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CLASS 9 | SCIENCE (বিজ্ঞান) | ASSEB

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Class 9 Science Video Lectures by Ridib Sir

  • Class 9 Science – Introduction to Science
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  • Class 9 science – States of Matter আমাৰ চাৰিওকাষৰ বস্তুবোৰ Part 1
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  • Class 9 Science – States of Matter আমাৰ চাৰিওকাষৰ বস্তুবোৰ Part 2
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  • Chapter 2 – Is matter around us pure আমাৰ চৌপাশৰ বস্তুবোৰ বিশুদ্ধনে ?
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  • Chapter 2 – Is Matter around us Pure আমাৰ চৌপাশৰ বস্তুবোৰ বিশুদ্ধনে? Part 2
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  • Chapter 3 – Atoms and Molecules অণু আৰু পৰমাণু
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  • Chapter 4 – Structure of Atom পৰমাণুৰ গঠন (Lecture 1)
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  • Chapter 4- Structure of atom পৰমাণুৰ গঠন (Lecture 2)
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  • Chapter 4 – Structure of Atom পৰমাণুৰ গঠন (Lecture 3)
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  • Chapter 4 – Structure of Atoms, পৰমাণুৰ গঠন (Lecture 4)
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  • Chapter 5 – The fundamental unit of Life জীৱৰ মৌলিক একক Lecture 1
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  • Chapter 5 – The fundamental unit of life জীৱৰ মৌলিক একক Lecture 2
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  • Chapter 5- The fundamental unit of life জীৱৰ মৌলিক একক Lecture 3
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  • Chapter 5- The fundamental unit of life জীৱৰ মৌলিক একক Lecture 4
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  • Chapter 5-The fundamental unit of life জীৱৰ মৌলিক একক Lecture 5
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  • Chapter 6 – Tissues কলা Lecture 1
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  • Chapter 6 – Tissues কলা Lecture 2
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  • Chapter 6 – Tissues কলা Lecture 3
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  • Chapter 6 – Tissues কলা Lecture 4
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  • Chapter 6 – Tissues কলা Lecture 5
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  • Chp- 7 : Diversity in living organisms জীৱৰ বিচিত্ৰতা part 1
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  • Chp- 7 : Diversity in living organisms জীৱৰ বিচিত্ৰতা part 2
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  • Chp- 7 : Diversity in living organisms জীৱৰ বিচিত্ৰতা part 3
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  • Chapter 8 – Motion গতি Lecture 1
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  • Chapter 8 – Motion গতি Lecture 2
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  • Chapter 8 – Motion গতি Lecture 3
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  • Chapter 8 – Motion গতি Lecture 4
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  • Chapter 8 – Motion গতি lecture 5
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  • Chapter 9 – Force and Laws of Motion বল আৰু গতি বিষয়ক সুত্ৰসমূহ (part 1)
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  • Chapter 9 – Force and Laws of Motion বল আৰু গতি বিষয়ক সুত্ৰসমূহ ( part 2)
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  • Chapter 10 – Gravitation (মহাকৰ্ষণ) Lecture 1
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  • Chapter 10 – Gravitation (মহাকৰ্ষণ) Lecture 2
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  • Chapter 10 -Gravitation (মহাকৰ্ষণ) Lecture 3
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  • Chapter 10 – Gravitation (মহাকৰ্ষণ) – Exercises and Revision by Ridib Sir
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  • Chapter 10 – Gravitation(মহাকৰ্ষণ)- Exercises and Revision by Ridib Sir part 2
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  • Chapter 11 – Work and Energy (কাৰ্য আৰু শক্তি) Lecture 1
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  • Chapter 11 – Work & Energy (কাৰ্য আৰু শক্তি) lecture 2
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  • Chapter 11 – Work and Energy (কাৰ্য আৰু শক্তি) Lecture 3
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  • Chapter 11 – Work, energy and Power (কাৰ্য আৰু শক্তি) (Q&A )
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  • Chapter 14 Natural Resources (প্ৰাকৃতিক সম্পদ) 1
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  • Chapter 14- Natural Resources (প্ৰাকৃতিক সম্পদ) 2
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  • Chapter 15 – Improvement in Food Resources (খাদ্য সম্পদৰ উতকৰ্ষ সাধন) 1
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  • Chapter 15 – Improvement in Food Resources (খাদ্য সম্পদৰ উতকৰ্ষ সাধন) 2
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  • Chapter 15 – Improvement in Food Resources (খাদ্য সম্পদৰ উতকৰ্ষ সাধন) 3
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  • Chapter 15 – Improvement in Food Resources (খাদ্য সম্পদৰ উতকৰ্ষ সাধন) 4
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  • Chapter 15 – Improvement in Food Resources (খাদ্য সম্পদৰ উতকৰ্ষ সাধন) 5
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  • Chapter 15 – Improvement in Food Resources (খাদ্য সম্পদৰ উতকৰ্ষ সাধন) 6
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  • Chapter 15 – Improvement in Food Resources (খাদ্য সম্পদৰ উতকৰ্ষ সাধন) 7
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Questions and Answers on Class 9 Chapter on – Is Matter Around Us Pure

Class 9 Video Lectures by Sneha Madam

Revision Class Video Lectures

Exam notes on NCERT Class 9 chapter – Unit I: Matter-Nature and Behaviour

Exam Notes on Motion, Force and Work

Exam notes on Class 9 Science Chapter on Structure of Atom
Exam notes on NCERT Class 9 Science Chapter - "Structure of Atom": **Chapter Overview:** "Structure of Atom" in Class 9 Science explores the structure of atoms, including the subatomic particles within atoms, the arrangement of electrons in energy levels, and the atomic model proposed by various scientists. **Key Concepts:** 1. **Subatomic Particles:** - Atoms are composed of three subatomic particles: protons, neutrons, and electrons. - Protons carry a positive charge, neutrons are neutral, and electrons carry a negative charge. 2. **Electron Distribution:** - Electrons are arranged in energy levels or shells around the nucleus. - The first energy level can hold a maximum of 2 electrons, the second level can hold up to 8, and the third level can hold up to 18. 3. **Valency:** - Valency is the combining capacity of an element, which depends on the number of electrons in its outermost shell. - Elements tend to gain, lose, or share electrons to achieve a stable electron configuration. 4. **Atomic Number:** - Atomic number represents the number of protons in an atom's nucleus. - It defines the identity of an element and its position in the periodic table. 5. **Isotopes:** - Isotopes are atoms of the same element with the same atomic number but different mass numbers due to varying numbers of neutrons. 6. **Bohr's Atomic Model:** - Niels Bohr proposed an atomic model where electrons move in fixed orbits around the nucleus. - Electrons can jump between energy levels by absorbing or emitting energy. 7. **Rutherford's Atomic Model:** - Ernest Rutherford's experiments led to the discovery of the atomic nucleus, which is dense and positively charged. - Electrons move in the space around the nucleus. 8. **Thomson's Atomic Model:** - J.J. Thomson proposed the "plum pudding" model, where electrons are embedded in a positively charged sphere. **Practical Applications:** - Understanding the structure of atoms is fundamental to chemistry, as it explains how atoms combine to form compounds and participate in chemical reactions. **Conclusion:** This chapter provides students with a foundational understanding of the structure of atoms, the arrangement of subatomic particles within atoms, and the models proposed by scientists to describe atomic structure. It forms the basis for further exploration of chemistry and the behavior of elements and compounds.

Questions and Answers on Class 9 Science Chapter on Structure of Atom
### Questions and Answers on NCERT Class 9 Science: Structure of Atom #### 1. Question: What are the three subatomic particles of an atom? - **Answer**: The three subatomic particles of an atom are protons, neutrons, and electrons. #### 2. Question: Who discovered the electron? - **Answer**: The electron was discovered by J.J. Thomson in 1897. #### 3. Question: Describe Rutherford's model of the atom. - **Answer**: Rutherford's model of the atom, proposed by Ernest Rutherford, suggested that an atom consists of a tiny, dense, positively charged core called the nucleus, around which electrons revolve in circular orbits. The model is often compared to a mini solar system where electrons orbit the nucleus like planets orbit the sun. #### 4. Question: What is the charge and mass of an electron? - **Answer**: An electron has a negative charge, denoted as ‘e-’. The charge of an electron is (1.6 times 10^{-19} C) and its mass is (9.1 times 10^{-31} kg). #### 5. Question: What are isotopes? - **Answer**: Isotopes are atoms of the same element that have the same number of protons (and hence the same atomic number) but different numbers of neutrons, resulting in different atomic masses. #### 6. Question: Define atomic number and mass number. - **Answer**: - **Atomic Number (Z)**: The number of protons present in the nucleus of an atom. - **Mass Number (A)**: The total number of protons and neutrons present in the nucleus of an atom. #### 7. Question: Explain the Bohr’s model of the atom. - **Answer**: Bohr's model of the atom suggests that electrons revolve in stable, well-defined orbits around the nucleus without radiating energy. Electrons occupy energy levels or shells, and the energy of an electron is quantized, meaning it can only take on certain specific values. #### 8. Question: What are valence electrons? - **Answer**: Valence electrons are the electrons present in the outermost shell of an atom. These electrons are involved in the formation of chemical bonds with other atoms. #### 9. Question: Define the term “electron configuration”. - **Answer**: Electron configuration refers to the arrangement of electrons in different shells around the nucleus of an atom. It is denoted by numbers and letters where numbers represent the shell and letters (s, p, d, f) represent subshells. #### 10. Question: Describe the distribution of electrons in shells. - **Answer**: The distribution of electrons in shells follows the 2n^2 rule, where 'n' is the shell number. The maximum number of electrons that can be accommodated in a shell is given by 2n^2. - K shell (n=1) = 2 electrons - L shell (n=2) = 8 electrons - M shell (n=3) = 18 electrons, and so on. #### 11. Question: What is the significance of valency in the formation of a molecule? - **Answer**: Valency indicates the combining capacity of an atom to form bonds and become stable. Atoms bond with each other by either transferring or sharing valence electrons to attain a stable electronic configuration (often akin to the nearest noble gas). Therefore, valency plays a crucial role in determining how and with what atoms will combine to form molecules. #### 12. Question: Who proposed the electron cloud model of atom? - **Answer**: The electron cloud model, or the quantum mechanical model of the atom, was developed primarily by Erwin Schrödinger and Werner Heisenberg in the 1920s. Note: It’s essential to refer back to your NCERT Class 9 Science textbook for detailed study and accurate information, as it is the primary source for exam preparation. Ensure to correlate these answers with your text and understand the concepts thoroughly for effective learning and preparation for your exams.

Exam notes on NCERT Class 9 Science Chapter on Basic Unit Of Life
Exam notes on NCERT Class 9 Science Chapter - "The Fundamental Unit of Life": **Chapter Overview:** "The Fundamental Unit of Life" in Class 9 Science focuses on the basic unit of living organisms, which is the cell. The chapter explores the structure and functions of cells, their types, and their significance in living organisms. **Key Concepts:** 1. **Cell:** - The cell is the basic structural and functional unit of all living organisms. - It is the smallest entity that can perform all life processes. 2. **Cell Theory:** - The cell theory states that all living organisms are composed of cells, and the cell is the basic unit of life. 3. **Types of Cells:** - Cells can be categorized into two types: prokaryotic cells (lacking a nucleus) and eukaryotic cells (containing a nucleus). 4. **Cell Structure:** - A typical eukaryotic cell consists of a cell membrane, cytoplasm, nucleus, and various organelles. 5. **Cell Membrane:** - The cell membrane or plasma membrane surrounds the cell and regulates the entry and exit of substances. 6. **Cytoplasm:** - The cytoplasm is a gel-like substance that contains various organelles and is the site of many cellular processes. 7. **Nucleus:** - The nucleus is the control center of the cell and contains genetic material (DNA) that governs cell activities. 8. **Organelles:** - Organelles are specialized structures within the cell that perform specific functions. - Examples include mitochondria (energy production), endoplasmic reticulum (protein synthesis), and Golgi apparatus (packaging and transport). 9. **Chloroplasts (in Plant Cells):** - Chloroplasts are organelles in plant cells responsible for photosynthesis, where sunlight is converted into energy. 10. **Vacuoles (in Plant Cells):** - Vacuoles store water, nutrients, and waste products in plant cells. **Practical Applications:** - Understanding the structure and functions of cells is crucial for biology and the study of living organisms. It provides insights into how cells function, reproduce, and contribute to the overall functioning of organisms. **Conclusion:** This chapter introduces students to the concept of cells as the fundamental unit of life. It covers the structure and functions of cells, the differences between prokaryotic and eukaryotic cells, and the various organelles that play essential roles in cell processes. This foundational knowledge is critical for further studies in biology and life sciences.

Questions and Answers on NCERT Class 9 Science Chapter on Basic Unit Of Life
### Questions and Answers on NCERT Class 9 Science: Basic Unit Of Life #### 1. Question: What is a cell? - **Answer**: A cell is the basic structural and functional unit of life. All living organisms are made up of cells, which can function independently or as a part of multicellular organisms. #### 2. Question: Differentiate between Prokaryotic and Eukaryotic cells. - **Answer**: - **Prokaryotic cells**: Lack a well-defined nucleus and membrane-bound organelles (e.g., bacteria). - **Eukaryotic cells**: Possess a well-defined nucleus and have membrane-bound organelles (e.g., plants, animals, fungi). #### 3. Question: What is the function of the plasma membrane? - **Answer**: The plasma membrane, or cell membrane, regulates the movement of substances in and out of the cell, thus maintaining the internal environment. It protects the cell and provides a boundary, while its selective permeability allows specific substances to pass through. #### 4. Question: Describe the structure of a nucleus. - **Answer**: The nucleus is a spherical structure enclosed by a double-membraned nuclear envelope, which has pores for substance exchange. Inside, it contains chromatin, which consists of DNA and proteins, and a nucleolus, which is involved in ribosome synthesis. #### 5. Question: Explain the role of mitochondria. - **Answer**: Mitochondria are often termed the "powerhouse of the cell" because they generate ATP, which is the energy currency used by the cell. They also play a role in processes like cell death, cell division, and cell growth. #### 6. Question: What is osmosis? - **Answer**: Osmosis is the movement of water molecules from a region of lower solute concentration to a region of higher solute concentration through a semi-permeable membrane. #### 7. Question: Describe the function of the vacuole. - **Answer**: Vacuoles are storage sacs found within cells. In plant cells, a central vacuole stores nutrients, wastes, and helps maintain turgor pressure. In animal cells, smaller vacuoles may store water, ions, or waste materials. #### 8. Question: What is the role of lysosomes? - **Answer**: Lysosomes, often referred to as "suicide bags," contain digestive enzymes and play a crucial role in breaking down cellular waste and foreign invaders like bacteria, thereby cleaning the cell. They can also induce cell death when required. #### 9. Question: Differentiate between plant cells and animal cells. - **Answer**: - **Plant Cells**: Have a cell wall, contain a large central vacuole, and possess chloroplasts for photosynthesis. - **Animal Cells**: Lack a cell wall and chloroplasts, have smaller and numerous vacuoles, and contain centrioles. #### 10. Question: What is cytoplasm? - **Answer**: Cytoplasm is the jelly-like substance inside the cell, enclosed by the cell membrane. It contains organelles and is the site where most cellular activities occur, such as respiration, protein synthesis, and nutrient processing. #### 11. Question: Explain the function of the endoplasmic reticulum. - **Answer**: The endoplasmic reticulum (ER) is an organelle that plays a crucial role in synthesizing and transporting proteins and lipids. The rough ER, studded with ribosomes, is involved in protein synthesis, while the smooth ER is involved in lipid synthesis and detoxification processes. #### 12. Question: Describe the role of ribosomes in a cell. - **Answer**: Ribosomes are involved in synthesizing proteins by translating the genetic instructions (mRNA) into amino acid sequences. They can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum. #### Note: Remember to refer back to your NCERT Class 9 Science textbook for detailed answers and revisit the concepts to prepare effectively for your exams. It’s crucial to understand the theory and mechanisms to be able to answer the questions accurately.

Exam notes on NCERT Class 9 Science Chapter on Tissues, Organs, Organ Systems and Organisms
Exam notes on NCERT Class 9 Science Chapter - "Tissues, Organs, Organ Systems, and Organisms": **Chapter Overview:** In Class 9 Science, the chapter "Tissues, Organs, Organ Systems, and Organisms" explores the hierarchical organization of living organisms, from cells to tissues, organs, organ systems, and the entire organism. It delves into the functions and coordination of these levels of organization. **Key Concepts:** 1. **Levels of Organization:** - Living organisms are organized into various levels: cells, tissues, organs, organ systems, and organisms. 2. **Cells:** - Cells are the basic structural and functional units of living organisms. - Cells with similar functions and structures group together to form tissues. 3. **Tissues:** - Tissues are groups of cells that work together to perform specific functions. - Four main types of tissues in animals are epithelial, connective, muscular, and nervous. 4. **Organs:** - Organs are composed of two or more types of tissues that work together to perform a particular function. - Examples of organs include the heart, lungs, liver, and brain. 5. **Organ Systems:** - Organ systems are groups of organs that work together to perform complex functions. - The human body has several organ systems, such as the circulatory system, respiratory system, and digestive system. 6. **Coordination and Integration:** - The various organ systems in an organism coordinate and integrate their functions to maintain homeostasis. - Homeostasis refers to the body's ability to maintain a stable internal environment despite external changes. 7. **Functioning of Organ Systems:** - Each organ system has a specific function and contributes to the overall functioning of the organism. - For example, the digestive system is responsible for breaking down and absorbing nutrients, while the respiratory system is involved in oxygen exchange. **Practical Applications:** - Understanding the hierarchical organization of living organisms and the coordination among different levels of organization is essential for the study of biology and human physiology. **Conclusion:** This chapter provides students with a comprehensive understanding of how living organisms are organized into cells, tissues, organs, and organ systems. It emphasizes the importance of coordination and integration among these levels to maintain the body's functions. This knowledge forms the foundation for the study of anatomy, physiology, and biology.

Questions and Answers on NCERT Class 9 Science Chapter on Tissues, Organs, Organ Systems and Organisms
Questions and answers related to NCERT Class 9 Science Chapter concerning Tissues, Organs, Organ Systems, and Organisms. Note that this is not an exhaustive list and it's always a good idea to refer to the NCERT textbook for comprehensive study material. ### Questions and Answers: #### Q1: What is a tissue? **A1**: A tissue is a group of similar cells that work together to perform a particular function. It can have more than one type of cell. #### Q2: Differentiate between a plant cell and an animal cell. **A2**: Plant cells typically have a cell wall, a large central vacuole, and plastids, which are not found in animal cells. Animal cells generally have a round shape while plant cells are more likely to be rectangular or cubic in shape. #### Q3: Explain the concept of an organ system. **A3**: An organ system is a group of organs that work together to perform a major function. For instance, the digestive system, which includes organs like the stomach, liver, and intestines, works together to break down food, absorb nutrients, and remove waste. #### Q4: Define the term “organ” and provide two examples. **A4**: An organ is a structured group of tissues that perform a specific function in an organism. Examples include the heart, which pumps blood throughout the body, and the lungs, which enable breathing and gas exchange. #### Q5: What is the role of the nervous tissue? **A5**: Nervous tissue is specialized for transmitting electrical impulses. It allows for coordination and control in the body by transmitting signals between different parts of the organism, thus helping in responding to various stimuli. #### Q6: What are meristematic tissues in plants? **A6**: Meristematic tissues in plants are responsible for growth. The cells in these tissues are capable of dividing and contributing to the increase in length and thickness of the plant. They are usually found in regions like the tips of stems and roots. #### Q7: How do organisms maintain homeostasis? **A7**: Organisms maintain homeostasis, or stable internal conditions, through various organ systems and regulatory mechanisms that control factors like temperature, pH, and the concentration of ions in their bodily fluids. They respond to external and internal stimuli to keep conditions within permissible limits. #### Q8: Define the term "organism" and provide an example. **A8**: An organism is a living entity composed of one or more cells that exhibit all the characteristics of life, such as growth, movement, response to stimuli, and reproduction. Examples of organisms include bacteria, plants, animals, and fungi. #### Q9: What is the significance of epithelial tissue in animals? **A9**: Epithelial tissue acts as a protective barrier that covers both the external and internal surfaces of the body, including organs and vessels. It protects against physical injury, bacteria, and drying out. Additionally, it is involved in functions like secretion, absorption, and sensation. #### Q10: Why are xylem and phloem important for plants? **A10**: Xylem and phloem are crucial vascular tissues in plants. Xylem helps in transporting water and minerals from the roots to other parts of the plant, whereas phloem transports food, primarily in the form of sucrose, from leaves (where it’s synthesized during photosynthesis) to other parts. Remember to refer to the NCERT Class 9 Science textbook for detailed explanations and additional questions related to tissues, organs, organ systems, and organisms. Practice is key in science, so try to understand the concepts and then attempt various questions for revision!

Exam notes on Class 9 Science Chapter on Force and Newton’s Law of motion
Exam notes on NCERT Class 9 Science Chapter - "Force and Newton's Laws of Motion": **Chapter Overview:** "Force and Newton's Laws of Motion" in Class 9 Science introduces students to the fundamental concepts of force, its effects on motion, and Sir Isaac Newton's three laws of motion. **Key Concepts:** 1. **Force:** - Force is a push or pull acting on an object. It can change the object's state of rest or motion. 2. **Contact and Non-contact Forces:** - Contact forces require physical contact between objects (e.g., friction, tension). - Non-contact forces act at a distance (e.g., gravitational force, magnetic force). 3. **Balanced and Unbalanced Forces:** - Balanced forces do not change an object's motion; the object remains at rest or moves with a constant velocity. - Unbalanced forces cause acceleration, leading to a change in motion. 4. **Newton's First Law of Motion (Law of Inertia):** - An object at rest tends to stay at rest, and an object in motion tends to stay in motion with the same speed and direction unless acted upon by an unbalanced force. 5. **Newton's Second Law of Motion:** - The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. - F = ma, where F is force, m is mass, and a is acceleration. 6. **Newton's Third Law of Motion:** - For every action, there is an equal and opposite reaction. When one object exerts a force on another, the second object exerts an equal and opposite force on the first. 7. **Momentum:** - Momentum is the product of an object's mass and velocity. - Momentum = mass × velocity **Practical Applications:** - Understanding force and Newton's laws of motion is crucial for various real-world applications, including engineering, transportation, and sports. **Conclusion:** This chapter introduces students to the concept of force, the effects of balanced and unbalanced forces, and the three laws of motion formulated by Sir Isaac Newton. It provides a foundation for understanding the principles governing the motion of objects and their interactions with forces.

Questions and Answers on NCERT Class 9 Science Chapter on Force and Newton’s Law
Possible questions and answers related to the NCERT Class 9 Science Chapter concerning Force and Newton's Laws of Motion. ### Questions and Answers: #### Q1: Define Force. **A1**: Force is a push or pull on an object that can cause it to change its state of motion or shape. It has both magnitude and direction, making it a vector quantity. #### Q2: State Newton’s First Law of Motion. **A2**: Newton's First Law of Motion states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external unbalanced force. #### Q3: What is inertia? **A3**: Inertia is the inherent property of a body that resists changes in its state of motion. A body at rest wants to stay at rest, and a body in motion wants to stay in motion unless an external force acts on it. #### Q4: Explain Newton’s Second Law of Motion. **A4**: Newton's Second Law of Motion states that the rate of change of momentum of an object is directly proportional to the applied unbalanced force and takes place in the direction in which the force acts. Mathematically, F = ma, where F is the force, m is the mass, and a is the acceleration. #### Q5: Why does a heavy truck and a cycle require different amounts of force to move? **A5**: According to Newton's Second Law of Motion, the force required to move an object is directly proportional to its mass (F = ma). A heavy truck has much more mass than a cycle, so it requires more force to accelerate it. #### Q6: Describe Newton’s Third Law of Motion. **A6**: Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. It means that if body A exerts a force on body B, then body B simultaneously exerts an equal and opposite force on body A. #### Q7: Why is it easier to stop a rolling ball than a moving bicycle? **A7**: It's easier to stop a rolling ball than a moving bicycle because of the difference in their masses. The bicycle has more mass than the ball, and according to Newton's Second Law of Motion, a body with more mass requires a greater force to change its state of motion than a body with less mass. #### Q8: What is meant by "reaction time"? **A8**: Reaction time refers to the interval between the receipt of the signal to stop and the actual act of stopping. It is the time taken by a person to respond to a particular situation or stimulus, and it may depend on the individual’s alertness and physical fitness. #### Q9: What is momentum? **A9**: Momentum is the product of the mass and velocity of an object. It is a vector quantity and has the same direction as the velocity. Mathematically, momentum (p) is given by p = mv, where m is the mass and v is the velocity. #### Q10: How does a karate player break a slab with a blow? **A10**: A karate player breaks a slab by applying a force in a very short interval of time, which increases the rate of change of momentum and thus applies a large force to the slab according to Newton’s Second Law of Motion. This large force is sufficient to overcome the cohesive forces between the particles of the slab, causing it to break. These questions and answers offer a fundamental overview of the chapter on Force and Newton's Law in Class 9 Science. It’s beneficial to work through various other problems and conceptual questions in your NCERT textbook to get a solid understanding of the chapter.

Exam notes on NCERT Class 9 Science Chapter on Gravitation
Some exam notes on NCERT Class 9 Science Chapter - "Gravitation": **Chapter Overview:** "Gravitation" in Class 9 Science explores the fundamental concept of gravity, its effects on objects, and the laws of gravitation formulated by Sir Isaac Newton. **Key Concepts:** 1. **Gravitational Force:** - Gravitational force is the force of attraction between all objects with mass. - It is responsible for the weight of an object and keeps celestial bodies in motion. 2. **Newton's Law of Universal Gravitation:** - Newton's law states that every mass attracts every other mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. - F = G * (m1 * m2) / r^2, where F is the force of gravity, G is the universal gravitational constant, m1 and m2 are the masses of two objects, and r is the distance between their centers. 3. **Acceleration Due to Gravity:** - Near the Earth's surface, the acceleration due to gravity (g) is approximately 9.8 m/s². - The weight of an object can be calculated as W = m * g, where W is weight, m is mass, and g is the acceleration due to gravity. 4. **Free Fall and Terminal Velocity:** - Free fall occurs when an object falls under the influence of gravity with no other forces acting on it. - As an object falls, it accelerates until it reaches terminal velocity, the maximum velocity it can attain during free fall. 5. **Orbital Motion:** - Objects in orbit, such as satellites and planets, follow a curved path due to the gravitational pull of a larger body. - This motion is governed by the principles of centripetal force and gravitational force. 6. **Weightlessness:** - Weightlessness occurs when an object experiences free fall or is in orbit, causing a sensation of weightlessness despite the absence of gravity. **Practical Applications:** - Understanding gravitation is essential for space exploration, satellite technology, and celestial mechanics. It also plays a crucial role in everyday activities like calculating weight and designing transportation systems. **Conclusion:** This chapter introduces students to the concept of gravitation, the universal law of gravitation, and its effects on objects. It provides insights into the force that governs the motion of celestial bodies and has practical applications in various fields of science and engineering.

Questions and Answers on NCERT Class 9 Science Chapter on Gravitation
Let's explore some questions and answers related to the NCERT Class 9 Science Chapter on Gravitation. Always remember to refer to your textbook for detailed information and additional practice. ### Questions and Answers: #### Q1: Define gravitation. **A1**: Gravitation is a force of attraction that acts between any two masses, any two bodies, any two particles. It is not necessary that the bodies must be in contact with each other. #### Q2: State the Universal Law of Gravitation. **A2**: The Universal Law of Gravitation states that every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. Mathematically, ( F = frac{{G cdot m_1 cdot m_2}}{{r^2}} ), where: - ( F ) is the gravitational force, - ( m_1 ) and ( m_2 ) are the masses of the particles, - ( r ) is the distance between the centers of the two masses, and - ( G ) is the gravitational constant. #### Q3: What is the significance of the G (Gravitational Constant)? **A3**: The gravitational constant ( (G) ) is a scalar quantity that describes the magnitude of gravitational force between two bodies. Its value is ( 6.674 times 10^{-11} , Nm^2/kg^2 ) in the SI system. ( G ) is a universal constant, meaning its value is the same throughout the universe and does not change with the properties or positions of the bodies involved. #### Q4: Explain the term "free fall." **A4**: Free fall is the motion of an object under the influence of gravitational force only, assuming no other forces (like air resistance) are acting on it. During free fall, objects accelerate towards the center of the Earth at a constant rate, known as the acceleration due to gravity ( (g) ). #### Q5: Differentiate between weight and mass. **A5**: Mass is a scalar quantity representing the amount of matter in an object, and it remains constant regardless of its location. Weight, on the other hand, is a vector quantity and is the force of gravity acting on an object. Unlike mass, weight varies depending on the gravitational pull at a particular location. Mathematically, Weight ( (W) = text{mass} (m) times text{gravity} (g) ). #### Q6: What is the acceleration due to gravity? **A6**: The acceleration due to gravity ( (g) ) is the acceleration experienced by an object due to the gravitational pull of a massive celestial body like a planet or moon. On the surface of the Earth, ( g ) is approximately ( 9.8 , m/s^2 ). #### Q7: Why do astronauts experience weightlessness in space? **A7**: Astronauts experience weightlessness in space because they are in a state of free fall towards the Earth, but their forward velocity is large enough to ensure they do not collide with it. Because they are in constant free fall, there is no normal reaction force acting on them, making them feel weightless. #### Q8: How is the weight of an object on the moon related to its weight on Earth? **A8**: The gravitational acceleration on the moon is about 1/6th of that on Earth. Consequently, the weight of an object on the moon is 1/6th of its weight on Earth, while its mass remains the same. Mathematically, if ( W_E ) is the weight on Earth and ( W_M ) is the weight on the Moon, ( W_M = W_E/6 ). #### Q9: What is the importance of the gravitational force? **A9**: Gravitational force is crucial as it is responsible for keeping planets in orbit around the sun, moons orbiting planets, and forming galaxies. It also governs tides on Earth, affects the atmospheric conditions, and is vital for keeping objects grounded on celestial bodies. #### Q10: Can gravitational force be repulsive? **A10**: No, gravitational force is always attractive. It acts to pull two masses toward each other and never to push them apart. By working through these questions and your NCERT Class 9 Science textbook, you will solidify your understanding of gravitation. It's always a great idea to go beyond and think of additional questions that might be asked to challenge yourself further!

Exam notes on NCERT Class 9 Science Chapter on Work, Energy and Power
Some exam notes on NCERT Class 9 Science Chapter - "Work, Energy, and Power": **Chapter Overview:** "Work, Energy, and Power" in Class 9 Science explores the concepts of work, energy, and power and how they relate to physical processes. It covers the definitions, units, and calculations related to these concepts. **Key Concepts:** 1. **Work:** - Work is done when a force acts on an object and causes it to move in the direction of the force. - Work (W) is calculated as W = Force (F) × Displacement (d) × cos(θ), where θ is the angle between the force and displacement vectors. 2. **Energy:** - Energy is the capacity to do work. - The SI unit of energy is the joule (J). 3. **Forms of Energy:** - There are various forms of energy, including kinetic energy (energy of motion), potential energy (energy due to position), mechanical energy (sum of kinetic and potential energy), and others like thermal, chemical, and nuclear energy. 4. **Kinetic Energy:** - Kinetic energy (KE) is calculated as KE = (1/2) × mass (m) × velocity (v)^2. 5. **Potential Energy:** - Gravitational potential energy (GPE) is calculated as GPE = mass (m) × gravitational acceleration (g) × height (h). - Elastic potential energy is associated with objects that can be stretched or compressed, and it depends on the spring constant and the amount of deformation. 6. **Conservation of Mechanical Energy:** - In the absence of non-conservative forces like friction, the total mechanical energy (sum of kinetic and potential energy) of an isolated system remains constant. 7. **Power:** - Power (P) is the rate at which work is done or the rate at which energy is transferred or converted. - Power is calculated as P = Work (W) / Time (t) or P = Force (F) × Velocity (v). 8. **Horsepower:** - Horsepower (hp) is a unit of power commonly used for engines and machinery. 1 horsepower is approximately equal to 746 watts. 9. **Efficiency:** - Efficiency is a measure of how effectively energy is converted or transferred in a system. - Efficiency (η) is calculated as (Useful energy output / Total energy input) × 100%. **Practical Applications:** - Understanding the concepts of work, energy, and power is essential for various engineering, scientific, and technological applications, including designing machines, calculating energy consumption, and optimizing energy use. **Conclusion:** This chapter provides students with a comprehensive understanding of work, energy, and power, including their definitions, calculations, and real-world applications. It lays the foundation for further studies in physics and engineering.

Questions and Answers on NCERT Class 9 Science Chapter on Work, Energy and Power
"Work, Energy and Power" is a fundamental chapter in Class 9 NCERT Science that explores several critical concepts in Physics. Here are some potential questions and answers based on this chapter. ### Questions and Answers: #### Q1: Define work. **A1**: Work is defined as the product of the force applied to an object and the distance over which the force is applied in the direction of the force. Mathematically, ( text{Work} (W) = text{Force} (F) times text{Displacement} (s) ). #### Q2: What is energy and name its SI unit? **A2**: Energy is the capacity of an object to do work. The SI unit of energy is the Joule, symbolized as J. #### Q3: Explain the Law of Conservation of Energy. **A3**: The Law of Conservation of Energy states that energy cannot be created or destroyed; it can only be converted from one form to another. The total energy in an isolated system remains constant over time. #### Q4: What is kinetic energy? **A4**: Kinetic energy is the energy possessed by an object due to its motion. It is given by the formula: ( KE = frac{1}{2}mv^2 ), where ( m ) is the mass and ( v ) is the velocity of the object. #### Q5: Define potential energy. **A5**: Potential energy is the energy possessed by an object due to its position or configuration. For an object at height ( h ), the gravitational potential energy is given by ( PE = mgh ), where ( m ) is mass, ( g ) is the gravitational acceleration, and ( h ) is the height. #### Q6: How is work and energy related? **A6**: Work and energy are closely related concepts. When work is done on an object, energy is transferred to or from the object. The energy transfer is equal to the work done, which can be mathematically represented as: ( text{Work Done} = text{Change in Energy} ). #### Q7: What is power and its SI unit? **A7**: Power is the rate at which work is done or the rate at which energy is transferred or converted. The SI unit of power is the Watt (W). Mathematically, ( text{Power} = frac{text{Work Done}}{text{Time Taken}} ) or ( P = frac{W}{t} ). #### Q8: Explain the transformation of energy with an example. **A8**: Energy can be transformed from one form to another. For example, in a hydroelectric power plant, the gravitational potential energy of water stored in a dam is transformed into kinetic energy as it falls. This kinetic energy is then converted into electrical energy through turbines and generators. #### Q9: Is it possible for a body to have energy without motion? **A9**: Yes, a body can have energy without motion in the form of potential energy. For instance, an object placed at a height has gravitational potential energy even when it is not moving. #### Q10: What is the work done in lifting a body vertically upward? **A10**: When a body is lifted vertically upward, the work done (W) is equal to the product of the force used (F), the displacement or height (h), and the cosine of the angle between the force and displacement (θ). Since the force and displacement are in the same direction (θ = 0°), ( W = F times h times cos 0° = F times h ). #### Q11: What determines the potential energy of an object? **A11**: The potential energy of an object is determined by its position or configuration, mass, and height in the gravitational field (for gravitational potential energy). Mathematically, ( PE = mgh ), where m is mass, g is gravitational acceleration, and h is height. #### Q12: Why is no work done by the force of gravity when we carry a book and walk horizontally? **A12**: No work is done by the force of gravity when we carry a book and walk horizontally because the gravitational force and the direction of displacement are perpendicular to each other. Mathematically, since ( text{Work} = F times s times cos theta ) and ( theta = 90^circ ), the work done is zero because ( cos 90^circ = 0 ). These questions and answers cover various fundamental concepts of work, energy, and power as per the NCERT Class 9 Science curriculum. Always ensure to practice additional questions and understand the concepts thoroughly to perform well in your exams.

Exam notes on NCERT Class 9 Science Chapter on Improvement in Food Resources
Some exam notes on NCERT Class 9 Science Chapter - "Improvement in Food Resources": **Chapter Overview:** "Improvement in Food Resources" in Class 9 Science focuses on various aspects of agriculture, animal husbandry, and different methods to enhance food production to meet the growing global demand for food. **Key Concepts:** 1. **Agriculture:** - Agriculture is the practice of growing crops and raising livestock for food and other agricultural products. - It is a primary source of food production. 2. **Crops:** - Crops are cultivated plants that are grown for food, fiber, or other commercial purposes. - Crop production is influenced by factors like climate, soil type, and water availability. 3. **Types of Crops:** - Crops are categorized as food crops (e.g., cereals, pulses) and cash crops (e.g., cotton, sugarcane). - Mixed cropping and crop rotation are agricultural practices used to enhance crop yield and soil fertility. 4. **Crop Production Management:** - Proper management practices, including selection of seeds, soil preparation, sowing, irrigation, and use of fertilizers and pesticides, are essential for high crop yield. 5. **Animal Husbandry:** - Animal husbandry involves the breeding, care, and management of domestic animals for various purposes, including milk, meat, and wool production. 6. **Poultry Farming:** - Poultry farming is the rearing of birds like chickens and ducks for meat and egg production. 7. **Fish Farming:** - Fish farming, also known as aquaculture, is the controlled cultivation of fish in ponds, tanks, or other water bodies. 8. **Beekeeping:** - Beekeeping involves the maintenance of bee colonies for honey production and pollination. 9. **Biotechnology in Agriculture:** - Biotechnology has been used to develop genetically modified (GM) crops that are resistant to pests, diseases, and adverse environmental conditions. 10. **Organic Farming:** - Organic farming is a sustainable and eco-friendly approach that avoids synthetic chemicals and focuses on natural methods of pest control and soil enrichment. **Practical Applications:** - The chapter highlights the importance of efficient agricultural practices, animal husbandry, and sustainable food production methods to ensure food security and meet the nutritional needs of the growing global population. **Conclusion:** This chapter provides students with insights into various aspects of food production, including agriculture, animal husbandry, and modern farming techniques. It emphasizes the importance of sustainable practices and the role of technology in enhancing food resources to meet the demands of the future.

Questions and Answers on NCERT Class 9 Science Chapter on Improvement in Food Resources
"Improvement in Food Resources" is a vital chapter in NCERT Class 9 Science that discusses how the enhancement and management of food resources is crucial to meet the nutritional requirements of the ever-growing human population. Below are some questions and their answers based on this chapter: ### Questions and Answers: #### Q1: Define crop rotation and its importance. **A1**: Crop rotation involves growing different crops in succession on the same land to maintain soil fertility and structure. Its importance lies in preventing soil depletion, controlling pests and diseases, and enhancing soil nutrient content. #### Q2: Differentiate between Rabi and Kharif crops. **A2**: - **Rabi Crops**: Sown in winter (October to December) and harvested in summer (April to June). Examples include wheat and mustard. - **Kharif Crops**: Sown with the onset of monsoon (June to July) and harvested in autumn (September to October). Examples include rice and maize. #### Q3: What is animal husbandry? **A3**: Animal husbandry refers to the practice of breeding and caring for animals that are useful to humans, such as cattle, poultry, and fish. It involves management practices to enhance the yield of products like milk, meat, and eggs. #### Q4: Define poultry farming and mention two of its objectives. **A4**: Poultry farming involves raising domesticated birds, such as chickens, ducks, and turkeys, for their meat and eggs. Objectives include providing protein-rich food (meat and eggs) to humans and creating employment opportunities. #### Q5: What is fishery? Name two types of fish farming. **A5**: Fishery involves catching, processing, and selling fish, shellfish, and other aquatic organisms. Two types of fish farming are: - **Mariculture**: Cultivation of marine organisms in their natural habitats. - **Aquaculture**: Breeding and harvesting of fish in controlled freshwater ponds and rice fields. #### Q6: How are crops classified based on the season? **A6**: Crops can be classified based on the season as: - **Rabi Crops**: Grown in the winter season. - **Kharif Crops**: Grown in the monsoon season. - **Zaid Crops**: Short-duration crops grown between Rabi and Kharif seasons (e.g., cucumber, bitter gourd). #### Q7: How is soil fertility replenished in organic farming? **A7**: In organic farming, soil fertility is replenished through natural processes like using organic manure, compost, vermicompost, and practicing crop rotation and mixed cropping to enhance nutrient availability and balance in the soil. #### Q8: What is mixed farming? **A8**: Mixed farming refers to the practice of cultivating crops alongside rearing animals on the same farmland. It provides a diverse source of income and ensures optimal utilization of resources like fodder and manure. #### Q9: Explain the term ‘Green Revolution’. **A9**: The Green Revolution refers to a set of research, development, and technology transfer initiatives, occurring between the 1960s and the 1980s, which significantly increased agriculture production around the world, particularly in developing countries, through the use of high-yielding varieties of cereals, chemical fertilizers, and pesticides. #### Q10: Mention the importance of beekeeping in agriculture. **A10**: Beekeeping or apiculture is vital for: - **Pollination**: Bees play a crucial role in pollinating flowers, thereby aiding in the reproduction of flowering plants. - **Honey Production**: Bees produce honey, which has nutritional and medicinal values. - **Wax Production**: Beeswax is used in cosmetics and as a sealant. #### Q11: What is the significance of biofortification? **A11**: Biofortification refers to the process of increasing the nutritional quality of crops through genetic breeding. Its significance lies in: - Enhancing the nutritional content of crops. - Addressing issues related to malnutrition and nutrient deficiencies. - Making nutrient-dense food available to the population. #### Q12: Why is crop protection important? **A12**: Crop protection is important to: - Shield crops from pests, weeds, and diseases. - Ensure high-quality yield. - Improve food production and food security. - Reduce economic losses for farmers. These questions and answers encompass key concepts related to improving food resources as outlined in the NCERT Class 9 Science curriculum. Make sure to delve into each topic in the chapter for comprehensive exam preparation.

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