The Cell: Where Life Actually Happens
Every living thing you can think of — a mango tree, a mosquito, your own body — is made of cells. Robert Hooke first saw them in 1665 when he looked at cork under a microscope and noticed tiny box-like structures. He called them “cells” because they reminded him of monks’ rooms (cellula in Latin). That name stuck, and now we know these tiny units are running every single function keeping you alive right now.
The cell is not just a bag of chemicals. It’s an organized system with specific parts doing specific jobs — much like how a school has classrooms, a library, a lab, and a principal’s office, each with a distinct role. Once you understand what each part does and why it exists, the whole chapter clicks into place.
For Class 8 CBSE, this chapter carries good weightage in the annual exam. Questions come in the form of diagrams (label the parts), match-the-columns, and short answers. So we’ll build both conceptual clarity and exam readiness together.
Key Terms and Definitions
Cell — the basic structural and functional unit of all living organisms. Coined by Robert Hooke, 1665.
Unicellular organism — an organism made of a single cell that performs all life functions. Examples: Amoeba, Paramecium, bacteria.
Multicellular organism — an organism made of many cells, each typically specialised for a specific function. Examples: humans, mango trees, earthworms.
Cell membrane (Plasma membrane) — the thin, flexible outer boundary of a cell. Controls what enters and leaves — it’s selectively permeable.
Cell wall — a rigid outer layer found in plant cells (and bacteria/fungi) but NOT in animal cells. Made of cellulose in plants. Provides shape and mechanical support.
Cytoplasm — the jelly-like fluid filling the cell between the membrane and the nucleus. Contains all the organelles.
Nucleus — the control centre of the cell. Contains DNA, which carries all genetic instructions.
Organelle — a specialised structure inside the cell with a specific function. (Think “tiny organ.”)
Vacuole — a membrane-bound storage sac in the cytoplasm. Plant cells have one large central vacuole; animal cells have small, temporary ones.
Chloroplast — found only in plant cells (and algae). Contains the green pigment chlorophyll, which traps sunlight for photosynthesis.
Cell organelles covered at Class 8 level: nucleus, vacuoles, cell membrane, cell wall (plants), chloroplasts (plants).
The Cell Structure: Part by Part
Cell Membrane
Every cell — plant or animal — has a cell membrane. Think of it as a security gate: it decides what gets in (nutrients, water) and what goes out (waste products). Because it allows some substances to pass and blocks others, we call it selectively permeable.
A simple way to remember this: the cell membrane is the bouncer of the cell. It’s always there, always checking.
Cell Wall (Plants Only)
Outside the cell membrane in plant cells, there’s an additional thick, rigid layer — the cell wall. It’s made of cellulose, a carbohydrate. This wall is what gives plants their structural strength. Without it, a tree couldn’t stand up.
Animal cells have NO cell wall. This is one of the most tested differences in Class 8 exams.
CBSE pattern: A very common question is: “Why do plant cells not burst when placed in water but animal cells do?” The answer links to the cell wall providing rigidity and support. Animal cells, lacking a wall, can swell and burst in hypotonic solutions.
Cytoplasm
The cytoplasm is the fluid “ground” of the cell. It’s mostly water with dissolved salts, sugars, and proteins. All cell organelles float in this fluid. Chemical reactions essential for life happen here constantly.
Nucleus
The nucleus is enclosed by a double membrane called the nuclear membrane (or nuclear envelope). Inside the nucleus, you’ll find:
- Chromatin — loosely arranged DNA-protein material. During cell division, chromatin condenses into chromosomes.
- Nucleolus — a dense region inside the nucleus involved in making ribosomes.
The nucleus stores the genetic information (DNA) that determines all your characteristics — eye colour, blood group, height potential, everything.
If the cell is a city, the nucleus is the municipality office — it has all the blueprints (DNA) and issues all instructions.
Vacuoles
Vacuoles store food, water, or waste materials.
- Plant cells: One large, permanent central vacuole that can occupy up to 90% of the cell’s volume. Filled with cell sap, it keeps the plant turgid (firm).
- Animal cells: Several small, temporary vacuoles. No central vacuole.
Some single-celled organisms like Amoeba have a special food vacuole (digests food) and a contractile vacuole (expels excess water).
Chloroplasts (Plants and Algae Only)
Chloroplasts are green because they contain chlorophyll. They capture light energy and use it to make food from CO₂ and water — this is photosynthesis. Chloroplasts are found only in the parts of the plant exposed to sunlight: mainly leaves, sometimes young green stems.
Plant Cell vs Animal Cell: The Key Comparison
This table is your best friend for board exams:
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell wall | Present (cellulose) | Absent |
| Cell membrane | Present | Present |
| Chloroplast | Present (in green parts) | Absent |
| Vacuole | Large central vacuole | Small, temporary |
| Shape | Fixed, regular | Irregular, flexible |
| Size | Generally larger | Generally smaller |
This table appears in almost every Class 8 annual exam — either as a “differentiate between” question (3 marks) or a fill-in-the-table format. Know at least 4 differences cold.
Types of Organisms: Unicellular vs Multicellular
Unicellular Organisms
A single cell does everything — eating, moving, reproducing, excreting. Examples:
- Amoeba: uses pseudopodia (false feet) to move and capture food
- Paramecium: uses cilia (hair-like structures) to move
- Bacteria: the smallest and most numerous cells on Earth
- Chlamydomonas: a unicellular green alga with chloroplasts
Multicellular Organisms
Cells are specialised — they divide labour. Muscle cells contract, nerve cells transmit signals, red blood cells carry oxygen. You can’t ask a red blood cell to digest food; that’s the intestinal cell’s job.
This specialisation allows multicellular organisms to grow larger and perform complex functions. But it also means each cell depends on other cells — total teamwork.
Worked Examples
Example 1 — Easy (CBSE Level)
Q: Name the structural and functional unit of life. Who discovered it?
The cell is the structural and functional unit of life. Robert Hooke discovered cells in 1665 when he observed cork under a compound microscope.
Example 2 — Easy (CBSE Level)
Q: Why is the nucleus called the control centre of the cell?
The nucleus contains DNA, which carries all genetic information and instructions for every cellular activity. It controls processes like growth, metabolism, and reproduction. If the nucleus is removed from a cell, the cell cannot survive for long — it loses its ability to direct its own functions.
Example 3 — Medium (CBSE Annual Exam Level)
Q: Rahul placed a plant cell in salty water. He observed that the cell membrane pulled away from the cell wall. Explain what happened and why.
When a plant cell is placed in salty (hypertonic) solution, water moves out of the vacuole and cytoplasm by osmosis — from a region of higher water concentration (inside the cell) to lower water concentration (outside). As the cell loses water, the cytoplasm shrinks and the cell membrane pulls away from the rigid cell wall. This is called plasmolysis. The cell wall stays intact because it’s rigid, but the inner contents (cytoplasm + membrane) contract.
Example 4 — Medium (CBSE / ICSE Level)
Q: Compare a cheek cell with an onion peel cell. List THREE differences you would observe under a microscope.
| Feature | Cheek Cell (Animal) | Onion Peel Cell (Plant) |
|---|---|---|
| Cell wall | Absent | Present |
| Chloroplast | Absent | Absent (onion is not green — stored in dark) |
| Vacuole | Small/absent | Large central vacuole |
| Shape | Irregular | Rectangular, fixed |
Note: Onion peel cells are a plant cell but have no chloroplasts because the onion bulb is underground — no sunlight, so no need for photosynthesis.
Many students write “onion cells have chloroplasts.” They do NOT. Onion is a non-green plant part. Only green plant parts have chloroplasts.
Example 5 — Harder (ICSE / Olympiad Level)
Q: A cell is described as follows: it has a cell wall, a large central vacuole, no chloroplasts, and irregular shape. Is this description consistent? Explain.
This description is NOT fully consistent. A cell with a cell wall and large central vacuole is a plant cell — these are plant cell features. However, plant cells generally have a regular (rectangular) shape, not irregular. Animal cells are irregular in shape but lack both cell wall and central vacuole.
The description could belong to a non-photosynthetic plant cell (like an onion bulb cell or root cell) — which would have a cell wall, large vacuole, no chloroplasts (since no sunlight reaches roots), but should still be regular in shape. The “irregular shape” part makes it inconsistent with any standard cell type at this level.
Exam-Specific Tips
CBSE Class 8
- Diagram questions carry 2-3 marks. Practice labelling a plant cell and an animal cell separately. Must-label parts: cell wall (plant only), cell membrane, cytoplasm, nucleus, vacuole, chloroplast (plant only).
- Marks distribution: Usually 1 mark for each difference in plant vs animal cell comparisons. Give at least 3 clear points.
- The practical-based question often references the Cheek Cell / Onion Cell experiment from NCERT Lab Activity. Know the steps and what you observe.
ICSE Class 8
ICSE goes a level deeper. You may be asked about the nuclear membrane, nucleolus, and chromatin. Know that chromosomes are made of DNA + protein, and they carry genes.
For ICSE, the question “What is the role of the nucleolus?” often appears. Answer: The nucleolus is involved in the synthesis of ribosomes, which are needed for protein production.
Science Olympiad (NSO/NSTSE)
Expect questions on why unicellular organisms can survive independently, osmosis across cell membranes (conceptual), and the evolutionary significance of cell specialisation in multicellular organisms.
Common Mistakes to Avoid
Mistake 1: Confusing cell wall with cell membrane. The cell membrane is present in ALL cells (plant and animal). The cell wall is present only in plant cells (and bacteria/fungi). Never say “animal cells have no cell membrane.”
Mistake 2: Saying all plant cells have chloroplasts. Only the green parts of plants have chloroplasts. Root cells, onion bulb cells, and potato cells have no chloroplasts. Chloroplasts need sunlight to function — underground or non-green parts don’t have them.
Mistake 3: Writing “nucleus contains chromosomes” always. The nucleus contains chromatin normally. Chromosomes (condensed chromatin) only appear during cell division. In a resting cell, you see the nucleolus and chromatin — not distinct chromosomes.
Mistake 4: Saying vacuoles are absent in animal cells. Animal cells DO have vacuoles — they are just small and temporary. The large, permanent central vacuole is the plant cell feature. Amoeba has food vacuoles and contractile vacuoles.
Mistake 5: Incorrect statement about cell size. The statement “all cells are the same size” is wrong. Cells vary enormously — from bacteria (1-10 micrometres) to a human nerve cell that can be over a metre long (from spinal cord to toe). Size depends on function.
Practice Questions
Q1. Name the scientist who first observed cells and the instrument he used.
Robert Hooke first observed cells in 1665 using a compound microscope. He observed cork (dead plant cells) and described the small box-like compartments as “cells.”
Q2. State ONE function each of: (a) cell membrane (b) nucleus (c) vacuole (d) chloroplast
(a) Cell membrane — controls the entry and exit of substances (selectively permeable) (b) Nucleus — controls all cellular activities; contains DNA (c) Vacuole — stores water, food, or waste; maintains cell turgidity in plants (d) Chloroplast — traps sunlight and performs photosynthesis; contains chlorophyll
Q3. Give two differences between unicellular and multicellular organisms with one example each.
| Feature | Unicellular | Multicellular |
|---|---|---|
| Number of cells | Single cell | Many cells |
| Division of labour | One cell does all functions | Cells are specialised |
| Example | Amoeba, Paramecium | Human, mango tree |
Q4. Why does a plant cell not burst when placed in pure water but an animal cell does?
When placed in pure water, both cells absorb water by osmosis (water enters the cell). In a plant cell, the rigid cell wall resists the swelling and prevents the cell from bursting. In an animal cell, there is no cell wall — so as water keeps entering, the cell membrane stretches and eventually bursts (lysis).
Q5. An organism can make its own food and is made of a single cell. Name the likely organism and explain how it makes food.
The organism is likely Chlamydomonas (or Euglena), a unicellular alga. It contains chloroplasts with chlorophyll, which trap sunlight. Using this light energy, CO₂ from water/air, and water, it performs photosynthesis to produce glucose and oxygen.
Q6. What would happen to a plant if all chloroplasts were removed from its cells?
The plant would be unable to perform photosynthesis — it could not produce its own food. Without glucose, the plant would starve, growth would stop, and eventually the plant would die. The plant would have to depend entirely on external sources, which is not possible for a non-parasitic plant.
Q7. Draw and label a plant cell with at least 5 structures. (Describe what your diagram should show)
Your diagram should show:
- Cell wall — outermost thick layer
- Cell membrane — thin layer just inside the cell wall
- Cytoplasm — fluid filling the cell
- Nucleus — round structure near centre, with nuclear membrane visible
- Central vacuole — large, taking up most of the cell space
- Chloroplasts — oval green structures in the cytoplasm (draw 2-3)
Use a rectangular outline for the plant cell shape. Label each part with arrows.
Q8. The nucleus of a cell is removed in a lab experiment. Predict what will happen to the cell over the next few days and explain why.
Without a nucleus, the cell cannot survive for long. The nucleus contains DNA, which carries instructions for making proteins and controlling all metabolic activities. Without these instructions:
- The cell cannot repair itself
- It cannot reproduce
- It cannot regulate its functions properly
The cell will eventually die. This proves that the nucleus is the control centre — essential for the cell’s continued survival. (This is actually demonstrated in experiments with Amoeba — enucleated Amoeba cannot survive.)
FAQs
Why are cells so small?
Cells need to exchange materials (nutrients, waste, oxygen) through their surface. If a cell gets too large, the volume grows faster than the surface area — not enough surface to serve the interior. Small size maintains a favourable surface area to volume ratio, allowing efficient exchange. That’s why most cells are microscopic.
What is the difference between cell wall and cell membrane?
The cell membrane is a thin, flexible, selectively permeable layer present in all cells. The cell wall is a thick, rigid, non-living layer made of cellulose, found only outside the cell membrane in plant cells. They are different structures with different compositions and functions.
Do all cells have a nucleus?
No. Cells with a well-defined nucleus enclosed in a nuclear membrane are called eukaryotic cells (plants, animals, fungi). Bacteria have DNA but no nuclear membrane — they are called prokaryotic cells. At Class 8, we primarily study eukaryotic cells, but bacteria are the main example of prokaryotes.
Why do onion cells have no chloroplasts?
The onion bulb is an underground storage organ. Since it receives no sunlight, there’s no need for photosynthesis — and therefore no chloroplasts. Chloroplasts develop only in cells that are exposed to light. If you grow an onion sprout in sunlight, the green parts that emerge WILL have chloroplasts.
What is the largest cell in the human body?
The female egg cell (ovum) is the largest cell in the human body — just barely visible to the naked eye at about 0.1 mm. The longest cell is the nerve cell (neuron), which can stretch from the spinal cord to the tips of your toes.
How is a cell different from an atom?
An atom is the smallest unit of matter (chemistry). A cell is the smallest unit of life (biology). A single cell contains millions of atoms and molecules organised into complex structures. All living things are made of cells; not all matter is made of cells.
What does “selectively permeable” mean?
It means the membrane allows certain substances to pass through freely (like water, oxygen, glucose) while blocking others (large molecules, harmful substances). This selectivity is critical — it’s how the cell controls its internal environment. Think of it as a filter, not just a wrapper.