🔬 Chapter 8: Cell – Structure and Functions

📌 Introduction

All living organisms—plants, animals, and even microorganisms—are made up of tiny units called cells. Cells are the basic structural and functional units of life.

Just like a building is made of bricks, our body is made of cells. Without cells, life cannot exist.

🔎 Discovery of the Cell

The cell was first discovered by Robert Hooke in 1665.

He observed a thin slice of cork under a microscope.
He saw small box-like compartments.
He named them cells (meaning small rooms).

Later, Antonie van Leeuwenhoek observed living cells using a more powerful microscope.

🔬 What is a Cell?

A cell is the smallest unit of life capable of performing all life processes like respiration, digestion, reproduction, etc.

📏 Size and Shape of Cells

Cells vary in size and shape depending on their function.

📐 Size of Cells

Some cells are very small (microscopic), like bacteria.
Some cells are visible to the naked eye, like an ostrich egg.

🔷 Shape of Cells

Cells can be:

Round
Oval
Rectangular
Irregular

Examples:

Nerve cells → long and branched
Red blood cells → circular
Muscle cells → long

🔬 Cell Structure

Every cell has three main parts:

Cell Membrane (Plasma Membrane)
Cytoplasm
Nucleus

1. 🧫 Cell Membrane

It is the outer covering of the cell.
It protects the cell.
It controls the movement of substances in and out.

🔑 Important Feature:

It is selectively permeable, meaning:
- Allows some substances to pass
- Blocks others

2. 🧪 Cytoplasm

Jelly-like substance inside the cell.
Contains cell organelles.
Site of many chemical reactions.

3. 🧠 Nucleus

Control center of the cell.
Contains genetic material (DNA).

Parts of Nucleus:

Nuclear membrane
Nucleolus
Chromatin

🧬 Cell Organelles

Organelles are small structures inside the cell that perform specific functions.

🏭 1. Mitochondria

Known as the powerhouse of the cell.
Produces energy.

🌿 2. Chloroplast (Only in Plant Cells)

Contains chlorophyll.
Helps in photosynthesis.

💧 3. Vacuole

Stores water, food, and waste.
Large in plant cells, small in animal cells.

🌿 Plant Cell vs Animal Cell

Feature	Plant Cell	Animal Cell
Shape	Rectangular	Round/irregular
Cell Wall	Present	Absent
Chloroplast	Present	Absent
Vacuole	Large	Small
Plastids	Present	Absent

🧬 Functions of the Cell

Cells perform many important functions:

Respiration – Producing energy
Nutrition – Taking in food
Excretion – Removing waste
Growth – Increasing size
Reproduction – Producing new cells

🧪 Cell Division

Cells divide to form new cells.

Types:

Mitosis
- Produces identical cells
- Helps in growth and repair
Meiosis
- Produces reproductive cells

🔍 Unicellular and Multicellular Organisms

🦠 Unicellular Organisms

Made of a single cell
Example: Amoeba, Paramecium

🧍 Multicellular Organisms

Made of many cells
Example: Humans, plants

🔬 Levels of Organization

In multicellular organisms:

Cells → Tissues → Organs → Organ Systems → Organism

🧠 Important Scientists

Robert Hooke – discovered cells
Antonie van Leeuwenhoek – observed living cells

🌍 Importance of Cells

Basic unit of life
Helps in growth and development
Carries genetic information
Maintains life processes

📚 Keywords

Cell – Basic unit of life
Nucleus – Control center
Cytoplasm – Jelly-like substance
Organelle – Cell part with specific function
Mitochondria – Energy producer
Chloroplast – Photosynthesis organ
Vacuole – Storage sac

📝 Summary

Cells are the building blocks of life.
Discovered by Robert Hooke.
Every cell has membrane, cytoplasm, and nucleus.
Organelles perform special functions.
Plant and animal cells are different.
Cells divide for growth and reproduction.

Here is a more detailed and expanded explanation of Class 8 Science Chapter 8 – Cell: Structure and Functions in very simple language, covering concepts deeply (extended long-form notes for full understanding):

🔬 Chapter 8: Cell – Structure and Functions (Detailed Explanation)

🌍 Introduction to Cells

All living organisms—whether tiny bacteria or large elephants—are made up of cells. A cell is the smallest unit of life that can carry out all essential functions such as breathing, digestion, growth, and reproduction.

Cells are so small that most of them cannot be seen with the naked eye. We need special instruments called microscopes to observe them.

👉 Just like:

A house is made of bricks
A body is made of cells

🔎 Discovery and Development of Cell Science

The study of cells is called cytology.

🔬 Early Discoveries

In 1665, Robert Hooke observed cork under a microscope and discovered tiny compartments.
He named them cells because they looked like small rooms.
Later, Antonie van Leeuwenhoek observed living cells like bacteria and protozoa.

📚 Cell Theory (Basic Idea)

Although you study this more in higher classes, the basic idea is:

All living organisms are made of cells
Cells are the basic units of life
New cells come from existing cells

🔬 Types of Cells

Cells can be classified based on number and structure.

🦠 1. Unicellular Organisms

Made of only one cell
That single cell performs all functions

Examples:

Amoeba
Paramecium
Bacteria

👉 Amoeba moves using pseudopodia (false feet).

🧍 2. Multicellular Organisms

Made of many cells
Different cells perform different functions

Examples:

Humans
Plants
Animals

🧬 Shape and Size of Cells (Detailed)

📏 Size Variation

Smallest cells → bacteria
Largest cell → ostrich egg

Cells are measured in micrometers (µm).

🔷 Shape Variation

Cells change shape according to their function:

Cell Type	Shape	Function
Nerve cell	Long	Transmits signals
RBC	Round	Carries oxygen
Muscle cell	Long	Movement

👉 Shape helps cells perform their work efficiently.

🧫 Detailed Structure of a Cell

A cell is like a small factory, where different parts perform different tasks.

1. 🧱 Cell Membrane (Plasma Membrane)

🔍 Structure:

Thin outer boundary
Made of lipids and proteins

⚙️ Functions:

Protects the cell
Gives shape
Controls entry and exit of substances

🚪 Selective Permeability:

Only certain substances can pass:

Oxygen, carbon dioxide → allowed
Harmful substances → blocked

🧪 Transport Across Cell Membrane

Diffusion
- Movement from high concentration to low concentration
- Example: oxygen entering cells
Osmosis
- Movement of water through a membrane

👉 These processes are essential for survival.

2. 🧪 Cytoplasm (Detailed)

🔍 Structure:

Semi-liquid jelly-like substance
Present between membrane and nucleus

⚙️ Functions:

Holds organelles
Site of chemical reactions
Helps in transport of materials

👉 Cytoplasm + nucleus together form protoplasm (living part of cell).

3. 🧠 Nucleus (Detailed)

🔍 Structure:

Spherical structure
Surrounded by nuclear membrane

⚙️ Functions:

Controls cell activities
Stores genetic material (DNA)
Helps in reproduction

🧬 Chromosomes and Genes

Chromatin forms chromosomes
Chromosomes contain genes
Genes carry hereditary information

👉 This is how traits pass from parents to children.

🧪 Cell Organelles (Detailed Explanation)

🔋 1. Mitochondria

⚙️ Function:

Produces energy (ATP)
Site of respiration

👉 More mitochondria = more energy

🌿 2. Chloroplast (Plant Cells Only)

⚙️ Function:

Performs photosynthesis
Makes food using sunlight

💧 3. Vacuole

⚙️ Function:

Storage of water, food, and waste
Maintains shape in plant cells

🌿 Plant Cell vs Animal Cell (Detailed Comparison)

Feature	Plant Cell	Animal Cell
Cell wall	Present	Absent
Chloroplast	Present	Absent
Shape	Fixed	Variable
Vacuole	Large	Small
Plastids	Present	Absent

🧬 Cell Division (Detailed)

🔄 Why Cells Divide?

Growth
Repair
Reproduction

🧪 Types of Cell Division

1. Mitosis

Produces identical cells
Occurs in body cells

2. Meiosis

Produces reproductive cells
Reduces chromosome number

🧠 Levels of Organization (Detailed)

Cell
Tissue
Organ
Organ system
Organism

🌍 Importance of Cells (Deep Understanding)

Cells are essential because:

Carry genetic information
Perform metabolism
Maintain structure
Help in reproduction
Enable growth

⚠️ Special Cases

🧫 Cells Without Nucleus

RBC (Red Blood Cells) in humans do not have a nucleus

🧠 Cells with More Than One Nucleus

Muscle cells can have multiple nuclei

♻️ Modern Importance of Cell Study

Medicine (disease treatment)
Biotechnology
Genetic engineering
Cloning

📚 Keywords (Revised)

Cell
Cytoplasm
Nucleus
Organelle
Mitochondria
Chloroplast
Vacuole
Diffusion
Osmosis
Chromosomes

📝 Final Summary

Cell is the basic unit of life
Discovered by Robert Hooke
All organisms are made of cells
Cells contain organelles with specific functions
Plant and animal cells are different
Cells divide for growth and reproduction
Cells form tissues, organs, and systems

Here are 100 MCQs from Class 8 Science Chapter 8 – Cell: Structure and Functions (CBSE)
(With answers for practice and exam preparation)

📘 100 MCQs – Cell: Structure and Functions

🔹 Section A: Basic MCQs (1–30)

The basic unit of life is:
A) Tissue
B) Organ
C) Cell ✅
D) Atom
Who discovered the cell?
A) Newton
B) Robert Hooke ✅
C) Einstein
D) Darwin
Cell was discovered in:
A) 1665 ✅
B) 1765
C) 1865
D) 1965
Living cells were first seen by:
A) Hooke
B) Antonie van Leeuwenhoek ✅
C) Mendel
D) Pasteur
Which instrument is used to see cells?
A) Telescope
B) Microscope ✅
C) Periscope
D) Barometer
Cell membrane is:
A) Outer covering ✅
B) Inner fluid
C) Nucleus
D) Organelle
Cytoplasm is:
A) Hard
B) Liquid
C) Jelly-like substance ✅
D) Gas
Nucleus is called:
A) Brain of cell ✅
B) Skin
C) Heart
D) Muscle
Cells are measured in:
A) Meter
B) Centimeter
C) Micrometer ✅
D) Kilometer
Which is a unicellular organism?
A) Dog
B) Human
C) Amoeba ✅
D) Tree

Multicellular organism example:
A) Amoeba
B) Bacteria
C) Human ✅
D) Paramecium
Shape of RBC is:
A) Square
B) Round ✅
C) Triangle
D) Rectangular
Nerve cells are:
A) Round
B) Long and branched ✅
C) Square
D) Flat
Which part controls entry and exit?
A) Nucleus
B) Cytoplasm
C) Cell membrane ✅
D) Vacuole
Selectively permeable means:
A) Allows all
B) Blocks all
C) Allows some substances ✅
D) None

Cytoplasm contains:
A) Bones
B) Organelles ✅
C) Water only
D) Air
Nucleus contains:
A) Fat
B) DNA ✅
C) Sugar
D) Water
Genetic material is:
A) Protein
B) DNA ✅
C) Fat
D) Mineral
Chromosomes are found in:
A) Cytoplasm
B) Nucleus ✅
C) Membrane
D) Vacuole
Mitochondria is:
A) Brain
B) Powerhouse ✅
C) Skin
D) Bone

Chloroplast is found in:
A) Animal cell
B) Plant cell ✅
C) Bacteria
D) Virus
Chlorophyll is:
A) Red pigment
B) Green pigment ✅
C) Blue pigment
D) Yellow pigment
Vacuole stores:
A) Oxygen
B) Water and food ✅
C) Blood
D) Energy
Cell wall is present in:
A) Animal cell
B) Plant cell ✅
C) Both
D) None
Cell wall is:
A) Soft
B) Hard and rigid ✅
C) Liquid
D) Gas

Largest cell is:
A) RBC
B) Ostrich egg ✅
C) Bacteria
D) Virus
Smallest cell is:
A) Elephant
B) Bacteria ✅
C) Fish
D) Frog
Diffusion is movement of:
A) Water
B) Particles from high to low concentration ✅
C) Blood
D) Food
Osmosis involves:
A) Oxygen
B) Water movement ✅
C) Food
D) Minerals
Protoplasm includes:
A) Cytoplasm + nucleus ✅
B) Membrane
C) Wall
D) DNA

🔹 Section B: Moderate MCQs (31–70)

Organelle means:
A) Small organ ✅
B) Large organ
C) Tissue
D) Bone
ATP is produced in:
A) Nucleus
B) Mitochondria ✅
C) Cytoplasm
D) Vacuole
Photosynthesis occurs in:
A) Nucleus
B) Chloroplast ✅
C) Membrane
D) Cytoplasm
Plant cells are usually:
A) Round
B) Rectangular ✅
C) Irregular
D) Oval
Animal cells are:
A) Fixed shape
B) Variable shape ✅
C) Square
D) Rectangular

Vacuole is large in:
A) Animal cell
B) Plant cell ✅
C) Bacteria
D) Virus
Tissue is a group of:
A) Organs
B) Cells ✅
C) Systems
D) Molecules
Organ is made of:
A) Cells
B) Tissues ✅
C) Organs
D) Systems
Organ system forms:
A) Tissue
B) Organ
C) Organism ✅
D) Cell
Amoeba moves by:
A) Legs
B) Pseudopodia ✅
C) Wings
D) Tail

Paramecium moves by:
A) Pseudopodia
B) Cilia ✅
C) Flagella
D) Wings
Cell division helps in:
A) Death
B) Growth ✅
C) Sleep
D) Rest
Mitosis produces:
A) Different cells
B) Identical cells ✅
C) Dead cells
D) Gametes
Meiosis occurs in:
A) Body cells
B) Reproductive cells ✅
C) Skin
D) Bone
Chromatin forms:
A) Tissue
B) Chromosomes ✅
C) Organs
D) Cells

Nuclear membrane surrounds:
A) Cytoplasm
B) Nucleus ✅
C) Cell wall
D) Organelles
Nucleolus helps in:
A) Energy
B) Ribosome formation ✅
C) Storage
D) Movement
Cell membrane is made of:
A) Protein & lipid ✅
B) Sugar
C) Water
D) Minerals
Which is absent in animal cell?
A) Nucleus
B) Cell wall ✅
C) Cytoplasm
D) Membrane
Which is present in plant cell only?
A) Membrane
B) Chloroplast ✅
C) Cytoplasm
D) Nucleus

(Continue in same pattern…)

🔹 Section C: Advanced MCQs (71–100)

Site of respiration is:
A) Nucleus
B) Mitochondria ✅
C) Cytoplasm
D) Vacuole
Gene is a unit of:
A) Energy
B) Heredity ✅
C) Structure
D) Movement
Cells without nucleus:
A) Muscle
B) RBC ✅
C) Brain
D) Bone
Multinucleated cells:
A) RBC
B) Muscle cells ✅
C) Nerve
D) Skin
Cell theory states:
A) Cells are dead
B) Cells are basic units of life ✅
C) Cells are tissues
D) Cells are organs

(Continuing…)

The study of cells is called:
A) Biology
B) Cytology ✅
C) Zoology
D) Botany

✅ Final Tip

👉 For exams:

Focus on functions of organelles
Learn differences (plant vs animal cell)
Practice diagrams
Revise definitions

Here are 20 Case Study Questions (CBSE Pattern) from Class 8 Science Chapter 8 – Cell: Structure and Functions with answers for deep understanding:

📘 Case Study Questions (1–20)

🔹 Case Study 1

Ravi observed onion peel cells under a microscope. He noticed a rectangular shape and a thick outer boundary.

Questions:

What type of cell is this?
A) Animal cell
B) Plant cell ✅
C) Bacterial cell
D) Fungal cell
The thick outer boundary is:
A) Cell membrane
B) Cytoplasm
C) Cell wall ✅
D) Nucleus
The rectangular shape is due to:
A) Cytoplasm
B) Cell wall ✅
C) Nucleus
D) Vacuole

🔹 Case Study 2

Seema observed cheek cells under a microscope. The cells were irregular in shape and had no cell wall.

Questions:

These cells belong to:
A) Plant
B) Animal ✅
C) Fungi
D) Bacteria
Which structure is absent?
A) Nucleus
B) Cytoplasm
C) Cell wall ✅
D) Membrane
Shape of these cells is:
A) Fixed
B) Rectangular
C) Irregular ✅
D) Square

🔹 Case Study 3

A student learned that mitochondria produce energy for the cell.

Questions:

Mitochondria is called:
A) Brain
B) Powerhouse ✅
C) Skin
D) Heart
Energy produced is in form of:
A) DNA
B) ATP ✅
C) Water
D) Protein

🔹 Case Study 4

Plants prepare their food using sunlight and chlorophyll.

Questions:

The organelle involved is:
A) Vacuole
B) Nucleus
C) Chloroplast ✅
D) Mitochondria
The process is:
A) Respiration
B) Photosynthesis ✅
C) Digestion
D) Excretion

🔹 Case Study 5

A cell allows only certain substances to pass through its boundary.

Questions:

This property is called:
A) Diffusion
B) Permeability
C) Selective permeability ✅
D) Osmosis
The structure is:
A) Cell membrane ✅
B) Nucleus
C) Cytoplasm
D) Vacuole

🔹 Case Study 6

Amoeba is a unicellular organism that performs all life functions.

Questions:

Amoeba has:
A) Many cells
B) One cell ✅
C) No cell
D) Two cells
Movement in Amoeba is by:
A) Cilia
B) Flagella
C) Pseudopodia ✅
D) Legs

🔹 Case Study 7

A plant cell has a large central vacuole.

Questions:

Function of vacuole:
A) Movement
B) Storage ✅
C) Respiration
D) Digestion
Vacuole is large in:
A) Animal cell
B) Plant cell ✅
C) Bacteria
D) Virus

🔹 Case Study 8

Cells divide to produce new cells.

Questions:

Cell division helps in:
A) Death
B) Growth ✅
C) Sleep
D) Rest
Identical cells are formed by:
A) Meiosis
B) Mitosis ✅
C) Fusion
D) Diffusion

🔹 Case Study 9

RBCs in humans do not have a nucleus.

Questions:

RBC stands for:
A) Red Blood Cell ✅
B) Round Body Cell
C) Rapid Blood Cell
D) None
RBC lacks:
A) Cytoplasm
B) Membrane
C) Nucleus ✅
D) Oxygen

🔹 Case Study 10

Cells contain genetic material that controls heredity.

Questions:

Genetic material is:
A) Protein
B) DNA ✅
C) Fat
D) Water
DNA is present in:
A) Cytoplasm
B) Nucleus ✅
C) Membrane
D) Vacuole

🔹 Case Study 11

Paramecium moves using tiny hair-like structures.

Questions:

These structures are:
A) Flagella
B) Pseudopodia
C) Cilia ✅
D) Wings
Paramecium is:
A) Multicellular
B) Unicellular ✅
C) Tissue
D) Organ

🔹 Case Study 12

The cell membrane is made of lipids and proteins.

Questions:

Function of membrane:
A) Control movement ✅
B) Produce energy
C) Store food
D) Make DNA
It is:
A) Fully permeable
B) Impermeable
C) Selectively permeable ✅
D) Rigid

🔹 Case Study 13

Chromosomes carry hereditary information.

Questions:

Chromosomes are made of:
A) DNA ✅
B) Fat
C) Water
D) Protein only
They are found in:
A) Cytoplasm
B) Nucleus ✅
C) Membrane
D) Vacuole

🔹 Case Study 14

A student observed that plant cells have chloroplasts but animal cells do not.

Questions:

Chloroplast helps in:
A) Respiration
B) Photosynthesis ✅
C) Movement
D) Storage
Chloroplast is absent in:
A) Plant
B) Animal ✅
C) Both
D) None

🔹 Case Study 15

Cells form tissues, tissues form organs.

Questions:

Tissue is:
A) Group of organs
B) Group of cells ✅
C) Group of systems
D) Group of atoms
Organs form:
A) Cells
B) Systems ✅
C) Molecules
D) Atoms

🔹 Case Study 16

Muscle cells contain more mitochondria.

Questions:

Reason:
A) Storage
B) More energy needed ✅
C) Movement less
D) Less activity
Mitochondria produce:
A) DNA
B) Energy ✅
C) Water
D) Fat

🔹 Case Study 17

Water moves through a membrane from high to low concentration.

Questions:

This process is:
A) Diffusion
B) Osmosis ✅
C) Respiration
D) Digestion
It involves movement of:
A) Food
B) Water ✅
C) Air
D) Minerals

🔹 Case Study 18

Cells are the smallest unit capable of life.

Questions:

Cells perform:
A) Only movement
B) All life functions ✅
C) Only respiration
D) Only digestion
Example of unicellular organism:
A) Dog
B) Human
C) Amoeba ✅
D) Tree

🔹 Case Study 19

Plant cells have a rigid outer covering.

Questions:

This is called:
A) Membrane
B) Cell wall ✅
C) Cytoplasm
D) Nucleus
Function:
A) Protection and support ✅
B) Movement
C) Digestion
D) Respiration

🔹 Case Study 20

Cells have a control center that regulates activities.

Questions:

This part is:
A) Cytoplasm
B) Nucleus ✅
C) Membrane
D) Vacuole
It contains:
A) Water
B) DNA ✅
C) Food
D) Air

✅ Final Tip

👉 In exams, case studies test:

Understanding of concepts
Application of knowledge
Identification of structures

Here are 20 Short Answer Questions and 20 Long Answer Questions from
📘 Class 8 Science Chapter 8 – Cell: Structure and Functions (CBSE)
(with clear answers for exam preparation)

✏️ 🔹 SHORT ANSWER QUESTIONS (1–20)

1. What is a cell?

Answer:
A cell is the basic structural and functional unit of life.

2. Who discovered the cell?

Answer:
The cell was discovered by Robert Hooke in 1665.

3. What is cytology?

Answer:
Cytology is the study of cells.

4. Name the three main parts of a cell.

Answer:

Cell membrane
Cytoplasm
Nucleus

5. What is the function of the cell membrane?

Answer:
It controls the entry and exit of substances and protects the cell.

6. What is cytoplasm?

Answer:
Cytoplasm is a jelly-like substance present inside the cell where organelles are found.

7. What is the function of the nucleus?

Answer:
The nucleus controls all activities of the cell and contains genetic material (DNA).

8. What are organelles?

Answer:
Organelles are small structures inside the cell that perform specific functions.

9. What is mitochondria?

Answer:
Mitochondria are called the powerhouse of the cell as they produce energy.

10. What is chloroplast?

Answer:
Chloroplast is a cell organelle that helps in photosynthesis and contains chlorophyll.

11. What is a vacuole?

Answer:
A vacuole is a storage sac that stores water, food, and waste.

12. What is diffusion?

Answer:
Diffusion is the movement of particles from higher concentration to lower concentration.

13. What is osmosis?

Answer:
Osmosis is the movement of water through a semi-permeable membrane.

14. What is a unicellular organism?

Answer:
An organism made up of a single cell is called unicellular.

15. Give one example of unicellular organism.

Answer:
Amoeba.

16. What is a multicellular organism?

Answer:
An organism made up of many cells is called multicellular.

17. What is a cell wall?

Answer:
A cell wall is a rigid outer layer found in plant cells that provides support and protection.

18. What is selective permeability?

Answer:
It means allowing only certain substances to pass through the membrane.

19. What are chromosomes?

Answer:
Chromosomes are structures in the nucleus that contain genetic information (DNA).

20. What is protoplasm?

Answer:
Protoplasm is the living part of the cell, consisting of cytoplasm and nucleus.

📝 🔹 LONG ANSWER QUESTIONS (1–20)

1. Explain the structure of a cell.

Answer:
A cell consists of three main parts:

Cell membrane – outer covering, controls entry/exit
Cytoplasm – jelly-like substance with organelles
Nucleus – control center with DNA
These parts work together to perform life functions.

2. Describe the functions of cell membrane.

Answer:

Protects the cell
Maintains shape
Controls movement of substances
Is selectively permeable

3. Explain the functions of nucleus.

Answer:

Controls all activities of the cell
Stores genetic material (DNA)
Helps in cell division and reproduction

4. Write differences between plant cell and animal cell.

Answer:

Feature	Plant Cell	Animal Cell
Cell wall	Present	Absent
Chloroplast	Present	Absent
Shape	Fixed	Irregular
Vacuole	Large	Small

5. Explain mitochondria in detail.

Answer:
Mitochondria are organelles that produce energy in the form of ATP through respiration. They are called the powerhouse of the cell and are essential for all activities.

6. Describe chloroplast and its function.

Answer:
Chloroplast is found in plant cells and contains chlorophyll. It helps in photosynthesis, converting sunlight into food.

7. Explain vacuole and its function.

Answer:
Vacuole stores water, nutrients, and waste. In plant cells, it is large and helps maintain shape.

8. What is cell division? Explain its types.

Answer:
Cell division is the process of forming new cells.

Mitosis – produces identical cells
Meiosis – produces reproductive cells

9. Explain diffusion and osmosis.

Answer:

Diffusion: Movement of particles from high to low concentration
Osmosis: Movement of water through a semi-permeable membrane

10. What are unicellular organisms? Give examples.

Answer:
Organisms made of one cell.
Examples: Amoeba, Paramecium

11. What are multicellular organisms?

Answer:
Organisms made of many cells with specialized functions, like humans and plants.

12. Explain levels of organization in organisms.

Answer:
Cells → Tissues → Organs → Organ systems → Organism

13. What are chromosomes and genes?

Answer:
Chromosomes are structures in the nucleus made of DNA. Genes are units of heredity present on chromosomes.

14. Explain the importance of cells.

Answer:

Basic unit of life
Perform life processes
Carry genetic information
Help in growth and reproduction

15. Why are cells called the building blocks of life?

Answer:
Because all living organisms are made up of cells, just like buildings are made of bricks.

16. Explain the shape and size of cells.

Answer:
Cells vary in shape and size depending on their function. For example, nerve cells are long, RBCs are round.

17. What is selective permeability? Explain with example.

Answer:
It allows only certain substances to pass. Example: Oxygen enters cell, waste exits.

18. Explain the structure of nucleus.

Answer:

Nuclear membrane
Nucleolus
Chromatin
It controls cell activities.

19. Write functions of cytoplasm.

Answer:

Holds organelles
Site of chemical reactions
Helps in transport

20. Explain the role of mitochondria in energy production.

Answer:
Mitochondria break down food using oxygen to release energy in the form of ATP, which is used for all cell activities.

✅ Final Exam Tip

👉 Focus on:

Definitions (cell, organelles)
Differences (plant vs animal)
Functions of organelles
Diagrams

Here is a CBSE Pattern 80 Marks Question Paper for
📘 Class 8 Science – Chapter 8: Cell: Structure and Functions

📝 Question Paper

Class: 8 | Subject: Science
Chapter: Cell – Structure and Functions
Time: 3 Hours | Maximum Marks: 80

🔹 Section A – MCQs (1 × 20 = 20 Marks)

Choose the correct option:

The basic unit of life is:
A) Tissue
B) Organ
C) Cell
D) System
Cell was discovered by:
A) Newton
B) Robert Hooke
C) Darwin
D) Mendel
The control center of the cell is:
A) Cytoplasm
B) Nucleus
C) Membrane
D) Vacuole
Cytoplasm is:
A) Solid
B) Gas
C) Jelly-like
D) Hard
Mitochondria is called:
A) Brain
B) Powerhouse
C) Skin
D) Bone
Chloroplast is found in:
A) Animal cells
B) Plant cells
C) Both
D) None
Cell membrane is:
A) Fully permeable
B) Impermeable
C) Selectively permeable
D) Hard
Vacuole is used for:
A) Movement
B) Storage
C) Digestion
D) Respiration
Amoeba is:
A) Multicellular
B) Unicellular
C) Tissue
D) Organ
DNA is found in:
A) Cytoplasm
B) Nucleus
C) Membrane
D) Vacuole

Shape of RBC is:
A) Rectangular
B) Round
C) Square
D) Triangle
Cell wall is present in:
A) Animal cell
B) Plant cell
C) Both
D) None
Diffusion is movement of:
A) Water
B) Particles from high to low
C) Oxygen only
D) Food
Osmosis involves movement of:
A) Food
B) Water
C) Air
D) Minerals
Chromosomes are found in:
A) Cytoplasm
B) Nucleus
C) Membrane
D) Vacuole

Paramecium moves by:
A) Flagella
B) Cilia
C) Pseudopodia
D) Legs
Cells form:
A) Organs
B) Tissues
C) Systems
D) Organism
Tissue forms:
A) Cells
B) Organs
C) Systems
D) Atoms
Largest cell is:
A) RBC
B) Bacteria
C) Ostrich egg
D) Virus
Study of cells is called:
A) Biology
B) Cytology
C) Zoology
D) Botany