Chattisgarh Vacancy
NCERT Class 9 Science Notes — English Medium
Learn Science in easy English with important notes, labelled diagrams, chapter summaries, questions and answers, MCQs and quick revision points.
Detailed notes on this page: Chapter 2 — Cell: The Building Block of Life, and Chapter 3 — Tissues in Action.
Welcome to Class 9 Science Study Notes
Science becomes easier when you understand the concepts rather than memorising every line. These notes explain key ideas in simple language and help you prepare for classroom tests and examinations.
📘 Easy explanations
Learn important concepts with familiar examples and simple definitions.
🔬 Diagrams and tables
Understand cell structure, plant tissues, animal tissues and their functions.
✍️ Questions and answers
Practise short answers, long answers and multiple-choice questions.
✅ Quick revision
Review key facts before your test with chapter summaries and memory tips.
NCERT Class 9 Science — Chapter Guide
Chapters 2 and 3 are explained in detail below. Chapter 9 has a separate detailed Vacancy99 study page. For other chapters, use the official NCERT resource directory until a dedicated Vacancy99 notes page is available.
The NCERT ePathshala link is a resource directory, not an individual Vacancy99 chapter page. Open it and select the textbook or chapter relevant to your edition.
Cell: The Building Block of Life
In the older notes this topic may also be called “Cell: The Fundamental Unit of Life.” A cell is the basic structural and functional unit of life. Just as bricks make a building, cells make up plants, animals and other living organisms.
1. What Is a Cell?
A cell is the smallest structural and functional unit of a living organism. It carries out essential life activities. Some organisms consist of only one cell, while plants and animals are made up of many cells.
- Unicellular organisms: made up of one cell. Examples include many bacteria and Amoeba.
- Multicellular organisms: made up of many cells. Examples include humans, dogs and mango trees.
- Specialised cells: cells adapted to perform particular functions, such as muscle cells and nerve cells.
2. Who Discovered the Cell?
In 1665, Robert Hooke examined a thin slice of cork through a microscope. He observed tiny box-like compartments and named them “cells.” Cork is dead plant tissue, so Hooke saw the outlines of its cells.
Later, scientists studied living cells and helped develop cell theory.
Main points of cell theory
- All living organisms are made up of one or more cells.
- The cell is the basic structural and functional unit of life.
- New cells arise from pre-existing cells.
3. Main Parts of a Cell
Cell membrane
The thin boundary around a cell. It protects the cell and regulates the movement of substances into and out of it. It is selectively permeable.
Cytoplasm
The material inside the cell membrane, outside the nucleus. Most organelles are located in it, and many chemical reactions occur there.
Nucleus
Contains genetic material, including DNA, and helps regulate cell activities. It plays an important role in inheritance.
Cell wall
A rigid outer layer outside the cell membrane in plant cells. It provides support and protection. Animal cells do not have a cell wall.
4. Cell Organelles and Their Functions
Cell organelles are specialised structures inside cells. Each performs particular functions that help the cell survive and work efficiently.
| Organelle | Function | Easy way to remember |
|---|---|---|
| Nucleus | Contains DNA and helps regulate cell activities. | Control centre |
| Mitochondria | Carry out cellular respiration and release usable energy from food molecules. | Energy supply |
| Ribosomes | Make proteins needed for growth, repair and cell functions. | Protein makers |
| Golgi apparatus | Modifies, sorts and packages proteins and lipids. | Packing centre |
| Rough ER | Has ribosomes attached and helps in protein production and processing. | Protein-related work |
| Smooth ER | Lacks attached ribosomes; helps make lipids and carries out other functions. | Lipid production |
| Lysosomes | Contain enzymes that break down waste and worn-out cell components. | Cleaning and recycling |
| Chloroplasts | Contain chlorophyll and carry out photosynthesis in photosynthetic plant cells. | Food-making site |
| Vacuoles | Store water and other materials. The large central plant vacuole helps maintain firmness. | Storage |
5. Plant Cell vs Animal Cell
| Plant cell | Animal cell |
|---|---|
| Cell wall is present. | Cell wall is absent. |
| Chloroplasts occur in photosynthetic plant cells. | Chloroplasts are absent. |
| Usually has a large central vacuole. | Vacuoles are generally smaller, and their presence and size vary. |
| Shape is often more regular because of the cell wall. | Shape varies according to the cell's function. |
| Has a cell membrane, cytoplasm, DNA and ribosomes. | Has a cell membrane, cytoplasm, DNA and ribosomes. |
6. Diffusion and Osmosis
Diffusion
The net movement of particles from a region of higher concentration to a region of lower concentration.
Example: The smell of perfume spreading through a room.
Osmosis
The net movement of water through a selectively permeable membrane down its water-concentration gradient.
Example: Water entering plant root cells.
7. Important Questions and Answers — Chapter 2
Click each question to open its answer. Try answering before you reveal the explanation.
Q1. What is a cell?
Q2. Who discovered the cell?
Q3. State the main points of cell theory.
Q4. Why is the cell membrane called selectively permeable?
Q5. What is the function of the cytoplasm?
Q6. Why is the nucleus called the control centre?
Q7. Why are mitochondria called the powerhouse of the cell?
Q8. What is the function of ribosomes?
Q9. Differentiate between rough ER and smooth ER.
Q10. What does the Golgi apparatus do?
Q11. What is the function of lysosomes?
Q12. Why are chloroplasts important?
Q13. Give four differences between plant and animal cells.
Q14. Explain diffusion with an example.
Q15. What is osmosis? How is it different from diffusion?
Q16. Why do multicellular organisms need specialised cells?
8. Important MCQs — Chapter 2
1. What is the basic unit of life?
A. Tissue B. Organ C. Cell D. Organ system
Show answer
Correct answer: C. Cell
2. Who observed cork cells in 1665?
A. Newton B. Robert Hooke C. Darwin D. Mendel
Show answer
Correct answer: B. Robert Hooke
3. Which organelle is associated with cellular respiration?
A. Ribosome B. Mitochondrion C. Vacuole D. Golgi apparatus
Show answer
Correct answer: B. Mitochondrion
4. Protein synthesis takes place at:
A. Ribosomes B. Vacuoles C. Cell wall D. Chlorophyll
Show answer
Correct answer: A. Ribosomes
5. Which structure is absent in animal cells?
A. Cell membrane B. Cytoplasm C. Cell wall D. Ribosomes
Show answer
Correct answer: C. Cell wall
6. Which pigment helps plants absorb light for photosynthesis?
A. Haemoglobin B. Chlorophyll C. Melanin D. Keratin
Show answer
Correct answer: B. Chlorophyll
Chapter 2 — Two-Minute Revision
- Cell = basic unit of life.
- Robert Hooke observed cork cells in 1665.
- Nucleus = DNA and regulation of cell activities.
- Mitochondria = cellular respiration and energy release.
- Ribosomes = protein synthesis.
- Golgi apparatus = modification, sorting and packaging.
- Chloroplasts = photosynthesis in photosynthetic plant cells.
- Cell wall = support and protection in plant cells.
- Diffusion = net movement of particles from higher to lower concentration.
- Osmosis = movement of water through a selectively permeable membrane.
Tissues in Action
If every cell in our body had to perform every function, the body would not work efficiently. Cells with specialised structures work together in groups called tissues. Plant tissues help plants grow, support themselves and transport materials. Animal tissues provide protection, support, movement and communication.
1. What Is a Tissue?
A tissue is a group of cells organised to perform a particular function. The cells in a tissue may have similar structures and work together to carry out that function.
Easy example — a cricket team
A cricket team has batters, bowlers and a wicketkeeper. Each has a specialised role, but all work together for the same goal. Similarly, different tissues perform specialised jobs in a living organism.
2. Why Do We Need Tissues?
- They divide work among specialised groups of cells.
- They help organisms perform functions efficiently.
- They enable growth, transport, protection and movement.
- They help complex organisms carry out many activities at the same time.
3. Plant Tissues
Plant tissues are broadly classified into meristematic tissues and permanent tissues.
A. Meristematic tissue
Definition: Meristematic tissue consists of cells that actively divide and produce new cells. It enables plant growth.
Functions: increases plant length, increases stem and root thickness, and produces new growing parts.
Types of meristematic tissue
- Apical meristem: found at root and shoot tips; increases plant length.
- Lateral meristem: found along the sides of stems and roots; increases thickness or girth.
- Intercalary meristem: found near nodes or at leaf bases in many grasses; helps growth and regrowth after cutting or grazing.
Characteristics
- Cells are living and actively dividing.
- Cells are closely packed.
- Cell walls are generally thin.
- There are very few or no intercellular spaces.
B. Permanent tissue
Permanent tissues form when cells become specialised for particular functions. They generally lose some or most of their ability to divide.
Simple permanent tissues
- Parenchyma: stores food and water; in some plant parts, it performs photosynthesis and helps in repair.
- Collenchyma: provides flexible support and allows young stems and leaves to bend without breaking easily.
- Sclerenchyma: provides strength and rigidity. Mature cells are usually dead and have thick, lignified walls.
Complex permanent tissues
- Xylem: transports water and minerals from roots to other plant parts and also provides support.
- Phloem: transports sugars and other organic nutrients from sources, such as leaves, to parts where they are used or stored.
4. Animal Tissues
Animals have four major types of tissues: epithelial, connective, muscular and nervous.
A. Epithelial tissue
Covers body surfaces and lines many organs and cavities.
Functions: protection, absorption, secretion and exchange of substances.
Examples: skin, lining of the mouth and lining of the intestine.
Memory tip: Epithelial = covering and protection.
B. Connective tissue
Supports, binds or connects different body parts. Its cells are often embedded in an extracellular matrix.
Examples: blood, bone, cartilage, tendons, ligaments and adipose tissue.
Memory tip: Connective = connecting and support.
C. Muscular tissue
Contracts to produce movement. It has three main types:
- Skeletal muscle: usually voluntary; moves bones.
- Smooth muscle: involuntary; found in organs such as the intestine.
- Cardiac muscle: involuntary muscle found in the heart; pumps blood.
Memory tip: Muscular = movement.
D. Nervous tissue
Receives and transmits information. The main specialised cell is the neuron.
Functions: carries signals between the brain, spinal cord and other parts of the body and helps the body respond to stimuli.
Memory tip: Nervous = messages.
5. Plant Tissues and Animal Tissues — Comparison
| Plant tissues | Animal tissues |
|---|---|
| Meristematic tissue helps plant growth. | Different tissues support growth and specialised body functions. |
| Xylem transports water and minerals. | Blood transports oxygen, nutrients and other substances. |
| Phloem transports sugars and organic nutrients. | Connective tissues support, bind or connect body structures. |
| Collenchyma and sclerenchyma provide support. | Bone and cartilage support the body and protect structures. |
| Plant tissues are adapted to growth, support and transport. | Animal tissues are adapted to protection, support, movement and communication. |
6. Musculoskeletal System
The musculoskeletal system includes bones, muscles, joints and associated connective tissues. They work together to support the body and enable movement.
Bones + Muscles + Joints = A working movement system.
Functions of bones
- Give shape and support to the body.
- Protect internal organs.
- Work with muscles to help movement.
- Store minerals such as calcium and phosphorus.
- Bone marrow produces blood cells in many bones.
Muscles, tendons and ligaments
- Muscles: contract to generate force and movement.
- Tendons: connect muscles to bones.
- Ligaments: connect bones to bones and help stabilise joints.
- Joints: places where two or more bones meet.
7. Types of Joints
| Joint type | Movement | Example |
|---|---|---|
| Fixed or immovable | Little or no movement | Many joints between skull bones |
| Ball-and-socket | Movement in many directions | Shoulder and hip |
| Hinge | Mainly bending and straightening | Elbow and knee |
| Pivot | Rotation around an axis | Joint between the first two neck vertebrae |
| Gliding | Small sliding movements | Some joints in the wrist |
8. Correct Posture, Exercise and Bone Care
Good posture habits
- Sit with your back comfortably supported.
- Avoid bending your neck excessively while using a phone.
- Take movement breaks during long study sessions.
- Carry a heavy school bag using both shoulder straps.
Why is exercise important?
- Helps maintain muscle strength.
- Supports bone health.
- Improves flexibility, balance and fitness.
- Helps maintain a healthy body weight.
How to care for bones
- Eat a balanced diet with calcium-rich foods.
- Get sufficient vitamin D.
- Do appropriate weight-bearing activity.
- Take precautions to prevent falls and injuries.
Everyday reminder
Healthy movement depends on more than bones alone. Muscles, joints, connective tissues, nutrition, rest and suitable physical activity all contribute.
9. Important Questions and Answers — Chapter 3
Q1. What is a tissue?
Q2. Why are tissues important in multicellular organisms?
Q3. What is meristematic tissue?
Q4. Differentiate between apical, lateral and intercalary meristems.
Q5. State the characteristics of meristematic tissue.
Q6. What is permanent tissue?
Q7. Name the three main simple permanent tissues in plants.
Q8. Explain the functions of parenchyma, collenchyma and sclerenchyma.
Q9. Differentiate between xylem and phloem.
Q10. Name the four major types of animal tissues.
Q11. What are the functions of epithelial tissue?
Q12. What is connective tissue? Give examples.
Q13. Explain the three types of muscular tissue.
Q14. What is nervous tissue? What is the role of a neuron?
Q15. Differentiate between tendons and ligaments.
Q16. What is the musculoskeletal system?
Q17. Explain any three types of joints with examples.
Q18. Why is regular exercise important for bones and muscles?
10. Important MCQs — Chapter 3
1. A group of cells organised to perform a particular function is called:
A. Organism B. Tissue C. Molecule D. Organ system
Show answer
Correct answer: B. Tissue
2. Which tissue is responsible for plant growth?
A. Meristematic B. Nervous C. Muscular D. Epithelial
Show answer
Correct answer: A. Meristematic
3. Which plant tissue transports water and minerals?
A. Phloem B. Xylem C. Nervous tissue D. Muscular tissue
Show answer
Correct answer: B. Xylem
4. Which plant tissue provides flexible support?
A. Collenchyma B. Phloem C. Nervous tissue D. Blood
Show answer
Correct answer: A. Collenchyma
5. Which animal tissue contracts to produce movement?
A. Epithelial B. Muscular C. Nervous D. Blood plasma
Show answer
Correct answer: B. Muscular
6. Which tissue transmits electrical signals?
A. Nervous B. Sclerenchyma C. Xylem D. Cartilage
Show answer
Correct answer: A. Nervous
7. Tendons connect:
A. Bone to bone B. Muscle to bone C. Nerve to nerve D. Skin to hair
Show answer
Correct answer: B. Muscle to bone
Chapter 3 — Two-Minute Revision
Plant tissues
- Meristematic → growth.
- Parenchyma → storage and sometimes photosynthesis.
- Collenchyma → flexible support.
- Sclerenchyma → strength and rigidity.
- Xylem → water and minerals.
- Phloem → sugars and organic nutrients.
Animal tissues
- Epithelial → covering and protection.
- Connective → connecting and support.
- Muscular → movement.
- Nervous → messages and signals.
Musculoskeletal system
- Bones + muscles + joints → movement and support.
- Ball-and-socket → shoulder and hip.
- Hinge → elbow and knee.
- Pivot → neck.
- Gliding → some wrist joints.
- Tendon → muscle to bone; ligament → bone to bone.
Chapter 3 — Summary
Plants and animals have different types of tissues, and each tissue performs particular functions. In plants, meristematic tissues help growth, permanent tissues perform specialised functions, xylem transports water and minerals, and phloem transports sugars and other organic nutrients.
In animals, epithelial tissue covers and protects, connective tissue supports and connects, muscular tissue produces movement, and nervous tissue transmits information. Bones, muscles and joints work together as part of the musculoskeletal system.
How to Prepare for Your Science Examination
- Read the textbook section first and understand the meaning of each key term.
- Study the diagrams and practise drawing them with labels.
- Learn comparisons such as plant cell versus animal cell and xylem versus phloem.
- Answer the questions on this page without looking at the answers first.
- Use the MCQs to identify topics that need more revision.
- Review the two-minute revision lists before your test.
