🧬 CELL — COMPLETE CLASS 8–10 NOTES
1. What is a Cell?
A cell is the basic structural and functional unit of life.
- All living organisms are made up of cells.
- A cell performs various life processes such as nutrition, respiration, excretion and reproduction.
- Some organisms consist of only one cell, while others contain millions or trillions of cells.
Examples:
- Amoeba → unicellular organism
- Human → multicellular organism
- Bacteria → unicellular organism
2. Discovery of the Cell
Robert Hooke discovered cells in 1665 while observing a thin slice of cork under a microscope.
He observed many small box-like compartments and called them cells.
Important Scientists
| Scientist | Contribution |
|---|---|
| Robert Hooke | Discovered cells in cork |
| Anton van Leeuwenhoek | First observed living cells |
| Robert Brown | Discovered nucleus |
| Schleiden | Plants are made of cells |
| Schwann | Animals are made of cells |
| Virchow | New cells arise from pre-existing cells |
3. Cell Theory
The modern cell theory states:
- All living organisms are made up of one or more cells.
- The cell is the basic structural and functional unit of life.
- All cells arise from pre-existing cells.
4. Types of Organisms
Unicellular Organisms
Organisms made up of one cell.
Examples:
- Amoeba
- Paramecium
- Bacteria
- Yeast
Multicellular Organisms
Organisms made up of many cells.
Examples:
- Humans
- Plants
- Dogs
- Birds
5. Main Parts of a Cell
A typical cell contains:
- Cell membrane
- Cytoplasm
- Nucleus
- Cell organelles
Plant cells additionally have:
- Cell wall
- Chloroplast
- Large central vacuole
6. Cell Membrane
The cell membrane is the thin outer covering of the cell.
Functions
- Protects the cell.
- Gives shape to the cell.
- Controls movement of substances into and out of the cell.
- It is selectively permeable.
Example
Oxygen and carbon dioxide can pass through the cell membrane.
7. Cell Wall
The cell wall is present in plant cells but absent in animal cells.
It is mainly made of cellulose.
Functions
- Provides support.
- Gives shape.
- Protects the cell.
- Prevents the plant cell from bursting when excess water enters.
8. Cytoplasm
The cytoplasm is the jelly-like substance present between the cell membrane and nucleus.
It contains various cell organelles.
Functions
- Site of many chemical reactions.
- Holds cell organelles in position.
9. Nucleus
The nucleus is usually called the control centre of the cell.
It contains genetic material called DNA.
Functions
- Controls cell activities.
- Contains chromosomes.
- Transfers hereditary information.
- Helps in cell division.
Nucleus contains:
Nuclear membrane → Nucleoplasm → Nucleolus → Chromatin/Chromosomes
10. Chromosomes
Chromosomes are thread-like structures present inside the nucleus.
They contain DNA.
DNA carries genes, which determine inherited characteristics.
DNA → Genes → Hereditary information
11. Mitochondria
Mitochondria are known as the powerhouses of the cell.
They release energy from food during cellular respiration.
Equation
Glucose + Oxygen → Carbon dioxide + Water + Energy
The usable energy is stored mainly in the form of ATP.
12. Ribosomes
Ribosomes are tiny structures responsible for protein synthesis.
Therefore:
Ribosome → Protein synthesis
They may be present freely in the cytoplasm or attached to rough endoplasmic reticulum.
13. Endoplasmic Reticulum
The endoplasmic reticulum (ER) is a network of membranes inside the cell.
There are two types:
Rough ER
Contains ribosomes.
Function: Protein synthesis and transport.
Smooth ER
Does not contain ribosomes.
Functions:
- Lipid synthesis
- Detoxification
- Helps in carbohydrate metabolism
14. Golgi Apparatus
The Golgi apparatus consists of flattened membrane-bound sacs.
Functions
- Modifies proteins and lipids.
- Packages substances.
- Helps in secretion.
- Forms lysosomes.
Think of it as the cell's packaging and dispatch centre.
15. Lysosomes
Lysosomes are small membrane-bound organelles containing digestive enzymes.
They are sometimes called suicidal bags of the cell.
Functions
- Digest waste materials.
- Destroy damaged organelles.
- Help destroy foreign particles.
- Participate in intracellular digestion.
16. Vacuoles
Vacuoles are storage structures surrounded by a membrane.
Plant cells
Usually have a large central vacuole.
Animal cells
Usually have small temporary vacuoles.
They can store:
- Water
- Food
- Minerals
- Waste products
- Pigments
17. Plastids
Plastids are mainly found in plant cells.
Three important types are:
Chloroplasts
Contain chlorophyll and perform photosynthesis.
Chromoplasts
Contain pigments that give colour to flowers and fruits.
Leucoplasts
Usually colourless and mainly involved in storage.
18. Chloroplast
The chloroplast is the site of photosynthesis.
It contains chlorophyll.
Photosynthesis
Carbon dioxide + Water → Glucose + Oxygen
Light energy and chlorophyll are required.
19. Centrosome
The centrosome is generally present in animal cells.
It plays an important role in cell division by helping in the formation of spindle fibres.
20. Prokaryotic Cell
A prokaryotic cell does not have a true membrane-bound nucleus.
Examples:
- Bacteria
- Cyanobacteria
Features
- No true nucleus
- DNA lies in the nucleoid region
- Usually smaller and simpler
- Membrane-bound organelles are generally absent
21. Eukaryotic Cell
A eukaryotic cell has a well-defined nucleus surrounded by a nuclear membrane.
Examples:
- Plant cells
- Animal cells
- Fungi
- Protists
22. Prokaryotic vs Eukaryotic Cells
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | No true nucleus | True nucleus |
| Size | Generally smaller | Generally larger |
| Membrane-bound organelles | Generally absent | Present |
| DNA | Nucleoid region | Nucleus |
| Example | Bacteria | Plants, animals |
23. Plant Cell
A plant cell generally contains:
- Cell wall
- Cell membrane
- Cytoplasm
- Nucleus
- Chloroplast
- Large vacuole
- Mitochondria
- ER
- Golgi apparatus
- Ribosomes
24. Animal Cell
An animal cell generally contains:
- Cell membrane
- Cytoplasm
- Nucleus
- Mitochondria
- Ribosomes
- ER
- Golgi apparatus
- Lysosomes
- Small vacuoles
- Centrosome
25. Plant Cell vs Animal Cell
| Plant Cell | Animal Cell |
|---|---|
| Cell wall present | Cell wall absent |
| Chloroplasts usually present | Chloroplasts absent |
| Large central vacuole | Small vacuoles |
| Usually fixed/regular shape | Usually flexible/irregular shape |
| Centrosome generally absent in higher plants | Centrosome present |
| Stores starch | Stores glycogen |
26. Cell Organelles — Quick Revision
| Organelle | Main Function |
|---|---|
| Cell membrane | Controls entry and exit |
| Cell wall | Support and protection |
| Nucleus | Control centre |
| Mitochondria | Energy production |
| Ribosome | Protein synthesis |
| ER | Transport/synthesis |
| Golgi apparatus | Packaging and secretion |
| Lysosome | Digestion |
| Vacuole | Storage |
| Chloroplast | Photosynthesis |
| Chromoplast | Colour |
| Leucoplast | Storage |
| Centrosome | Cell division |
27. Diffusion
Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration.
Example
Oxygen moves from the blood into cells by diffusion.
28. Osmosis
Osmosis is the movement of water molecules through a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.
Example
Water enters plant root cells from the soil through osmosis.
29. Hypotonic Solution
A hypotonic solution has relatively more water outside the cell.
Water enters the cell.
Cell → swells
30. Hypertonic Solution
A hypertonic solution has relatively less water outside the cell.
Water moves out of the cell.
Cell → shrinks
In plant cells, this can cause plasmolysis.
31. Isotonic Solution
An isotonic solution has approximately equal water concentration inside and outside the cell.
There is no net movement of water.
32. Plasmolysis
Plasmolysis is the shrinkage of the cell contents away from the cell wall when a plant cell loses water in a hypertonic solution.
33. Cell Division
Cell division is the process by which a parent cell divides to form new cells.
Two major types:
Mitosis
Produces genetically similar daughter cells and is important for growth and repair.
Meiosis
Produces reproductive cells and reduces chromosome number by half.
34. Mitosis
Mitosis generally produces two daughter cells.
Importance:
- Growth
- Repair
- Replacement of damaged cells
- Asexual reproduction in some organisms
35. Meiosis
Meiosis is a special type of cell division involved in the formation of gametes.
It reduces the chromosome number by half.
Example:
In humans:
46 chromosomes → 23 chromosomes
36. Cell Differentiation
Cell differentiation is the process by which cells become specialized for particular functions.
Examples:
- Nerve cells → transmit impulses
- Muscle cells → contraction
- Red blood cells → transport oxygen
- Root hair cells → absorb water and minerals
37. Tissue
A tissue is a group of similar cells performing a specific function.
Examples:
- Muscle tissue
- Nervous tissue
- Xylem
- Phloem
Organization
Cell → Tissue → Organ → Organ system → Organism
38. Surface Area to Volume Ratio
Small cells have a relatively large surface area compared with their volume.
This helps them efficiently exchange:
- Oxygen
- Nutrients
- Waste products
This is one reason cells generally remain microscopic.
39. Why Are Cells Small?
Cells are generally small because a smaller cell can exchange materials more efficiently with its surroundings.
As a cell becomes very large, its surface-area-to-volume ratio decreases.
40. Cell Shape
Cells have different shapes depending on their functions.
Examples:
- RBC → biconcave
- Nerve cell → long and branched
- Muscle cell → elongated
- Root hair cell → long projection
41. Specialised Cells
Red Blood Cell
Function: Transport oxygen.
Nerve Cell
Function: Carry nerve impulses.
Muscle Cell
Function: Contraction and movement.
Root Hair Cell
Function: Absorption of water and minerals.
42. Important Cell Diagrams
For exams, practise drawing and labelling:
- Plant cell
- Animal cell
- Prokaryotic cell
- Nucleus
- Mitochondrion
- Chloroplast
- Osmosis experiment
- Plasmolysed cell
43. Important Differences
Cell Wall vs Cell Membrane
| Cell Wall | Cell Membrane |
|---|---|
| Non-living structure | Living membrane |
| Present in plants | Present in plants and animals |
| Mainly cellulose in plants | Mainly lipids and proteins |
| Provides rigidity | Controls movement |
Cell vs Tissue
Cell: Basic unit of life.
Tissue: Group of similar cells performing a particular function.
44. Important Definitions
Cell: Basic structural and functional unit of life.
Nucleus: Control centre containing genetic material.
Cytoplasm: Jelly-like substance containing organelles.
Organelle: Specialized structure inside a cell.
Diffusion: Movement from higher to lower concentration.
Osmosis: Movement of water through a selectively permeable membrane.
Tissue: Group of similar cells performing a particular function.
Plasmolysis: Shrinkage of cell contents due to water loss.
45. Very Important One-Liners
- Powerhouse of cell: Mitochondria
- Control centre: Nucleus
- Protein synthesis: Ribosomes
- Photosynthesis: Chloroplast
- Packaging centre: Golgi apparatus
- Suicidal bags: Lysosomes
- Storage: Vacuole
- Plant cell wall: Cellulose
- Genetic material: DNA
- Basic unit of life: Cell
- Cell discovered by: Robert Hooke
- Living cells first observed by: Leeuwenhoek
- True nucleus absent in: Prokaryotes
- True nucleus present in: Eukaryotes
46. Important MCQs
Q1. The basic unit of life is:
A. Tissue
B. Organ
C. Cell
D. Organ system
Answer: C. Cell
Q2. Which organelle is called the powerhouse?
A. Ribosome
B. Mitochondria
C. Nucleus
D. Golgi apparatus
Answer: B. Mitochondria
Q3. Photosynthesis takes place in:
A. Lysosome
B. Mitochondria
C. Chloroplast
D. Ribosome
Answer: C. Chloroplast
Q4. Which organelle controls cell activities?
A. Nucleus
B. Vacuole
C. Ribosome
D. Cell wall
Answer: A. Nucleus
Q5. Which structure is present in plant cells but absent in animal cells?
A. Cell membrane
B. Cytoplasm
C. Cell wall
D. Nucleus
Answer: C. Cell wall
47. Assertion–Reason
Assertion:
Mitochondria are called the powerhouse of the cell.
Reason:
They release usable energy during cellular respiration.
Answer: Both statements are correct, and the reason explains the assertion.
48. Short Answer Questions
Q1. Why is the nucleus called the control centre?
Because it contains genetic material and controls many activities of the cell.
Q2. Why are mitochondria called the powerhouse?
Because they release energy from food during cellular respiration.
Q3. What is the function of chloroplast?
It carries out photosynthesis.
Q4. What is osmosis?
It is the movement of water through a selectively permeable membrane from higher water concentration to lower water concentration.
Q5. Why do plant cells have a cell wall?
It provides strength, support and protection.
49. HOTS Questions
Q1. What would happen if mitochondria stopped functioning?
The cell would produce much less usable energy, severely affecting energy-requiring processes.
Q2. Why does an onion peel cell have a definite shape?
Because its cell wall provides rigidity and support.
Q3. Why do root hair cells have long extensions?
The extensions increase surface area and help absorb water and minerals efficiently.
50. Diagram Labelling Practice
Plant Cell
Label:
Cell wall → Cell membrane → Cytoplasm → Nucleus → Chloroplast → Vacuole → Mitochondria → Golgi apparatus → ER → Ribosomes
Animal Cell
Label:
Cell membrane → Cytoplasm → Nucleus → Mitochondria → Golgi apparatus → ER → Ribosomes → Lysosome → Centrosome
51. Exam-Focused Questions
2 Marks
- Define cell.
- What is osmosis?
- Name two cell organelles.
- What is the function of mitochondria?
- Differentiate between diffusion and osmosis.
3 Marks
- Explain the functions of nucleus.
- Compare plant and animal cells.
- Explain the structure and function of mitochondria.
- Describe prokaryotic and eukaryotic cells.
5 Marks
- Draw and label a plant cell.
- Draw and label an animal cell.
- Explain the functions of major cell organelles.
- Explain osmosis with an experiment.
- Differentiate between plant and animal cells.
52. Super Revision Chart
CELL
↓
Cell Membrane → Protection + transport
Cytoplasm → Chemical reactions
Nucleus → Control + DNA
Mitochondria → Energy
Ribosomes → Protein
ER → Synthesis + transport
Golgi → Packaging
Lysosomes → Digestion
Vacuole → Storage
Chloroplast → Photosynthesis
Cell Wall → Support
53. ⭐ Must Learn for DAV/CBSE Exams
Before the exam, make sure you can:
✅ Draw plant cell with labels
✅ Draw animal cell with labels
✅ Draw prokaryotic cell
✅ Explain all major cell organelles
✅ Differentiate plant and animal cells
✅ Differentiate prokaryotic and eukaryotic cells
✅ Explain diffusion and osmosis
✅ Explain plasmolysis
✅ Learn cell theory
✅ Learn scientists and their discoveries
✅ Understand mitosis and meiosis
✅ Know specialised cells
✅ Practise MCQs + assertion-reason + diagram questions
🧬 CELL — ADVANCED & COMPLETE NOTES
Let’s go deeper into Cell with structure, organelles, diagrams, experiments, higher-order questions, and important exam points.
54. Structure of a Typical Cell
A cell can be broadly divided into:
1. Cell envelope
- Cell wall
- Cell membrane
2. Cytoplasm
- Cytosol
- Cell organelles
3. Nucleus
- Nuclear membrane
- Nucleoplasm
- Nucleolus
- Chromatin
Basic arrangement
Cell wall → Cell membrane → Cytoplasm → Nucleus + Organelles
55. Cell Envelope
The cell envelope refers to the protective boundary around a cell.
In plant cells:
Cell wall + Cell membrane
In animal cells:
Cell membrane only
The cell membrane regulates what enters and leaves the cell.
56. Plasma Membrane
The plasma membrane is also called the cell membrane.
It is made mainly of lipids and proteins.
Important property
It is selectively permeable.
This means that it allows some substances to pass through while restricting others.
Example
Oxygen can enter the cell, while some large molecules cannot freely cross the membrane.
57. Cell Wall — Detailed
Plant cell walls are mainly composed of cellulose.
The cell wall is:
- Rigid
- Strong
- Non-living
- Freely permeable to many small substances
Functions
- Gives mechanical strength.
- Maintains cell shape.
- Protects the cell.
- Prevents excessive expansion.
58. Cytosol vs Cytoplasm
These two terms are sometimes confused.
Cytosol
The fluid portion of the cell.
Cytoplasm
Cytosol + cell organelles outside the nucleus.
So:
Cytoplasm = Cytosol + Organelles
59. Nucleus — Detailed Structure
The nucleus has:
Nuclear envelope
A double membrane surrounding the nucleus.
Nuclear pores
Allow movement of certain substances between nucleus and cytoplasm.
Nucleoplasm
Fluid inside the nucleus.
Nucleolus
Region involved in production of ribosomal components.
Chromatin
DNA associated with proteins.
During cell division, chromatin becomes highly condensed into chromosomes.
60. Gene → DNA → Chromosome
Remember this relationship:
DNA contains hereditary information.
A gene is a functional segment of DNA.
DNA is packaged with proteins to form chromatin, which becomes condensed into chromosomes during cell division.
Simple chain
Gene → DNA → Chromatin → Chromosome
More accurately, genes are segments of DNA located on chromosomes.
61. Mitochondria — Detailed
Mitochondria have a double membrane.
Outer membrane
Smooth outer boundary.
Inner membrane
Highly folded to form structures called cristae.
Matrix
Inner fluid-filled region.
The folds increase the surface area available for cellular respiration.
Important point
Mitochondria contain their own DNA and ribosomes.
62. Why Are Cristae Important?
The inner membrane of mitochondria is folded into cristae.
These folds:
increase surface area → more sites for energy-releasing reactions
Therefore, cristae are important for efficient cellular respiration.
63. Chloroplast — Detailed
Chloroplasts are found mainly in green plant cells.
They contain chlorophyll.
Main structures:
- Outer membrane
- Inner membrane
- Stroma
- Thylakoids
- Grana
Grana
Stacks of thylakoids.
Stroma
Fluid region surrounding the grana.
64. Chlorophyll
Chlorophyll is the green pigment responsible for absorbing light energy during photosynthesis.
It enables plants to convert light energy into chemical energy.
Photosynthesis
CO₂ + H₂O → Glucose + O₂
Light and chlorophyll are required.
65. Mitochondria vs Chloroplast
| Mitochondria | Chloroplast |
|---|---|
| Cellular respiration | Photosynthesis |
| Releases usable energy | Captures light energy |
| Found in plant and animal cells | Mainly in plant/algal cells |
| Has cristae | Has grana |
| Contains its own DNA | Contains its own DNA |
66. Endoplasmic Reticulum — Detailed
The ER forms an interconnected membrane network.
Rough ER
Rough appearance → ribosomes attached
Mainly involved in:
- Protein synthesis
- Protein transport
Smooth ER
Smooth appearance → no ribosomes
Functions:
- Lipid synthesis
- Detoxification
- Metabolism of carbohydrates
67. Golgi Apparatus — Detailed
The Golgi apparatus is composed of flattened membrane-bound sacs.
It performs:
Receive → Modify → Sort → Package → Transport
Example
A protein produced by rough ER can be modified and packaged by the Golgi apparatus.
68. Lysosome — Detailed
Lysosomes contain digestive enzymes.
They can break down:
- Worn-out cell parts
- Food particles
- Foreign materials
- Cellular waste
They help maintain cellular cleanliness.
69. Vacuole — Detailed
A vacuole is surrounded by a membrane called the tonoplast in plant cells.
The large plant vacuole contains cell sap.
Cell sap may contain:
- Water
- Sugars
- Salts
- Pigments
- Waste products
Importance
The large vacuole helps maintain turgor pressure, which contributes to the firmness of plant tissues.
70. Plastids — Detailed Classification
1. Chloroplast
Green pigment → photosynthesis.
2. Chromoplast
Other pigments → colour of flowers and fruits.
3. Leucoplast
Colourless → storage.
Examples of stored substances include:
- Starch
- Oils
- Proteins
71. Cell Organelles with Double Membranes
Important double-membrane organelles include:
- Nucleus
- Mitochondria
- Chloroplasts
Single-membrane organelles
Examples:
- Endoplasmic reticulum
- Golgi apparatus
- Lysosomes
- Vacuoles
Non-membranous structures
Examples:
- Ribosomes
- Cytoskeleton
- Centrosome/centrioles
72. Semi-Autonomous Organelles
Mitochondria and chloroplasts are often described as semi-autonomous organelles because they contain:
- Their own DNA
- Their own ribosomes
- Machinery for producing some of their proteins
However, they still depend heavily on nuclear genes and the rest of the cell.
73. Cytoskeleton
The cytoskeleton is a network of protein fibres inside cells.
It helps with:
- Cell shape
- Internal organization
- Movement
- Transport of materials
- Cell division
Major components include:
- Microtubules
- Microfilaments
- Intermediate filaments
74. Centrosome and Centrioles
Animal cells commonly contain a centrosome containing a pair of centrioles.
They participate in the organization of microtubules and are important during cell division.
75. Cilia and Flagella
Cilia
Short, numerous projections.
Function:
Movement of cell or substances across the cell surface
Flagellum
Usually longer and fewer in number.
Function:
Movement
Example
Human sperm cell has a flagellum that helps it move.
76. Cell Movement
Cells can move using specialized structures.
Examples:
Amoeba → pseudopodia
Sperm → flagellum
Paramecium → cilia
77. Amoeba and Pseudopodia
Amoeba forms temporary projections called pseudopodia.
"Pseudopodia" means false feet.
They help in:
- Movement
- Capturing food
78. Diffusion — Detailed Example
Suppose perfume is sprayed in one corner of a room.
Initially:
Perfume concentration = high near spray
Molecules move randomly and spread throughout the room.
Eventually:
Concentration becomes more uniform.
This illustrates diffusion.
79. Osmosis Experiment — Potato
Materials
- Potato
- Salt/sugar
- Water
- Plate/container
Procedure
- Cut a potato.
- Make a small cavity.
- Put concentrated salt/sugar solution in the cavity.
- Place the potato in water.
- Observe after some time.
Water moves toward the concentrated solution through the potato tissues.
Conclusion
Water movement through a selectively permeable membrane is osmosis.
80. Raisin Experiment
Dry raisins are placed in water.
After some time:
Raisins swell.
Why?
Water enters the raisin cells by osmosis.
If swollen raisins are placed in concentrated sugar solution, water can move out and the raisins shrink.
81. Plasmolysis Experiment
Take an onion peel and place it in a concentrated salt solution.
Water leaves the cells.
The cell membrane and cytoplasm shrink away from the cell wall.
This is called:
Plasmolysis
82. Deplasmolysis
If a plasmolysed plant cell is placed in water, water enters the cell by osmosis.
The cell can regain its original condition.
This is called deplasmolysis.
83. Turgidity
When a plant cell absorbs water, it becomes firm or turgid.
Turgidity helps plants maintain rigidity.
This is particularly important in non-woody plant tissues.
84. Flaccidity
When plant cells lose water and become less firm, they become flaccid.
Excessive water loss can cause plants to wilt.
85. Endocytosis
Endocytosis is the process by which a cell takes materials into the cell by forming a membrane-bound vesicle.
Example
Amoeba can engulf food by forming a food vacuole.
86. Exocytosis
Exocytosis is the process by which materials are released outside the cell through vesicles that fuse with the cell membrane.
Examples include secretion of:
- Certain hormones
- Enzymes
- Neurotransmitters
87. Cell Nutrition
Cells require nutrients such as:
- Carbohydrates
- Proteins
- Lipids
- Vitamins
- Minerals
- Water
These support:
Energy + Growth + Repair + Maintenance
88. Cellular Respiration
Cellular respiration releases usable energy from food.
Aerobic respiration
Uses oxygen.
Glucose + Oxygen → Carbon dioxide + Water + Energy
Anaerobic respiration
Occurs without oxygen in certain conditions.
For example, yeast can produce:
Glucose → Alcohol + CO₂ + Energy
89. Cell Cycle
The cell cycle is the sequence of events through which a cell grows and divides.
Broadly:
Interphase → Cell division → Daughter cells
Interphase includes:
- G₁ phase
- S phase
- G₂ phase
S phase
DNA is replicated.
90. Mitosis — Stages
The major stages are:
Prophase → Metaphase → Anaphase → Telophase
Remember:
PMAT
P → Prophase
M → Metaphase
A → Anaphase
T → Telophase
Cytokinesis generally follows or overlaps with the end of mitosis.
91. Prophase
During prophase:
- Chromatin condenses into chromosomes.
- Nuclear envelope begins to break down.
- Spindle apparatus develops.
92. Metaphase
Chromosomes line up near the equator of the cell.
93. Anaphase
Sister chromatids separate and move toward opposite poles.
94. Telophase
Chromosomes reach opposite poles.
New nuclear envelopes form around the chromosome sets.
95. Cytokinesis
Cytokinesis is the division of the cytoplasm to produce separate daughter cells.
Animal cells
Usually form a cleavage furrow.
Plant cells
Usually form a cell plate.
96. Mitosis vs Meiosis
| Mitosis | Meiosis |
|---|---|
| Usually one division | Two successive divisions |
| Produces 2 daughter cells | Usually produces 4 daughter cells |
| Chromosome number maintained | Chromosome number halved |
| Growth and repair | Gamete formation |
| Daughter cells generally genetically similar | Daughter cells genetically varied |
97. Why Is Cell Division Important?
Cell division is essential for:
- Growth
- Repair
- Replacement
- Reproduction
- Development
- Formation of gametes
98. Stem Cells
Stem cells are cells that can:
- Self-renew.
- Differentiate into specialized cell types under appropriate conditions.
They are important in growth, development and tissue repair.
99. Cell Communication
Cells communicate with one another using chemical signals.
Examples include:
- Hormones
- Neurotransmitters
- Local signalling molecules
Cell communication helps coordinate activities throughout multicellular organisms.
100. ⭐ MASTER REVISION TABLE
| Structure | Remember As |
|---|---|
| Cell membrane | Gatekeeper |
| Cell wall | Support |
| Nucleus | Control centre |
| DNA | Genetic information |
| Ribosome | Protein factory |
| Mitochondria | Powerhouse |
| Chloroplast | Solar/food factory |
| ER | Transport network |
| Golgi | Packaging centre |
| Lysosome | Digestive system |
| Vacuole | Storage tank |
| Centrosome | Cell division organizer |
| Cilia | Short movement structures |
| Flagellum | Long movement structure |
🔥 Most Important Diagrams to Practise
- Plant cell — fully labelled
- Animal cell — fully labelled
- Prokaryotic cell
- Mitochondrion
- Chloroplast
- Nucleus
- Osmosis experiment
- Plasmolysis
- Mitosis — PMAT
- Plant cell vs animal cell
These additional sections take the chapter beyond basic definitions and cover the diagram, experiment, application, and higher-order areas that are especially useful for DAV/CBSE-style preparation.
