known as master gland. Origin It originates from the ectoderm of the embryo. Location and Structure It is reddish grey in colour and is roughly oval in shape. It is about a size of a pea seed. The pituitary gland is located in a small bony cavity of the brain called sella tursica. Anatomy The pituitary gland has three major lobes, i.e., anterior, intermediate and posterior lobe. It is anatomically divided into two major portions i. Adenohypophysis It is the glandular anterior portion of the pituitary gland. It further consists of two parts, i.e., pars distalis and pars intermedia.These two parts represent the anterior and intermediate lobes of pituitary. a. Pars Distalis It also called anterior pituitary. It produces different hormones. These hormones given below with their functions * Growth Hormone (GH), stimulates the somatotroph cells of anterior lobe of pituitary gland to release its Growth Hormone or somatotrophin. It stimulates body growth, protein, fat and carbohydrate metabolism. Over secretion of this hormone during childhood causes gigantism (excessive growth of bones), whereas in adulthood causes acromegaly (abnormal thickness of bones). Its low secretion results in stunted growth, i.e., pituitary dwarfism. * Prolactin (PRL) The prolactin releasing hormone stimulates lactotroph cells of the anterior lobe of pituitary gland to secrete its prolactin. PRL regulates the growth of mammary glands and formation of milk in them. * Thyroid Stimulating Hormone (TSH) Thyroid releasing hormone stimulates thyrotroph cells of the anterior lobe of pituitary to secrete its thyroid stimulating hormone, i.e., TSH or thyrotrophin. This TSH stimulate the synthesis and secretion of thyroid hormones from the thyroid gland. * Adrenocorticotrophic Hormone (ACTH) This is secreted when adrenocorticotrophin releasing hormone (ACRH) stimulates the corticotroph cells of anterior lobe of pituitary. This stimulates the synthesis and secretion of steroid hormones called glucocorticoids from the adrenal cortex. * Gonadotrophin Hormone It is the gonadotroph cells of anterior lobe of the pituitary gland, which secrete, leuteinizing hormone (LH) and follicle stimulating hormone (FSH). Both of these hormones stimulates the gonadal activity hence, called gonadotrophin. * Leuteinising Hormone (LH) In males, it stimulates the synthesis and secretion of hormones called androgens from testis. While, in females, it induces ovulation of fully mature follicles (Graafian follicles) and also helps in maintaining the corpus luteum formed from the remnants of the Graafian follicles after ovulation. * Follicle Stimulating Hormone (FSH) In males, the FSH and androgens together regulate spermatogenesis. In females, this hormone stimulates the growth and development of ovarian follicles. Details of both hormones (i.e, FSH and LH) and the regulation of different hormones will be studied in class XII. b. Pars Intermedia or Intermediate Lobe This portion of adenohypophysis secretes only one hormone, * Melanocyte Stimulating Hormone (MSH) The melanocyte releasing hormone stimulates the intermediate lobe of pituitary gland to secrete its melanocyte stimulating hormone. MSH acts on melanocytes (melanin containing cells) and regulates the pigmentation of the skin. Like MSH, another hormone called Melanocyte Inhibiting Hormone (MIH) is also secreted, which inhibits the secretion melanocyte stimulating hormone. ii. Neurohypophysis It is a collection of axonal projections from the hypothalamus, which terminates behind the anterior pituitary gland. It is pars nervosa of the neurohypophysis that forms the posterior lobe of pituitary gland. The posterior pituitary stores and releases two hormones given below a. Oxytocin It is a short peptide of nine amino acids, also known as pitocin. It acts on the smooth muscles of our body and stimulates a vigorous contraction of uterus at the time of child birth. It also plays role in ejection of milk from the mammary glands in females. b. Vasopressin It is a small peptide hormone, also known as antidiuretic hormone (ADH) or pitressin. This hormone acts mainly at the kidney, stimulating the re-absorption of water and electrolysis by the distal tubules. Thereby reducing the loss of water through urine (diuresis). Hormones It secrete a hormone called melatonin that plays a very important role in the regulation of a 24 hrs (diurnal) rhythm of our body and Melatonin also helps in maintaining the normal rhythms of sleep-wake cycle, body temperature. Metabolism, pigmentation, menstrual cycle as well as our defence capability is also influenced by this hormone. The melatonin hormone promotes sleep, so it is also known as sleep hormone. Thyroid Gland The thyroid gland is known to be the largest endocrine gland. Origin It is endodermal in origin, i.e., originates from the endoderm of the embryo. The thyroid gland is bilobed, highly vascular organ. Location and Structure It surrounds the front of the larynx and is composed of two lobes. Each of its lobe is located on either side of the trachea in the neck interconnected with each other through a thin flap of connective tissue called isthmus. It is composed of follicles (round in shape) held together by loose connective tissue called stromal tissues. Each thyroid follicle is composed of follicular cells, enclosing a cavity. Hormones The follicular cells synthesise following two hormones (i) Tetraiodothyronine or thyroxine (T4) hormone (ii) Triiodothyronine (T3) hormone. Both these hormones are iodmated forms of the amino acid (tyrosine). They are stored in the colloid that fills the follicles and are released to the blood when needed. Iodine (in diet) is essential for the synthesis of hormone at normal rate in thyroid. Disorders i. Hypothyroidism This disorder occurs due to the deficiency of iodine in our diet. It leads to the enlargement of thyroid gland commonly known as goitre. (а) Hypothyroidism in women at the time of pregnancy affects the development and maturation of the growing baby and leads to stunted growth (cretinism), mental retardation, low intelligence quotient, abnormal skin, deaf-mutism, etc. (b) Hypothyroidism in adult women may cause irregular menstrual cycle. ii. Hyperthyroidism It is the condition during which, rate of synthesis and secretion of thyroid hormones is increased to abnormal high levels. It may occur due to the cancer of the thyroid gland or due to development of nodules of the thyroid gland. It adversely affects the body physiology of an organism. Functions of Thyroid Hormones Thyroid hormone serves several function in the body, such as (i) These hormones regulates and maintains the basal metabolic rate (BMR), i.e., both T3 and T4 hormones increases the overall metabolic rate of the body. (ii) They support the process of formation of red blood cells. Also helps in controlling the metabolism of carbohydrates, proteins and fats. (iii) Influences the maintenance of water and electrolyte in our body. Apart from the hormone T3 and T4, thyroid gland also secretes a protein hormone called thyrocalcitonin (TCT). Its main function is to regulate the level of calcium in blood. Parathyroid Gland These are small glands in the human neck that produces parathyroid hormone. Origin It is endodermal in origin. Location These glands are situated on the posterior side of the thyroid gland. Structure Parathyroid glands are four in number, i.e., each pair is situated in the two lobes of the thyroid gland on either side. These are small, flat and oval gland. Parathyroid glands secretes a single hormone known as parathormone or parathyroid hormone (PTH) (functions opposite to the thyrocalcitonin hormone). The secretion of PTH is regulated by the circulating level of calcium ions in the blood. Functions of Parathyroid Hormone Parathyroid hormone serve several functions in the body, such as (i) It increases the level of Ca2+ levels in the blood. (ii) It stimulates the process of bone re-absorption (i.e., dissolution/demineralisation) by acting on bones. (iii) It also stimulates re-absorption of Ca2+ by the renal tubules and absorption of Ca2+ from the digested food. By the above mentioned functions of parathyroid hormone, it is clear that PTH acts as a hypercalcaemic hormone (increases the level of Ca2+ in the blood). Parathyroids are under the feedback control of blood calcium level. A fall in Ca2+ in blood stimulates them to secrete PTH. Thus, both the hormones (TCT and PTH) play a significant role to control and regulate the concentration of Ca2+ and phosphorus. Thymus It is a lymphoid gland that play an important role in the development of immune system. Origin It arises from the endoderm of the embryo. Structure and Location The thymus gland is a lobular structure situated on the dorsal side of the heart and the aorta (in the upper part of thorax near the heart). It is a soft, pinkish, bilobed mass of lymphoid tissue and is a prominent gland that gets degenerated with age. Hormones The thymus gland secretes peptide hormone called thymosin, which plays a major role in the differentiation of T-lymphocytes, which provides cell-mediated immunity. Thymosins, when released in the blood has a stimulating effect on the entire immune system. Apart from this thymosin also promotes production of antibodies to provide humoral immunity. Its degeneration with age occurs due to which production of ‘ thymosin hormone also gets decreased. Thus, resulting in weaker immune response in old people. Adrenal Gland (Suprarenals) Location Our body has a pair of adrenal glands. Each located at the anterior part of each kidney. Structure Adrenal glands are conical yellowish bodies composed of two types of tissues. These are as follows 1. Adrenal Cortex It is an external firm, pale yellowish tissue derived from mesoderm of embryo. It is further divided into three concentric layers (a) Zona Reticularis It is the inner layer of the cortex whose cells are arranged in the net like fashion. (b) Zona Fasciculata It is the middle layer of the cortex. It is the widest of all three layers. (c) Zona Glomerulosa It is the outermost layer. It is composed of five layers compactly arranged cells. Hormones secreted by these three layers of adrenal cortex are collectively known as corticoids. Three groups of steroid hormones are secreted by adrenal cortex, such as i. Mineralocorticoids (Aldosterone) They regulate the balance of water and electrolytes in our body. Aldosterone is the major mineralocorticoid found in our body. It mainly acts on renal tubules stimulating the re-absorption of Na+ and water. Also stimulate the excretion of K+ and phosphate ions from the body. Its main function is in maintaining electrolytes, body fluid volume, osmotic pressure and blood pressure of the body. ii. Glucocorticoids (Cortisol) These are the hormones, which regulate the metabolism of carbohydrates, proteins and fats. Cortisol is the main glucocorticoid found in our body. (a) Cortisol stimulates the liver for the synthesis of carbohydrates from non-carbohydrate sources (like amino acids and glycerol). This process is known as gluconeogenesis. Hence, glucocorticoids stimulates gluconeogenesis, lipolysis and proteolysis. (b) Inhibition of cellular uptake and utilization of amino acids. (c) Cortisol is involved in the maintenance of cardiovascular system and in proper functioning of kidney. (d) Cortisol produces anti-inflammatory reactions and also functions in suppression of immune response. (e) It stimulates the production of RBC. iii. Sexocorticoids (Androgen) Adrenal cortex also produces a small quantity of androgenic steroids, i.e., sex hormone (androgens) both in males and females. These hormones are secreted as DHEA (Dehydroxy epiandrosterone), which acts as a precursor of both testosterone and estrogens. (a) It play a major role in the growth of axial, pubic and facial hair during puberty. (b) Development of acne are also due to these hormones in young girl. (c) It also plays an important role in the development of embryo (foetus). 2. Adrenal Medulla The adrenal medulla lies in the centre of the adrenal gland. It is an internal soft, dark reddish brown tissue derived from the ectoderm. The adrenal medulla secretes two hormones (i) Adrenaline (epinephrine) (ii) Nor-adrenaline (nor-epinephrine) Activation of Adrenaline -no Nor-adrenaline Both hormones belong to the category of compounds known as catecholamines and are secreted in response to any kind of stress danger and during emergency situations like fall in blood pressure or sugar level in creased respiratory rate, heart beat, etc. The CNS at the time of stress or danger stimulates the adrenal medulla to release both these hormones. These are also known as emergency hormones or hormones of fight or flight. These hormones serves following purposes (a) Increases, alertness. (b) Dilation of pupil. (c) Piloerection (raising of hairs of hands and legs). (d) Increase in heart beat and rate of respiration. (e) They also stimulate the breakdown of glycogen due to which the concentration of glucose increases in the blood. (f) Stimulate breakdown of lipids and proteins. Pancreas It is a composite gland that acts as both exocrine and endocrine gland. Origin It originates from the endoderm of the embryo. Location It lies below the stomach, in the loop of duodenum. Structure It is elongated yellowish gland that consists of large number of ducts. Besides these, pancreas consists of 1-2 millions of small group of specialized cells, called Islets of Langerhans (after the name of their discoverer Paul Langerhans in 1869). In normal human pancreas, these cells represents only 1-2% of the pancreatic tissue. Each islet consists of major two types of cells as (i) α-cells (about 25%) It secretes a peptide hormone called glucagon. (ii) β-cells (about 60%) It secretes a another peptide hormone called insulin. Hormones Glucagon and insulin hive antagonistic effect on blood glucose level. This can be clearedfrom the functioning given below i. Glucagon This peptide hormone plays an important role in maintaining the normal blood glucose levels. It brings about change of liver glycogen to blood glucose. Functions of Glucagon (a) It acts mainly on liver cells (hepatocytes) and stimulates glycogenolysis, which results in an increased blood sugar known as hyperglycaemia. (b) Apart from this glucagon also stimulates the process of gluconeogenesis which also contributes to hyperglycaemia. Glucagon is known as hyperglycaemic hormone because it reduces the cellular glucose uptake and utilization. (c) It reduces glycogenesis and also enhances lipolysis. Glucagon also stimulates the secretion of insulin from beta cells by its paracrine effect. ii. Insulin This peptide hormone plays a major role in regulation of glucose level in the blood. It mainly acts on hepatocytes and adipocytes (cells of adipose tissue), increasing the cellular glucose uptake and utilization. As a result, the movement of glucose takes place rapidly from blood to liver cells and cells of adipose tissues by decreasing the blood glucose level (hypoglycaemia). Insulin act as a powerful anabolic hormone. Deficiency Disorder of Insulin Diabetes mellitus is the common complex disorder caused due to prolonged hyperglycaemia. This is associated with the loss of glucose (when complete glucose cannot be reabsorbed by the kidneys) in the urine as pancreas fails to release adequate amount of insulin to. lower the level of glucose in the body. During this disorder, cells fails to utilize glucose and other carbohydrate for production of energy instead start utilizing proteins and fats for it (due to which person become weak). Diabetic patients are successfully treated with insulin therapy. (a) Insulin stimulates the conversion of glucose to glycogen (glycogenesis) in the target cells. (b) Decreases gluconeogenesis. (c) Decreases glycogenolysis. (d) Also reduces the catabolism of proteins and fats. (e) Increases synthesis of fat in the adipose tissue from fatty acids. Testis These are the primary sex organ of males. They perform dual role, i.e., function as endocrine gland apart from acting as male sex organ. Location A pair of testis is located in the scrotal sac (outside abdomen) of male individuals. Structure A testes is composed of many seminiferous tubules which are lined by germinal epithelium and stromal or interstitial tissue. This epithelium consists of three types of cells (i) Follicular cells give rise to sperms. (ii) Interstitial cells or Leydig cells secretes group of hormones called androgens mainly testosterone. (iii) Sertoli cells provides nourishment to sperms and also secretes hormone (inhibin). Hormone Interstitial cells present in the intertubular spaces produces a group of hormones, i.e., androgens. These include testosterone, dihydrotestosterone and androstenedione.But mainly secretes testosterone. Function Androgen (mainly testosterone) performs a variety of functions given below (a) It regulates the development, maturation and functions of male accessory sex organs like epididymis, vas deferens, seminal vesicles, prostate gland, urethra, etc. (b) These hormones also stimulate changes associated with puberty in males, i.e., muscular growth, growth of facial and axillary hair, aggressiveness, low pitch of voice, etc. (c) Also stimulates the process of spermatogenesis, i.e., formation of spermatozoa. (d) Promotes the growth of body tissues such as bones and muscles and helps in the formation of musculine body. (e) Also have anabolic effects (synthetic effects) on the metabolism of protein and carbohydrate. Inhibin Hormone Beside testosterone, another hormone is also secreted from testes by the Sertoli cells, known as inhibin. Its main function is to check and regulate the over activity of testosterone by inhibiting its secretion. Details about spermatogenesis, male reproductive system and hormones related to it will be studied in higher classes (i.e., class XII). Ovary It is the primary sex organ in females that serves to produce ova (female gametes) and female sex hormones. Location A pair of ovaries is located in the pelvic cavity (in the abdomen). Structure It is an almond-shaped structure. Internally it is composed of ovarian follicles and stromal tissues. Hormones Ovary produces two groups of steroid hormones, i.e., estrogen and progesterone. Estrogens are secreted by granulosa cells of Graafian follicle. After ovulation, the ruptured follicle is converted to another structure called corpus luteum, responsible for secretion of progesterone. Functions Both estrogens and progesterone play a vital role in various processes in female. These are as follows Estrogen (a) It helps in the growth of uterine endometrium layer during each menstrual cycle. (b) It directly influences the development of mammary glands. (c) Regulates female sexual behaviour and stimulate growth and activities of female secondary sex organs. (d) Plays a role in the development of growing ovarian follicles. (e) Appearance of female secondary sex characters (deposit of fat on thigh and hip region, high pitch etc.). Progesterone (a) It is secreted in very high amount continuously during pregnancy (i.e., supports pregnancy by forming placenta and preventing contractions in uterine wall). (b) It also acts on mammary glands and stimulates the formation of alveoli (sac-like structures that store milk) and milk secretion. (c) It also help in forming a mucus plug at cervix. Relaxin is another hormone secreted by ovary in the later stages of pregnancy. Its main role is in softening ligament, widening pelvic cavity, also affects other ligaments such as of foot etc. Due to which women may experience increase in their foot size during pregnancy. Various Tissue Hormones and Mechanism of Hormone Action Certain endocrine tissues are not organized to form compact endocrine gland, but are present isolated in the body, i.e., hormones are also secreted by some tissues. Some examples of hormones secreted by various tissues are as follows Hormones of Heart A very important peptide hormone known as Atrial Natriuretic Factor (ANF) is secreted by the atrial walls of our heart, when blood pressure is increased. Its secretion causes dilation of blood vessels thereby reducing the blood pressure. Hormones of Kidney A peptide hormone called erythropoietin is produced by the juxtaglomerular cells of kidney. This hormone stimulates formation of RBC, i.e., erythropoiesis. It is done by activating increased erythropoiesis in haemopoietic tissues. Hormones of Gastro-intestinal Tract GI tract develops from the endoderm of the embryo. Endocrine cells that are present in different parts of this and tract secretes four major peptide hormones. These are as follows (i) Gastrin, which acts on the gastric glands and stimulates the secretion of hydrochloric acid and pepsinogen. (ii) Secretin, which acts on the exocrine portion of pancreas (remember pancreas is a mixed gland, performing both exocrine and endocrine roles), stimulating secretion of water and bicarbonate ions. (iii) Cholecystokinin (CCK) This hormones acts on both pancreas and gall bladder stimulating secretion of pancreatic enzymes and bile juice respectively. (iv) Gastric Inhibitory Peptide (GIP), which is secreted by intestinal mucosa. Its function is to stop or inhibit the secretion of gastric juice and its motility into stomach. Apart from all these hormones, several other non-endocrine tissues secrete hormones known as growth factors. These factors are essential for normal growth, repair and regeneration of tissues. Mechanism of Hormone Action Hormones are released from their respective gland in very small amount. They carry out widespread effects in the body of an individual. Their response is very specific and accurate. Their effects are produced on target tissues by binding to the specific proteins known as hormone receptors, located in the target tissues only. Types of Hormones On the basis of the chemical nature, hormones are divided into following four groups (i) Peptide, Polypeptide, Protein Hormones (e.g., insulin, glucagon, pituitary hormones, hypothalamic hormones, etc). (ii) Steroids (e.g., cortisol, testosterone, estradiol and progesterone). (iii) Iodothyronines (e.g., thyroid hormones). (iv) Amino acid derivatives (e.g., epinephrine). Types of Hormone Receptors Hormone receptors are of two types (i) Membrane bound receptors Hormone receptors present on the cell membrane of the target cells. (ii) Intracellular receptors Hormone receptors present inside the target cell, e.g., Nuclear receptor (present in the nucleus of a cell). Action of Hormone Through Extracellular Receptor Hormones that interact with the membrane bound receptors do not enter their target cell in normal condition, but generate secondary messengers such as cyclic AMP (cAMP), IP3 , Ca2+ etc., which regulate cellular metabolism of the body. e.g., Protein or peptide hormone. Hormones do not participate in a metabolic reaction themselves, they instead acts as messengers only, i.e., primary messengers. Functioning of Peptide Hormone Protein hormone is water soluble in nature, binds to the extrinsic receptors (present on cell surface) to form the hormone-receptor complex. The formation of this complex causes the release of enzyme adenylate cyclase. This activated enzyme, thus leads to the formation of CAMP (i.e„ cyclic Adenosine monophosphate) from ATP in the cell from the receptor site. The hormone receptor complex changes the permeability of the cell membrane to facilitate the passage of materials through it (and thereby, regulates cellular activities of the cell causing specific response to occur). Generation of second messenger (cyclic AMP or Ca2+) chromosome function by interaction of hormone-receptor complex with the genome, e.g., Steroid hormone, iodothyronines, etc. Functioning of Steroid Hormone Steroid hormones are lipid soluble in nature, so they can easily diffuse through the cell membrane and bind to receptor molecules present in the cytoplasm to form a hormone-receptor complex that enters the nucleus. Action of Hormone Through Intracellular Receptors Hormones that interact with intracellular receptors are mostly involved in the regulation of gene expression . In nucleus, they bind to specific intracellular receptor site on chromosomes and regulate gene expression that results in physiological responses. Thus, the cumulative biochemical actions result in physiological and developmental effects. Antagonistic and Synergistic Interactions of Hormones Hormones can show both antagonistic and synergistic interactions among each other. In antagonistic interactions effects of two hormones are opposite to each other on the target cells, e.g., insulin and glucagon hormones, act antagonistically on blood glucose level. In synergistic interaction, two or more hormones tend to complement each other for their effect on target cells, e.g., estrogen, progestrone, oxytocin, prolactin all acts synergistically for the secretion, production and ejection of milk in mammary glands.

CLASS 11 CHAPTER 12 RESPIRATION IN PLANTS
https://acrobat.adobe.com/id/urn:aaid:sc:EU:d0c9346f-4120-4296-8d36-10b4bb5dedcb CLASS 11 CHAPTER 12 RESPIRATION IN PLANTS All living organisms require a continuous supply of energy for their survival. Energy is used to carry out various functions such as uptake of materials, absorption, growth, development, movement and even breathing. About 50% of the energy produced by the cell is utilized by these cellular activities and rest of it is changed into heat and get lost. Now, the question arises from where does this energy comes to carry out all these processes of life. Respiration : The Basics We eat food in order to obtain energy. The food we eat in the form of macro molecules is oxidized to fulfill energy requirement of body for caring out all the basic life processes. As we have already studied in last chapter, that only green plants and cyanobacteria can prepare their own food by the process called photosynthesis. They use trapped energy in order to obtain their food by converting light energy into chemical energy, which thereby gets stored into the bonds of carbohydrates such as glucose, sucrose, starch, etc. But all cells, tissues and organs in plants do not photosynthesize instead, photosynthesis takes place in only some parts of plants, i.e., only cells that contain chloroplasts (mostly areas located in superficial layers). Hence, all other organs, tissues and cells in green plant that are non-green are need food for oxidation. Hence, food has to be trans-located from the green parts to the non-green parts for oxidation processes. Need of Photosynthesis Animals on the other hand are heterotrophic in nature, i.e., they either obtain their food directly from the plants (herbivores) or indirectly, dependent on herbivores for their food (carnivores). Saprophytes are dependent on dead and decaying matter for their food (e.g., Fungi). Thus, it can be concluded that all the food that is respired for life processes ultimately comes from photosynthesis. Cellular Respiration Cellular respiration or the mechanism of breakdown of food materials within-the cell to release energy and trapping the same energy for synthesis of ATP. Respiration is the process of breaking of the C-C bonds of complex compounds through oxidation within the cells, leading to release of considerable amount of energy. It is to be noted that site of breaking down of complex molecules to yield energy is cytoplasm and mitochondria (also only in eukaryotes) which is different from the site of photosynthesis, which is chloroplast in plants. Respiratory Substrates The compounds that are oxidized during the process of respiration are called respiratory substrates. Carbohydrates are used as major respiratory substrates are oxidized in high amounts, to release energy, but under some conditions in some plants, proteins, fats and organic acids are also used as respiratory substrates. Differences between Respiration and Combustion ATP : Energy Currency of the Cell During the process of oxidation of food within a cell, all the energy contained in the respiratory substrates is not released free into the cell, or in a single step. Instead it gets released in a series of step-wise reactions controlled by enzymes and is trapped as chemical energy in the form of ATP. Hence, the energy released in respiration by the process of oxidation is not used directly but is used in synthesizing ATP (which is utilized whenever energy needs to be utilized). Thus, it is said that ATP acts as the energy currency of the cell. The energy trapped in ATP is utilized in many energy requiring processes of the organisms, and the carbon skeleton produced during respiration is used as precursors for the biosynthesis of other molecules in a cell. Do Plants Breathe : Exchange of Gases in Plants For the process of respiration, plant takes O2 and releases CO2. Plants have stomata and lenticles for gaseous exchange instead of specialized organs that are present in animals for exchange of gases. Following are the reasons which shows, how plants can get along without respiratory organs (i) Every part of the plant has the ability to take care of its own needs of gas exchange and also very little transport of gases occur from one part of the plant to another. (ii) It is only during the process of photosynthesis that large volumes of gases are exchanged and each leaf of the plant has ability to take care of its own needs during these periods. Thus, when cells photosynthesis, availability of O2 is not a problem in these cells due to a continuous release of O2 that takes place within the cell. (iii) Gases may easily diffuse in large, bulky plants as distance for diffusion is not so great because living cells in a plant are located quite close to the surface of the plant. In case of stems, which are thick and woody in nature, the organization of living cells is in the form of thin layers, which are found inside and beneath the bark. Like leaves which have stomata for gaseous exchange, these stems also have openings called lenticels. Internal cells are dead and provide only mechanical support to the plant. This depicts that most cells of plant have atleast a part of their surface in contact with the air. The loose packing of parenchyma cells in leaves, stems and roots and provides an interconnected network of air spaces helps in facilitating this process. Types of Respiration We know that during the process of respiration, utilization of O2 takes place with the release of CO2, water and energy as products. According to the dependence of cells on oxygen, cellular respiration may be classified into two types as given below 1 Aerobic Respiration This is the type of respiration in which organism utilize oxygen for the complete oxidation of organic food into CO2 and water. It occurs inside the mitochondria. Aerobic respiration yields more energy as the respiratory substrate gets completely oxidized in the presence of O2. 2. Anaerobic Respiration This is the type of respiration in which organic food is oxidized incompletely without utilizing energy as oxidant. It occurs in cytoplasm and often releases small amount of energy. It is believed that the first cells on this planet lived in an oxygen free environment, i.e., they were anaerobes. Even among present day living organisms, several are adapted to anaerobic conditions. Some of them are facultative anaerobes (organisms that have capability of switching from aerobic to anaerobic conditions according to the availability of oxygen) while others are obligate anaerobes (organisms that are killed by normal atmospheric concentration of oxygen of 21%). Thus, in any case, all living organisms retain the enzymatic machinery for partial oxidation of glucose in the absence of oxygen. And this breakdown of glucose to pyruvic acid is called glycolysis. Respiration: The Mechanism Cellular respiration occurs inside the cell and proceeds with the help of enzymes. The first step in respiration (taking glucose as substrate) is the glycolysis (glucose oxidized to pyruvic acid). After which the pyruvic acid may enter the Krebs’ cycle (aerobic respiration) or undergo fermentation (anaerobic respiration). Glycolysis Glycolysis (Gr. Glycor-sugar; lysis-splitting), is a step-wise process by which one molecule of glucose (6C) breaks down into two molecules of pyruvic acid (3C). The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof and J Parnas and is often referred as the EMP pathway. It is a common pathway in both aerobic and anaerobic modes of respiration. But in case of anaerobic organisms, it is the only process of respiration. Glycolysis occurs in the cytoplasm of the cell. During the process glucose gets partially oxidized. In plants this glucose is derived from sucrose (end product of photosynthesis) or from storage carbohydrates. During the course of process in plant this sucrose is first converted into glucose and fructose by the action of invertase enzyme after this, these two monosaccharides enter the glycolytic pathway. Steps Involved in Glycolysis In glycolysis, a chain of 10 reactions often reactions occur under the control of different enzymes. It involves the following steps Step I Phosphorylation of glucose occur under the action of an enzyme hexokinase and Mg2+ that gives rise to glucose-6-phosphate by the utilization of ATP. Step II Isomerisation of this phosphorylated glucose-6-phsophate takes place to form fructose-6-phosphate with the help of an enzyme phosphohexose isomerase (Reversible Reaction). Step III This fructose-6-phosphate is again phosphorylated by ATP in order to form fructose 1, 6-bisphosphate in the presence of an enzyme phosphofructokinase and Mg2+. The steps of phosphorylation of glucose to fructose 1, 6-bisphosphate (i.e., from step 1 to 3) activates the sugar thus, preventing it from getting out of the cell. Step IV Splitting of fructose 1, 6-bisphosphate takes place into two triose phosphate molecules, i.e., dihydroxyacetone 3-phosphate and 3-phosphoglyceraldehyde (i.e., PGAL). This reaction is catalyzed by an enzyme aldolase. Step V Each molecule of PGAL removes two redox equivalents in the form of hydrogen atom and transfer them to a molecule of NAD+ (This NAD+ forms NADH + H+) and accepts inorganic phosphate (Pi) from phosphoric acid. This reaction in turn leads to the conversion to PGAL (which gets oxidized) to 1, 3-bisphosphoglycerate (BPGA) (Reversible reaction). Step VI 1, 3-bisphosphoglycerate is converted to 3-phosphoglycerate with the formation of ATP. This reaction is catalyzed by an enzyme phosphoglycerate kinase. It is also known as energy yielding process. The formation of ATP directly from metabolites constitutes substrate level phosphorylation (Reversible reaction). Step VII In the next step, 3-phosphoglycerate is subsequently isomerised to form 2-phosphoglycerate, catalyzed by enzyme phosphoglycero-mutase (Reversible reaction). Step VIII In the presence of enzyme enolase and Mg2+, with the loss of a water molecule,2-phosphoglycerate is converted to Phosphoenol Pyruvate (PEP) (Reversible reaction). Step IX High energy phosphate group of Phosphoenol Pyruvate (PEP) is transferred to a molecule of ADP, by the action of enzyme pyruvate kinase in the presence of Mg2+ and K+ This in turn produces two molecules of pyruvic acid (pyruvate) and a molecule of ATP by substrate level phosphorylation. The pyruvic acid thus, produced is the key product of glycolysis. Metabolic Fate of Glycolysis The overall reaction of glycolysis can be depicted as * Glucose + 2Pi + 2ADP + 2NAD+ —> 2 Pyruvate + 2ATP + 2NADH + 2H+ * Two molecules of NADH on oxidation produce 6 molecules of ATP. Therefore, a net gain of 8ATP molecules occurs during glycolysis. * The fete of glycolysis depends upon the availability of oxygen in the cell. In the presence of oxygen, pyruvic acid will enter the mitochondrion and undergo complete oxidation of glucose to CO 2 andH20 in aerobic respiration (Krebs’ cycle). * On the other hand in the absence of oxygen, the pyruvic acid will undergo anaerobic respiration (lactic acid fermentation or alcoholic fermentation). Fermentation Various microorganisms, bacteria, animals and plants are known to catabolizse pyruvic acid into various organic compounds depending upon the specific enzymes they possess. Some of these types are as follows (i) During alcoholic fermentation, in fungi (e.g., yeast), and some higher plants, the incomplete oxidation of glucose is achieved under anaerobic condition by a series of reactions in which pyruvic acid is converted to CO2 and ethanol. It is done under two steps (а) Pyruvic acid is first decarboxylated to acetaldehyde in the presence of enzyme pyruvic acid decarboxylase. (b) This acetaldehyde is further reduced to ethyl alcohol or ethanol in the presence of enzyme, i.e., alcohol dehydrogenase. (ii) During lactic acid fermentation, organisms like some bacteria produces lactic acid as an end product from pyruvic acid. During the reduction, the pyruvic acid produced in glycolysis is reduced by NADH2 to form lactic acid, CO2 is not produced and NADH2 is oxidized to NAD+.This reaction is catalyzed by an lactic acid dehydrogenase, FMN proteins and Zn2+ ions. Likewise, in case of animal cells also (such as muscles) during exercise, when there is inadequate amount of oxygen for cellular respiration, pyruvic acid is reduced to lactic acid by lactate dehydrogenase. Thus, in both the processes re-oxidation of reducing (NADH + H+) agent takes place. Energy Yield in Fermentation In both alcoholic and lactic acid fermentation, the energy released is very less, i.e., not more than 7% of the energy is released from glucose and not all of it is trapped as high energy bonds of ATP. Also, the fermentation processes are proved to be hazardous in nature because either acid or alcohol is produced on oxidation. Apart from this, yeasts may also poison themselves to death if the concentration of alcohol reaches about 13%. Drawback of this process is that organisms cannot carryout complete oxidation of glucose and are also unable to extract out the energy stored to synthesize a larger number of ATP molecules required for cellular metabolism. Differences between Glycolysis and Fermentation Aerobic Respiration Aerobic respiration is the next step (after glycolysis) that leads to complete oxidation of organic substances. It occurs in the presence of oxygen. The oxygen acts as a final acceptor of electron and protons are removed from the substrate. For aerobic respiration to take place within the mitochondria, the final product of glycolysis, i.e., pyruvic acid is transported into from the cytoplasm mitochondria and thus, the second phase of respiration is initiated. The process of aerobic respiration involves two crucial events (i) The complete oxidation of pyruvate occurs by the step-wise removal of all the hydrogen atoms, thereby, leaving three molecules of CO2. This occurs in the matrix of mitochondria. (ii) The electrons removed as part of the hydrogen atoms are then passed on to molecular 02 with the simultaneous synthesis of ATP. This on the contrary takes place on the inner membrane of the mitochondria. Oxidative Decarboxylation of Pyruvic Acid In mitochondria, pyruvic acid (formed by the glycolytic catabolism of carbohydrates in cytosol) undergoes oxidative decarboxylation (i.e., removal of CO2 in aerobic conditions) forming a key compound, i.e., acetyl Co-A by the action of pyruvic acid dehydrogenase (in mitochondrial matrix) through a series of reactions. Thus, acetyl Co-A acts as a connecting link between glycolysis and citric acid cycle. During this process, two molecules of NADH are produced from the metabolism of two molecules of pyruvic acid (produced from one glucose molecule during glycolysis). Tricarboxylic Acid (TCA) Cycle or Krebs’ cycle: The acetyl Co-A then enters a cyclic pathway, Krebs’ cycle (or tricarboxylic acid cycle, TCA) in mitochondrial matrix. Various coenzymes including NAD+ and Co-A also participates in the reaction catalyzed by pyruvic acid dehydrogenase. It was first elucidated by Sir Hans Kreb, a British Biochemist in 1940. The whole cycle explains how pyruvate is broken down to CO2 and water. Following are the steps of Krebs ’ cycle (i) Condensation The Krebs’ cycle starts with the condensation of acetyl group with oxaloacetic acid and water to yield citric acid, a 6C compound. This is the first stable product of the cycle. This step is catalyzed by an enzyme citrate synthetase. Co-A is liberated during this reaction. (ii) Citric acid then undergoes re-organization in two steps in order to form in the presence of an enzyme acinotase. intermediate (iii) Oxidative decarboxylation Isocitrate is followed by two successive steps of oxidative decarboxylation, that leads to the formation of a-ketoglutaric acid, (a 5C compound in the presence of an enzyme isocitrate dehydrogenase and Mn1 ) and then succinyl Co-A, catalyzed by a-complex. . The succinyl Co-A then splits into a 4C compound succinic acid and Co-A with the addition of water. During this conversion, a molecule of GTP (guanosine triphosphate) is synthesized catalyzed by an enzyme succinyl Co-A synthetase (this occurs when co-enzyme A transfers its high energy to a phosphate group that joins GDP forming GTP). (i) GTP is also an energy carrier like ATP. Thus, this is the only high energy phosphate produced in the Krebs’ cycle. (ii) In plants cells, this reaction also produces ATP from ADP. In the remaining steps of Krebs’ cycle, succinyl Co-A is oxidized to oxaloacetic acid, a 4C compound following the formation of fumaric acid and malic acid catalyzed by enzymes succinate dehydrogenase and fumacase respectively. Output of Krebs’ Cycle or Citric Acid Cycle During this cycle of reactions, 3 molecules of NAD+ are reduced to NADH + H+, and one molecule of FAD+ is reduced to FADH2. And also one molecule of ATP is reduced directly from GTP (by substrate level phosphorylation). For continuous oxidation of acetyl Co-A, continued replenishment of oxaloacetic acid is necessary. In addition to this regeneration of NAD+ and FAD+ from NADH and FADH2 respectively are also required. The summary equation for this phase of respiration is as follows Till now, glucose has been broken down to release CO2 and 8 molecules of NADH+H+, two FADH2 are synthesized and just two molecules of ATP. Importance of Citric Acid Cycle The citric acid cycle is important in the following ways (i) This is the major pathway for the formation for ATP molecules. (ii) Many intermediate compounds of this cycle are used in the synthesis of other biomolecules. Differences between Glycolysis and Krebs’cycle Aerobic Respiration In this process, the complete oxidation of organic substances takes place in the presence of oxygen, releasing water, carbon dioxide and an enormous amount of energy found in the substrate. Aerobic respiration is most commonly found in higher organisms. For it to occur inside the mitochondria, the ultimate product of glycolysis, pyruvate is moved from the cytoplasm into the mitochondria. Some important events taking place are:  complete oxidation of pyruvate, leaving 3 molecules of CO2  passing electrons eliminated as part of hydrogen atoms to molecular oxygen with a parallel synthesis of ATP Electron Transport System(ETS) and Oxidative Phosphorylation Found in the inner mitochondrial membrane, the electron transport system(ETS) is the metabolic pathway through which electrons pass from one carrier to another. The illustration below provides more details. In the Electron Transport System step, takes place in the inner mitochondrial membrane to activate the proton pump and then finally the oxidative phosphorylation of ADP takes place to form the ATP in the presence of oxygen which accepts the electron to generate water. The electron transport chain contains the accompanying:  Complex I: NADH dehydrogenase  Complex II: succinate dehydrogenase  Complex III: cytochromes bc 1  Complex IV: cytochromes a-a3  Complex V: ATP synthase NADH2 is oxidized by NADH dehydrogenase and electrons are then moved to ubiquinone situated in the inward mitochondrial film. FADH2 is oxidized by succinate dehydrogenase and moved electrons to ubiquinone. The decreased ubiquinone is then oxidized with the move of electrons by means of cytochromes bc 1 complex to cytochrome c. Cytochrome c is a little protein joined to the external surface of the internal film and moves electrons from complex III to complex IV. At the point when electrons moved to start with one transporter and then onto the next by means of mind-boggling I to complex IV, they are coupled to ATP amalgamation of ATP from ADP and Pi (inorganic phosphate) Oxygen assumes an essential part in eliminating electrons and hydrogen particles lastly help in the development of H₂ Oxidative Phosphorylation Oxidative phosphorylation is the terminal oxidation of high-impact breath. It is the cycle where ATP is shaped with the assistance of electrons moved from the electron transport chain. F1 molecule is the site of oxidative phosphorylation. It contains an ATP synthase catalyst. At the point when the convergence of proton is higher at F0 than in F1 molecule, ATP synthase became dynamic for ATP blend. The energy from the proton slope is utilized to append the phosphate radical and ADP by high energy bond to produce ATP Respiratory Balance Sheet The net gain in ATP per glucose molecule is calculated theoretically using the respiration balance sheet. One mole of glucose is converted into 38 ATP during the entire process.  In glycolysis; 1 ATP + 2 NADH2 (=6 ATP) = 8 ATPs  In Oxidative decarboxylation; 2 NADH2 = 6 ATPs  In Krebs Cycle; 2 GTP (2 ATP) + 6 NADH2 (=18 ATP) + 2 FADH2 (= 4ATP) = 24 ATPs  Total ATPs generated during aerobic respiration = 38 ATPs – 2 ATPs utilized during glycolysis = 36 ATPs  Total ATPs generated during anaerobic respiration = 2 ATPs Amphibolic Pathway Respiration is considered an amphibolic pathway in which both anabolism and catabolism are involved. As glucose is the favorable substrate of respiration carbohydrates, fats, and proteins are first converted into glucose or related product and then enters the pathway. Respiratory Quotient The respiratory quotient refers to the actual volume of carbon dioxide removed to the actual volume of oxygen used during the process of cellular respiration. The respiratory ratio is another name for it. RQ designates it. RQ=volume of carbon dioxide eliminate/ The volume of oxygen consumed The type of respiratory substrate employed during the act of respiration affects the respiratory quotient. In addition, the respiratory quotient, which is derived from carbon dioxide generation, is a dimensionless number utilized in the estimation of the basal metabolic rate, or BMR. The respiratory quotient reaches zero when the substrate of carbohydrates is completely oxidized. Here, the amount of carbon dioxide released and the amount of oxygen absorbed is equal. C6H12O6 + 6O2 ———-> 6CO2 + 6H2O+ energy RQ=6CO2/ 6O2 Carbohydrates have an RQ of about 1 Additionally, fats contribute to cellular respiration. In contrast to carbohydrate molecules, fat molecules undergo partial oxidation. The respiratory quotient is, therefore, lower than. 2(C51H98O6) + 145O2 —————> 102CO2 + 98H2O + energy RQ=102CO2/145O2=0.7 Fats have an RQ of about .70 Proteins have an RQ of about 0.9 Comparison Between Fermentation and Aerobic Respiration  Where aerobic respiration is the complete degradation of carbon dioxide and water, fermentation results in the partial breakdown of glucose only  Aerobic conditions lead to the formation of several molecules of ATP, whereas the net gain of only two molecules of ATP is observed for each molecule of glucose degraded to pyruvic acid in the process of fermentation.  In fermentation, NADH is oxidized to NAD+ slowly, whereas this same reaction is vigorous under aerobic conditions.

CLASS 11 CHAPTER 9: BIOMOLECULES
https://acrobat.adobe.com/id/urn:aaid:sc:EU:0a06db24-9108-4fbc-bfb6-5415c2c849c0 CLASS 11 CHAPTER 9: BIOMOLECULES A cell is composed of variety of molecules (like carbon, hydrogen, oxygen) which perform various functions. Other than these basic elements, some metals and non-metals are also present as cellular materials, thence, all these materials combines in different ways in order to form various biomolecules, which are found in cells of organisms. These molecules are not living, but perform various living functions. Thus, biomolecules are the organic substances (e.g., Carbohydrates, proteins, lipids, etc.) that play a major role in the structure and function of the living organism. Water is also an important and most abundant chemical compound present in the body of living organism. Cellular Pool The sum total of different types of biomolecules, compounds and ions present in the cell is called cellular pool. It contains more than 5000 chemicals. List of Representative Inorganic Constituents of Living Tissues Components Formula Biomicromolecules: Biomicromolecules are small in size, with low molecular weight (18-1800 Da) highly soluble (if polar) and have simple molecular conformation. Micro-molecules can be inorganic such as water, minerals salts, gases or organic compounds such as sugars, amino acids, nucleotides, etc. All these compounds mentioned above are soluble fraction of filtrate except the lipids which occur as insoluble fraction of filtrate as they are mostly found in cell membrane and thereby forms vesicles, which are separated as an insoluble pool. Various micro-molecules in detail are as follows 1. Carbohydrates These are the organic compound mainly made up of C, H and O. They are defined as polyhydroxy aldehydes and ketones. These are produced directly by the plants during photosynthesis. Carbohydrates are also known as saccharides because their major constituents are sugars. These are divided into following types i- Monosaccharides These are simplest carbohydrates which cannot be hydrolyzed further into smaller components. These are generally composed of three to seven carbon atoms per molecule. Monosaccharides are also known as reducing sugars, because they have a free aldehydic (—CHO) or ketonic (> C = O) group and can also reduce Cu2+ (cupric ions) of Benedict’s or Fehling’s solution to Cu+ (cuprous ions)., e.g., Ribose, glucose, erythrose, etc. 1. Oligosaccharides These are formed by condensation of 2-6 monosaccharides molecules. The bond between two monosaccharides units is called a glycosidic bond. They are classified according to the number of their monosaccharides units or monomers as follows (a) Disaccharides These are the sugars containing two monomeric units and can be further hydrolysed into smaller components. These are known as non-reducing sugars because the free aldehyde or ketone group is absent, e.g., Sucrose, maltose, lactose, etc. (b) Trisaccharide It contain three monomers. e.g., Raffinose. (c) Tetrasaccharides, e.g., Stachyose and so on. 2 Amino Acids Amino acids are organic compounds containing an amino group and an acidic group as substituent on the same carbon, i.e., the a-carbon. Hence, they are called a-amino acids. These are substituted methanes. a-carbon also bears a hydrogen and a variable group designated as R group. Thus, there are four substituent groups present on a-carbon which occupy the four different valency position. These are hydrogen, carboxyl, amino and R group. Based on the nature of R group, there are many amino acids. However, those which occur in proteins are only of twenty types. The amino group accepts a proton whereas, the carboxyl group donates a proton. So, an amino acid can act as both acid and base. Hence, it is amphoteric in nature. The R group in these proteinaceous amino acids could be a hydrogen (glycine), a methyl group (alanine), hydroxyl methyl (serine), etc. The chemical and physical properties of amino acids are essentially due to the amino, carboxyl and functional groups present. Based on the number of amino and carboxyl group present, amino acids are categorized into following types i. Acidic Amino Acids These contain one amino group and two carboxyl group per molecule, e.g., glutamic acid and aspartic acid. ii. Basic Amino Acids These contain two amino groups and one carboxyl group per molecule, e.g., Arginine, lysine and histidine. iii. Neutral Amino Acids These contain one amino group and one carboxyl group per molecule, e.g., Methionine, isoleucine, serine, threonine, cysteine, glycine, alanine, valine, leucine, aspargine, glutamine and proline. iv. Aromatic Amino Acids These contain aromatic rings in their side chain, e.g., Phenylalanine, tyrosine and tryptophan. Zwitter Ion: Zwitter ion formation is another particular property of amino acid. It is a neutral molecule (with positive and negative charge), having the ionizable nature of —NH2 and —COOH groups. Hence, in solutions of different pHs, the structure of amino acid changes variably. 3. Lipids Lipids are the esters of fatty acids and alcohol. These are generally insoluble in water. They could be simply fatty acids. Fatty acids are the organic acids having hydrocarbon chains that end in a carboxylic group (—COOH). The carboxylic group is attached to an R group that could be a methyl (—CH3) or ethyl (—C2H5) or higher number of —CH2 groups (1 carbon to 19 carbons), e.g., Palmitic acid has 16 carbons including carboxyl carbon. Arachidonic acid has 20 carbon atoms including the carboxyl carbon. Depending upon the types of bonds present, fatty acids are of following two types i.Saturated Fatty Acids Fatty acids which do not have double bonds, (C—C). These are generally solid at room temperature. ii. Unsaturated Fatty Acids Fatty acids which contain one or more than one double bonds (C = C). These are generally liquid at room temperature. Difference between saturated and unsaturated fatty acids Simple Lipids These are esters of fatty acids and various alcohol. They are of further two types (a) Neutral or True Fats These are esters of fatty acids with glycerol (glycerine). They are also called glycerides. Glycerol is a simple lipid which is known as trihydroxypropane as it is an alcohol with a backbone of three carbon atoms, each carrying an —OH group. When glycerol is esterified with fatty acid it is known as triglyceride. The ester is called monoglyceride, diglycerlde and triglyceride depending on the number of fatty acids attached to a glycerol. ii- Compound or Conjugated Lipids These are the esters of fatty acids and alcohol but contain other substances also, e.g., Phospholipids, glycolipids, cutin, suberin etc. Phospholipids are lipids which have phosphorus and phosphorylated organic compound in them. One of the common example of phospholipid is lecithin. Some tissue have complex structure of lipids, e.g., Neural tissues. (b) Oils are usually liquid at room temperature because they have low melting point, e.g., groundnut (peanut) oil, cotton seed oil, mustard oil, etc. As oils have low melting points. They remain as oils in winters also, e.g., Gingely oil. iii. Derived Lipids These are lipid-like substances such as sterol or derivatives of lipids, e.g., steroids, prostaglandins and terpenes. Fats are also differentiated into two main types, on the basis of their melting points at room temperature as follows (a) Hard Fats are solids at room temperature and contain long chains of fatty acids, e.g., Animal fat. Softness of butter is due to the good quantity of short chain fatty acid it contains. 4. Nucleotides These are the monomers of nucleic acids.The nucleotides are made up of three molecules, i.e., a pentose sugar, a cyclic nitrogenous base and a phosphoric acid (phosphate group), e.g., Adenylic acid, thymidylic acid, guanylic acid, uridylic acid and cytidylic acid. 1. Pentose Sugar It occurs in pentagon or furanose form with four carbon and one 02 forming a ring. It is present in the form of ribose or deoxyribose sugar in RNA and DNA respectively. i. Nitrogenous Bases These are the flat heterocyclic compounds having nitrogen and carbon in ring structure. These are of basically two types (a) Purines It is larger and composed of two rings. They are further of two types, i.e., Adenine (A) and Guanine (G). (b) Pyrimidines It is smaller and composed of single ring. They are of further three types, i.e., Cytosine (C), Thymine (T) and Uracil (U). iii. Phosphoric Acid (Phosphate Group) It is composed of phosphoric acid. A nucleotide may have 1, 2 or 3 phosphate groups. It gives acidic nature to the nucleotide. Nucleoside If a pentose sugar is attached to a nitrogen base by a glycosidic bond, it is called nucleoside. e.g., adenine + ribose —> adenosine. Likewise guanosine, thymidine, uridine and cytidine are the examples of nucleoside. The nucleoside combines with a phosphate group at 5-position by an ester bond to form a nucleotide. Differences between Nucleoside and Nucleotide Primary and Secondary Metabolites A large number of organic biomolecules are present in the cells which are used in various metabolic reactions of cell. Hence, these compounds are called metabolites. These are divided into two types 1. Primary Metabolites These are metabolites which are found in animal tissues. Their functions are easily indentifiable. They play specific known roles in the normal physiological processes, e.g., Amino acids, carbohydrates, proteins, nitrogen bases, nucleic acids, etc. 2. Secondary Metabolites These are metabolites which are generally found in plant, fungal and microbial cells. These are the products of certain metabolic pathways. Their functions are not identifiable in host organism and are not yet understood, e.g., Alkaloids, flavonoids, rubber, essential oils, antibiotics, coloured pigments, scents, gums, spices. Some Secondary Metabolites Note: * Nucleic acids (DNA and RNA) are composed of only nucleotides, both DNA and RNA acts as a genetic material. * Uracil is found only in RNA in place of thymine. * Ribose molecule differs from deoxyribose molecule in having a -OH group instead of H at carbon 2. * Heterocyclic compounds have more than one kind of atoms. Functions Both primary and secondary metabolites serves the following junctions (i) Many of them are useful in human welfare, e.g., Rubber, drugs, spices, scents, pigments. (ii) Some have ecological importance. Biomacromolecules: Biomacromolecules are large in size, higher molecular weight molecules 10,000 daltons (Da) and above (except lipids). These are generally formed by linking a number of micromolecules commonly known as monomers. All these compounds are found in the acid insoluble pool. These are of four major types, i.e., proteins, polysaccharides, nucleic acids and lipids. Except lipids all other macromolecules are formed by polymerization (condensation) of monomeric sub-units. The molecules which are found in living organisms are divided into two main types (i) Biomicromolecules These are molecules which have their molecular weight less than 10,000 Da. Biomicromolecules has already been described in detail in topic 1 of the chapter. . (ii) Biomacromolecules These are molecules which have their molecular weight, 10,000 Da and above. All these macromolecules are actually polymers of their biomicromolecules. For example, Poly saccharides are polymers of monosaccharides, proteins are polymers of amino acids and nucleic acids are polymers of nucleotides. Hence, on the basis of the number and types of monomer present, polymers are of following two types (i) Homopolymers, are those which have only one type of monomer present. These monomer can be repeated n number of times in a chain, e.g., Starch, insulin, etc. (ii) Heteropolymers, are those which have two or more than two types of monomers, e.g., Proteins.Various macromolecules and their major roles are described under as Lipids The molecules in the insoluble fraction are polymeric substances except lipids. Athough lipids have their molecular weight not exceeding above 800 Da, but still it comes under acid insoluble fraction, i.e., biomacromolecular category. This happens because these are small moleculer weight compounds and are present not only as such, but also arranged in structures like cell membranes and other membranes. Thus, when we grind a tissue, we disrupt the cell structure, cell membrane and other membranes are broken down into pieces and form vesicles that are not water soluble. Therefore, these are separated along with acid insoluble pool and are placed in macromolecules. Lipids are not strictly biomacromolecule. If representation of the chemical- composition of living tissue is done from abundance point of view and arranged class-wise, it is observed that water is the most abundant chemical in living organisms. Average Composition of Cells i. Primary Structure It is the description of basic structure of a protein. This includes number and sequence of amino acids in each polypeptide. The distance between two adjacent peptide bonds is about 0.35 nm. A protein is imagined as a line whose left end is represented by the first amino acid, also called as the N-terminal amino acid and the right end is represented by the last amino acid called the C-terminal amino add, e.g., Insulin, ribonucleases. Proteins These are the most important and abundant intracellular organic biomolecules. These are polypeptides having chains of amino acid arranged linearly that are linked by peptide bonds. Thus, each protein is a polymer of amino acids (as studied earlier in the chapter), there are 20 types of amino acids, e.g., Alanine, valine arginine, leucine, histidine, etc. So, proteins are considered as heteropolymer. These amino acids are divided into two main types, on the basis of their utility (i) Essential Amino Acids: These are those amino acids that are essential for our health so, are need to be supplied through our diet. The dietary proteins are the source of essential amino acids, e.g., Leucine, isoleucine, etc. (ii) Non-essential Amino Acids: These are those amino acids, which our body can synthesize, e.g., Proline, serine. Human adults require an additional essential amino acid named threonine while children need two more arginine and histidine. These are. called semi-essential amino acids. Structure of Proteins As mentioned earlier, proteins are heteropolymers containing strings of amino acids. Biologists describe the protein structure at four different levels, i.e., primary, secondary, tertiary and quaternary. ii. Secondary Structure The thread of the primary protein is folded in the form of a-helix. The a-helix is stabilized by hydrogen bonds between oxygen of the carboxylic group of one amino acid residue and —NH group of the next fourth amino acid residue, e.g., Keratin. In β-pleated secondary structure, two or more polypeptide chains get interconnected by hydrogen bonds. Adjacent strands of polypeptide may run in the same direction or in opposite direction, e.g., Silk fibre. In proteins, only right handed helices are observed.The polypeptide chain curls The protein is more distended and longitudinally by the action of the hydrogen bond forms a zig-zag hydrogen bonds forming a shaped protein structure called spiral or helix. (which combines and forms p-sheet). Differences between α-helix and β–pleated Structure of Proteins iii. Tertiary Structure There is bending and folding of various types to form a hollow wollen ball-like spheres, rods or fibres. Tertiary structure is stabilized by several types of bonds-hydrogen bonds, ionic bonds, Van der Waal’s interactions, covalent bonds and hydrophobic bonds. It gives information about a 3-dimensional (3-D) conformation of the protein, e.g., Myoglobin. Tertiary structure is helpful for many biological activities of proteins. iv. Quaternary Structure Certain proteins consist of an assembly of more than one polypeptide or sub-units. Thus, the individual polypeptide or subunit are arranged with respect to one another (linear strings of spheres, spheres arranged one upon each other in the form of a cube or plate, etc.) e.g., Haemoglobin, lactic acid dehydrogenase enzyme. This type of structure is found only in the oligomeric proteins (proteins having two or more polypeptide chains). Structure of Haemoglobin (Hb) An adult human haemoglobin is a iron containing pigment that acts as an oxygen carrier. It has a quaternary structure because it is made up of four monomeric sub-units each about the size of many normal individual proteins. Every subunit has its own tertiary structure and is identical to each other. Hence, two sub-units of α-type and two sub-units of β-type together constitute the human haemoglobin (Hb). Insulin is an another example of protein having quaternary structure. Types of Proteins Proteins are classified on the basis of shape, chemical composition and function. Accordingly on the basis of shape these are of two main types i. Fibrous Proteins The proteins have spiral secondary polypeptide chains wound around each other in order to form fibres. These are insoluble in water generally, but soluble in concentrated acids, alkalis and salts, e.g., Collagen of connective tissue, keratin of hair, etc. ii. Globular Proteins They are rounded in shape and are generally soluble in water and in dilute acids, alkalis, salts, e.g., Egg albumin, serum globulins. Note: Collagen, the most abundant protein of animal world and Ribulose Bisphosphate Carboxylase Oxygenase (RuBisCO) is the most abundant protein in plants and the whole of the biosphere. Functions of Proteins Proteins have various basic functions in living organism given below . Helps in transportation of nutrients across the cell membrane by acting as protein transporter. (ii) Helps in fighting with infectious organism. (iii) These are helpful in movement of muscles, e.g., Myosin and actin. (iv) Helps in maintenance of pH and regulation of the volume of body fluids. (v) Helps at the time of injury in blood clotting and acts as antibodies and provide immunity. (vi) Helps in growth and repair of body tissues. (vii) Some proteins function as hormones and some functin as enzymes and catalyse the reactions. Denaturation of Proteins When proteins are exposed to extreme change in pH, acids or temperature (or bases or high salt concentrations) the weak bonds holding the tertiary and the quaternary structure gets disrupted so, that the protein unfold (into primary structure). This unfolding is known as denaturation of proteins or loss of its functioning. Denaturation is not strong enough to break peptide bonds thus, primary structure remains unaffected. A denatured protein may spontaneously refold into its original structure when suitable condition are re-provided. This is called renaturation. Polysaccharides These are another class of macro-molecule that are present in the acid insoluble fraction. Poly saccharides are long chains of sugars. They are not sweet and are insoluble in water. Polysaccharide chain (like glycogen) is made up of two ends, whose right end is called reducing end and the other left end is called non-reducing end. They- ace threads containing different monosaccharides as building blocks. Types of Poly saccharides Poly saccharides are of two types as given below i. Homopolysaccharides These are those complex carbohydrates which are formed by polymerization of only one type of monosaccharides monomers, e.g., Starch, glycogen and cellulose (these all are composed of single type of monosaccharides unit namely glucose). Some of them are as fallows a. Cellulose It is a polymeric polysaccharide which consists of only one type of monosaccharides monomer, i.e., glucose. It is known to be a rigid and insoluble polysaccharide found in cell wall of most algae, certain protists, fungi and some higher plant. Paper made from pulp of plant and cotton fibre are also made up of cellulose. As cellulose is not composed of complex helices so, it cannot hold iodine (I2) and cannot give colour with iodine. b. Starch It is a storage polysaccharide because it helps in storing energy in plant tissues. Chemically, the starch is formed of two glucose monomers, r.e.,α-amylose and amylopectin. Starch forms helical secondary structures. Thus, it can hold iodine (I2) molecules in the helical portion. Therefore, gives blue colour with iodine solution. c. Glycogen It is also storage polysacchiaride found in animals only (in liver cells and muscles). It is also known as animal starch. It gives red colour on reaction with iodine. It is a polymer of fructose. It is a naturally occurring polysaccharide produced by many types of plants. It is used by some plants in storing energy. Plants that synthesis and store inulin are unable to store other forms of carbohydrates like starch, etc. Agar, xylan, araban, etc, are some other types of homopolysaccharides found. ii. Heteropolysaccharides These are complex carbohydrates formed by the polymerization of two or more than two types of monosaccharide monomers, e.g., Chitin, pectin, peptidoglycans (murein), hyaluronic acid. iii. One of them is explained below Chitin It is the second most abundant natural polymer, found in exoskeleton of arthropods (e.g., prawns, crabs, etc.) and in cell wall of fungi. It has building blocks of amino sugars and chemically modified sugar. iv. Acetylglucosamine units interlinked by glycosidic bond Glucosamine also acts as building block (like N-acetyl glucosamine) in other types of heteropolysaccharide. Functions of Polysaccharide Polysaccharide plays multiple function and can be used in the following ways (i) Acts as structural compounds in cell wall of plants certain fungi and protists, e.g., Cellulose, chitin. (ii) Helps in anticoagulation and prevents blood clotting inside the vessels, e.g., Heparin. (iii) Helps in lubrication of joints between bones, e.g., Hyaluronic acid. (iv) Also used in tissue culture, e.g. Agar. (v) Acts as a reserve food, e.g., Starch. Nucleic Acids The other type of macromolecule found as a part of acid insoluble fraction of any living tissue is the nucleic acids. These are polymeric compounds of nucleotides, i.e., polynucleotides. A nucleotide (as discussed previously in the chapter) is composed of three chemically distinct components (i) Heterocyclic compound-nitrogen base (adenine, guanine, uracil, cytosine and thymine). (ii) Monosaccharide (ribose or deoxyribose). (iii) Phosphoric acid or phosphate. A nucleic acid which contains deoxyribose sugar is called deoxyribonucleic acid (DNA), while that which contains ribose sugar is ribonucleic acid (RNA). Deoxyribonucleic Acid (DNA) DNA is genetic material found in the nucleus of all living cells except some viruses. In eukaryotic organisms linear DNA is found in nucleus, in the mitochondria and chloroplasts, whereas in prokaryotes, DNA is circular in structure and is found in the cytoplasm. Structure of DNA The structure of DNA was elucidated by Watson and Crick based on X-ray diffraction studies. They proposed a double helix model of DNA. According to this model, DNA exists as a double helix and consists of two strands of polynucleotides that are antiparallel to each other, i.e., both run in opposite directions, one in 5′–> 3′ direction and other in 3’—> 5’direction. , The backbone of DNA is formed by the sugar phosphate-sugar chain. The nitrogen bases are projected more or less perpendicular to the backbone of DNA and faces inside. A and G of one strand base pairs with T and C respectively on the other strand. Between A and T (A== T), there are two hydrogen bonds while, there are three hydrogen bonds between G and C(G=C). DNA has a uniform thickness of 20 A and pitch of is 34 nm. Thus, one turn of DNA measures 3.4 nm (rise per base pair) and consists of 10 nucleotides (or ten base pairs). This form of DNA is called B-DNA. Functions of Nucleic Acids Nucleic acid plays multiple role in living organism these are given as follows (i) It enables cell to grow, maintain and divide by directing the synthesis of structural proteins. (ii) Acts as a genetic material, i.e., transfer hereditary characters from one generation to the next. Differences between DNA and RNA are given below 1. Peptide Bond In a polypeptide or a protein, amino acids are linked by a peptide bond. Formed when the carboxyl group (—COOH) of one amino acid reacts with the amino group (—NH2) of the next amino acid with elimination of water. 2. Glycosidic Bond It is formed between two carbon atoms of two adjacent monosaccharides, thus it forms a polysaccharide by linking individual monosaccharides. This bond is also formed by dehydration (removal of water). 3. Phosphodiester Bond In a nucleic acid a phosphate moiety links the 3,carbon of one sugar of one nucleotide to the 5’carbon of the sugar of the succeeding nucleotide. The bond between the phosphate and hydroxyl group of sugar is an ester b id. As there is one such ester bond on either side, it is called phosphodiester bond. Dynamic State of Body Constituents Nature of Bond Linking Monomers in a Polymer The polymers described above in the topic are formed by the combination or linking of one or more type of monomer units. So, in order to link these units together various types of bonds are required depending on the nature and the type of macromolecule. Concept of Metabolism Each cell contain thousands of organic compounds. These compounds or biomolecules are present in living organisms in various concentrations. Turn over of biomolecules is one of the greatest discoveries. It is the phenomenon in which biomolecules change constantly into some other biomolecules or made from some other biomolecules. All these, transfer of one biomolecule into other occur due to chemical reaction which continuously take place in an organism. The chemical reactions together are called metabolism. Each metabolic reaction results in the process of transformation, e.g., an amino acid when transforms into an amine, C02 is removed, removal of amino group in a nucleotide base, etc. Majority of these metabolic reactions do not occur in isolation, instead they take place in a series of linked reaction known as metabolic pathways. These pathways are either linear or circular and criss-cross each other, i.e., there are traffic functions. Flow of metabolites through metabolic pathway has a definite rate and direction and this metabolic flow is called the dynamic state of body constituents. Also these metabolic reactions are always catalyzed reaction, i.e., no uncatalysed metabolic conversion is present in living systems. The catalysts which hasten the rate of a given metabolic conversion are also proteins. These proteins with catalytic power are called enzymes. Metabolic Basis for Living Metabolic pathways in living organisms are divided into two main types i. Anabolic Pathways These include the formation of complex structure from simple ones, e.g., formation of cholesterol from acetic acid, protein synthesis, etc. These are energy consuming pathways. ii. Catabolic Pathways Glycolysis Glucose is degraded to lactic acid in human skeletal muscle, liberating energy. This metabolic pathway from glucose to lactic acid which occurs in ten metabolic steps is called glycolysis. This liberated energy is stored in the form of chemical bonds and this bond energy can be utilised in various biosynthetic, osmotic and mechanical work when needed. Adenosine Triphosphate (ATP) The most important form of energy currency present in living systems is the bond energy in a chemical compound of ATP. The Living State Various chemical compounds (metabolites or biomolecules) are present at a concentration characteristic of each of them, i.e., all living organisms exist in a steady state characterized by concentrations of each of these biomolecules. It is the most important fact of biological systems. These metabolites are in a state of metabolic flux. Hence, the living system is kept in a non-equilibrium state by metabolic flux, which enables it to perform work as living organism. It has to work continuously and are unable to reach equilibrium. Therefore, metabolism is helpful in providing a mechanism which enables energy production. It can be stated that the living state and . metabolism are synonymous and are correlated. Thus, metabolism and living state are incomplete without each other. These include the formation of simpler structures, i.e., the breakage of complex structures into simpler ones, e.g., Conversion of glucose into lactic acid in skeletal muscles. These are energy releasing

CLASS 11 CHAPTER-10 CELL DIVISION AND CELL CYCLE
https://acrobat.adobe.com/id/urn:aaid:sc:EU:b4460390-2136-4b26-9ec6-6be7c5d63eac CLASS 11 CHAPTER-10 CELL DIVISION AND CELL CYCLE CELL DIVISON: It is the process by which a mature cell divides and forms two nearly equal daughter cells which resemble the parental cell in a number of characters. Discovery: 1. Prevost and Dumas (1824) first to study cell division during the cleavage of zygote of frog. 2. Nagelli (1846) was the first to propose that new cells are formed by the division of pre-existing cells. 3. Rudolf Virchow (1859) proposed “omnis cellula e cellula” and “cell lineage theory”. 4. A cell divides when it has grown to a certain maximum size which disturb the karyoplasmic index (KI)/Nucleoplasmic ratio (NP)/Kernplasm connection. Two processes take place during cell reproduction. ⚫ Cell growth: (Period of synthesis and duplication of various components of cell). ⚫ Cell division: (Mature cell divides into two cells). CELL CYCLE: Howard and Pelc (1953) first time described it. The sequence of events which occur during cell growth and cell division are collectively called cell cycle. Cell cycle completes in two steps: (i) Interphase: It is the period between the end of one cell division to the beginning of next cell division. It is also called resting phase or not dividing phase. But, it is actually highly metabolic active phase, in which cell prepares itself for next cell division. In case of human beings it will take approx 25 hours. Interphase is completed in to three successive stages. (a) G1 phase/Post mitotic/Pre-DNA synthetic phase/Gap Ist (b) S-phase/Synthetic phase (c) G2-phase/Pre mitotic/Post synthetic phase/gap-IInd (ii) M-phase/Dividing phase/Mitotic phase (a) Nuclear division i.e. karyokinesis occurs in 4 phases – prophase, metaphase, anaphase and telophase. It takes 5-10% (shortest phase) time of whole division. (b) Cytokinesis : Division of cytoplasm into 2 equal parts. In animal cell, it takes place by cell furrow method and in plant cells by cell plate method. 1. Duration of cell cycle: It depends on the type of cell and external factors such as temperature, food and oxygen. Time period for G1, S, G2 and M-phase is species specific under specific environmental conditions. e.g. 20 minutes for bacterial cell, 8-10 hours for intestinal epithelial cell, and onion root tip cells may take 20 hours. Regulation of cell cycle: Stage of regulation of cell cycle is G1 phase during which a cell may follow one of the three options: ⚫ It may start a new cycle, enter the S-phase and finally divide. ⚫ It may be arrested at a specific point of G1 phase. ⚫ It may stop division and enter G0 quiscent stage. But when conditions change, cell in G0 phase can resume the growth and reenter the G1 phase. The cell cycle may also be regulated by some biochemical switches which control the transition from one phase to another. These regulatory molecules are of two types - • Cyclins - act as regulatory subunit which are formed in the cell when it gets a signal to divide. • Cyclin Dependent Kinases (CDKs) - are catalytic subunit which are present in the cell in inactive forms. They are activated when cyclin bind to them. Together the cyclin and CDKs trigger the phosphorylation of proteins which push the cell to move from one phase to another. Cell division is of three types, Amitosis, Mitosis and Meiosis. DIFFERENCE BETWEEN CELL MITOSIS AND MEIOSIS S.No Characters Mitosis Meiosis I. General (1) Site of occurrence Somatic cells and during the multiplicative phase of gametogenesis in germ cells. Reproductive germ cells of gonads. (2) Period of occurrence Throughout life. During sexual reproduction. (3) Nature of cells Haploid or diploid. Always diploid. (4) Number of divisions Parental cell divides once. Parent cell divides twice. (5) Number of daughter cells Two. Four. (6) Nature of daughter cells Genetically similar to parental cell. Amount of DNA and chromosome number is same as in parental cell. Genetically different from parental cell. Amount of DNA and chromosome number is half to that of parent cell. II. Prophase (7) Duration Shorter (of a few hours) and simple. Prophase-I is very long (may be in days or months or years) and complex. (8) Subphases Formed of 3 subphases : earlyprophase, mid-prophase and lateprophase. Prophase-I is formed of 5 subphases: leptotene, zygotene, pachytene, diplotene and diakinesis. (9) Bouquet stage Absent. Present in leptotene stage. (10) Synapsis Absent. Pairing of homologous chromosomes in zygotene stage. (11) Chiasma formation and crossing over. Absent. Occurs during pachytene stage of prophase-I. (12) Disappearance of nucleolus and nuclear membrane Comparatively in earlier part. Comparatively in later part of prophase-I. (13) Nature of coiling Plectonemic. Paranemic. III. Metaphase (14) Metaphase plates Only one equatorial plate Two plates in metaphase-I but one plate in metaphase-II. (15) Position of centromeres Lie at the equator. Arms are generally directed towards the poles. Lie equidistant from equator and towards poles in metaphase-I while lie at the equator in metaphase-II. (16) Number of chromosomal fibres Two chromosomal fibre join at centromere. Single in metaphase-I while two in metaphase-II. IV. Anaphase (17) Nature of separating chromosomes Daughter chromosomes (chromatids with independent centromeres) Homologous chromosomes separate in anaphase-I while chromatids separate. separate in anaphase in anaphase-II. (18) Splitting of centromeres and development of inter-zonal fibers Occurs in anaphase. No splitting of centromeres. Interzonal fibres are developed in metaphase-I. V. Telophase (19) Occurrence Always occurs Telophase-I may be absent but telophase-II is always present. VI. Cytokinesis (20) Occurrence Always occurs Cytokinesis-I may be absent but cytokinesis-II is always present. (21) Nature of daughter cells 2N amount of DNA than 4N amount of DNA in parental cell. 1 N amount of DNA than 4 N amount of DNA in parental cell. (22) Fate of daughter cells Divide again after interphase. Do not divide and act as gametes. VII. Significance (23) Functions Helps in growth, healing, repair and multiplication of somatic cells. Occurs in both asexually and sexually reproducing organisms. Produces gametes which help in sexual reproduction. (24) Variations Variations are not produced as it keeps quality and quantity of genes same. Produces variations due to crossing over and chance arrangement of bivalents at metaphase-I. (25) In evolution No role in evolution. It plays an important role in speciation and evolution. Figure: Difference between mitosis and meiosis PRACTICE PROBLEMS Q1. A cell has 12 chromosomes in its nucleus. What will be the number of chromosomes in the cell after DNA replication at the end of S phase? (a) 24 (b) 12 (c) 6 (d) 36 Solution: During the S phase of the cell cycle the DNA replicates and doubles itself. However the chromatin fibers in the nucleus of the cell do not duplicate and hence even though the cell has double the amount of DNA, the number of chromosomes in the nucleus remains the same. Thus the cell will have 12 chromosomes at the end of S phase. Hence, the correct option is (b). Q2. Duplication of mitochondria and chloroplasts occurs during which phase of the cell cycle? (a) G1 phase (b) G2 phase (c) S phase (d) both (a) and (b) Solution: Both G1 and G2 phases involve the synthesis of RNA and proteins and division and duplication of cell organelles such as mitochondria and chloroplasts. S phase is involved only with the replication of DNA. Thus, the correct option is (d). Q3. Which of these is the most eventful period of the cell cycle? (a) G1 phase (b) G2 phase (c) S phase (d) M phase Solution: Most of the visible events and changes in the cell take place during M phase. In spite of being the shortest phase of the cell, the cell undergoes maximum amount of change in its nucleus and cytoplasm during this phase. The M phase is further divided into karyokinesis (division of nucleus) and cytokinesis (division of cytoplasm). The karyokinesis involves four phases - prophase, metaphase, anaphase and telophase, during which the chromosomes duplicate themselves, divide to form daughter chromosomes and get distributes into the two daughter nuclei that are formed. Thus, the correct answer is option (d). Q4. Find out the correct statement: (a) A somatic cell that has just completed the S phase of its cell cycle has twice the number of chromosomes and twice the amount of DNA compared to a gamete of the same species. (b) A somatic cell that has just completed the S phase of its cell cycle has the same number of chromosomes but twice the amount of DNA compared to a gamete of the same species. (c) A somatic cell that has just completed the S phase of its cell cycle has twice the number of chromosomes and four times the amount of DNA compared to a gamete of the same species. (d) A somatic cell that has just completed the S phase of its cell cycle has four times the number of chromosomes and twice the amount of DNA compared to a gamete of the same species. Solution: Suppose, a somatic cell has 2n number of chromosomes in its normal diploid condition and the amount of DNA in the cell is C. A gamete of the same species will have n number of chromosomes and ½ C amount of DNA. At the end of S phase, the somatic cell will have double the amount of DNA, that is, 2C but the number of chromosomes will be the same. Thus, at this point, the cell has four times the amount of DNA and double the number of chromosomes compared to a gamete of the same species. Thus, the correct option is (c). FAQs Question 1. Being the resting phase, is interphase a metabolically inactive phase? Answer: The interphase is wrongly called as the resting phase as this phase is metabolically highly active and actively synthesizes DNA, RNA, proteins, ATP and all that it would need for cell division. Question 2. What is cell cycle arrest? Answer: Cell cycle arrest refers to the stopping of the cell cycle at one of the checkpoints. Cell cycle arrest can be triggered by lack of nutrients, DNA damage, certain chemicals, etc. Question 3. What does cell cycle arrest at the G2/M phase indicate? Answer: If the cell cycle is arrested at the G2/M phase checkpoint, then it indicates that the cell has some errors in DNA replication or DNA damage. At this point, the cell either tries to repair the damage or undergoes a programmed cell death if the damage is irreparable. Question 4. How do cells die? Answer: Cells can die in four different ways - • Apoptosis or programmed cell death is activated due to the release of certain chemicals known as caspases which destroy the cell from within and the cell contents are not released outside. Thus, it does not trigger the immune system. • Necrosis is the death of the cell due to release of toxins or lack of blood supply. Cell contents are released into the blood stream and the immune system is triggered. • Necroptosis is a programmed cell death triggered by certain proteins but the cell contents may leak out. • Pyroptosis is the highly inflammatory death of virus or bacteria infected cells due to release of cytokines.

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