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Every cell has smaller parts inside it. Some parts are in all cells. A few parts are only in plant cells. We will look at each one.
Cell Membrane
- A thin skin covers every cell.
- It holds the cytoplasm and nucleus in.
- It has tiny pores, so it is porous.
- It controls what enters and leaves.
Example 1 — Food Entering a Cell
- Glucose and oxygen are needed by the cell.
- They pass in through the pores of the cell membrane.
- So the membrane lets useful things enter.
Example 2 — Waste Leaving a Cell
- Carbon dioxide is a waste made in the cell.
- It goes out through the pores of the membrane.
- So the membrane also lets waste leave.
Important Points
- It is selectively permeable — it chooses what passes through.
- Also called the plasma membrane; both names mean the same thing.
- Unlike the cell wall, the membrane is a living part of the cell.
Definition — Cell Membrane
The thin porous skin around a cell that controls the movement of things into and out of the cell.
Protoplasm
- Protoplasm is all the living matter inside.
- It lies within the cell membrane.
- It includes cytoplasm, nucleus and organelles.
- Mostly carbon, hydrogen, nitrogen and oxygen.
Example 1 — Inside an Onion Cell
- An onion peel cell has jelly-like matter inside.
- This living matter is its protoplasm.
- The cytoplasm and nucleus together make it up.
Example 2 — Stored Substances
- Protoplasm holds water, proteins, fats and salts.
- It also has carbohydrates and nucleic acids.
- So protoplasm is the living material that keeps the cell working.
Important Points
- Protoplasm was once called "the physical basis of life".
- Cytoplasm + nucleus together is the easy way to remember it.
- Trap: the cell wall is non-living, so it is not part of protoplasm.
Definition — Protoplasm
All the living matter inside a cell, made up of cytoplasm, nucleus and other organelles.
Cytoplasm
- Cytoplasm is a clear, jelly-like material.
- It fills space between nucleus and membrane.
- It is the cell's chemical factory.
- Organelles float inside it.
Organelles
The small structures inside the cytoplasm are called organelles. The biggest organelle is the nucleus. Others are mitochondria, golgi bodies and ribosomes. Plant cells also have chloroplasts.
Example 1 — Building New Substances
- Materials taken into the cell reach the cytoplasm.
- New substances are built there from these materials.
- So the cytoplasm acts like a busy factory.
Example 2 — Holding the Organelles
- The nucleus, mitochondria and ribosomes sit in the cytoplasm.
- Plant cells also have chloroplasts here.
- So the cytoplasm holds all the cell's machinery.
Important Points
- The cytoplasm holds mitochondria, ribosomes and golgi bodies.
- In plant cells it also holds the chloroplasts.
- The nucleus is the most prominent organelle within it.
Definition — Cytoplasm
The clear jelly-like material that fills the cell between the nucleus and the cell membrane and holds the organelles.
Nucleus
- The nucleus is a large, round organelle.
- It is the biggest organelle in all cells.
- A nuclear membrane wraps it.
- It controls all the cell's activities.
Chromosomes and Genes
The nucleus has thread-like structures called chromosomes. Chromosomes carry genes, which are the units of inheritance. They pass characters from parents to children. A tiny round structure inside, the nucleolus, is also present.
Example 1 — Nucleus in an Animal Cell
- In an animal cell the nucleus lies near the centre.
- It can be stained with a dye and seen easily.
- It directs everything the cell does.
Example 2 — Nucleus in a Plant Cell
- In a plant cell the nucleus is often near the edge.
- This is because a big vacuole takes the centre.
- It still controls the whole plant cell.
Important Points
- The nucleus is often called the "brain" of the cell.
- The nucleolus is a tiny round body inside the nucleus.
- Trap: mature red blood cells have no nucleus at all.
Definition — Nucleus
The large round organelle that controls all the activities of the cell and holds the chromosomes.
Mitochondria
- Mitochondria are tiny rod-shaped organelles.
- They are found in all cells.
- They give the cell its energy.
- Energy comes from respiration.
Example 1 — Burning Glucose
- Glucose is broken down using oxygen.
- This happens inside the mitochondria.
- So mitochondria use glucose and oxygen to make energy.
Example 2 — A Busy Muscle Cell
- A muscle cell needs a lot of energy to move.
- It has many mitochondria for this.
- So cells that work hard hold more mitochondria.
Important Points
- The energy is stored as a chemical called ATP.
- Busy cells like muscle cells hold the most mitochondria.
- Trap: mitochondria are in both plant and animal cells.
Definition — Mitochondria
Tiny organelles in all cells that release energy by breaking down glucose with oxygen.
Cell Wall
- Plant cells have a thick cell wall.
- It lies outside the cell membrane.
- It is made of tough cellulose.
- It gives shape and support.
Example 1 — A Standing Plant
- A plant is fixed at one place and cannot run away.
- The tough cell wall keeps its cells firm.
- So the cell wall helps the plant stay strong.
Example 2 — Onion Peel Cells
- Onion peel cells look like neat boxes.
- Their firm box shape comes from the cell wall.
- So the wall holds the plant cells together.
Important Points
- The wall is fully permeable — anything can pass through it.
- It lets a plant cell keep its firm, fixed shape.
- Trap: fungi and bacteria also have walls, but not of cellulose.
Definition — Cell Wall
The tough non-living covering of cellulose around a plant cell that gives it shape and support.
Plastids
- Plastids are coloured plant-cell organelles.
- Pigments are coloured matter.
- Plastids come in many colours.
- Green plastids are called chloroplasts.
Example 1 — Green Leaves
- Leaves are green because their cells have chloroplasts.
- Chloroplasts hold the green pigment chlorophyll.
- Food making by photosynthesis happens in chloroplasts.
Example 2 — Red Tomatoes
- A ripe tomato is red, not green.
- Its cells have plastids with red pigment.
- So different plastid colours give fruits and flowers their colours.
Important Points
- Roots are underground with no light, so they have no chloroplasts.
- The red of a tomato comes from a red-pigment plastid.
- Chlorophyll is the green pigment that traps sunlight.
Definition — Plastids
Coloured organelles in plant cells; the green ones with chlorophyll are chloroplasts, where food is made.
Vacuole
- A vacuole is a membrane-bound space.
- It holds substances dissolved in water.
- It looks empty under the microscope.
- Plant cells have a large vacuole.
Cell Sap
The liquid that fills the vacuole is called cell sap. It contains dissolved sugars and salts. Its pressure pushes on the cell and keeps the plant cell firm (turgid).
Example 1 — A Firm Plant Cell
- The big vacuole is full of cell sap.
- Its pressure pushes the cell outwards.
- So the plant cell stays firm and full.
Example 2 — Food Vacuole in Amoeba
- Amoeba is an animal cell with very small vacuoles.
- Its vacuoles hold food particles.
- So these are called food vacuoles.
Important Points
- The liquid inside the vacuole is called cell sap.
- A full vacuole keeps the plant cell firm, or turgid.
- Amoeba has a food vacuole that stores food particles.
Definition — Vacuole
A membrane-bound space in the cytoplasm that stores cell sap and other substances dissolved in water.
Comparison of Plant Cells and Animal Cells
Plant cells and animal cells are alike in many ways but differ in three big ways.
Main similarities
- Both have a cell membrane around them.
- Both have cytoplasm.
- Both have a nucleus and a nuclear membrane.
- Both have mitochondria.
| Plant Cell | Animal Cell |
|---|---|
| Has a cell wall around it. | Has no cell wall around it. |
| A photosynthetic plant cell has chloroplasts; other plant cells have different plastids. | Has no chloroplasts or other plastids. |
| Has a large vacuole in it. | Usually has no vacuole; only some animal cells have small vacuoles. |
Important Points
- Easy recall: plant-only parts are wall, chloroplast, big vacuole.
- An animal cell is usually rounder; a plant cell is more boxy.
- Trap: both cells share membrane, cytoplasm, nucleus and mitochondria.
Definition — Staining
Colouring the colourless parts of a cell with a dye so they can be seen clearly under the microscope.
Common Stains
Cell parts are colourless and hard to tell apart. So they are stained with dyes. Common dyes used for cells are dilute iodine solution, methylene blue solution and safranin.
Materials needed
An onion, forceps, a thin brush, petri dishes, safranin, water, glycerine, a glass slide, a cover slip, blotting paper and a microscope.
Procedure
Cut an onion into pieces and peel off the thin inner layer with forceps.
Place the peel in a petri dish and add a drop of safranin to stain it.
Transfer the peel to water to rinse off extra stain.
Place the peel on a glass slide and add a drop of glycerine so it does not dry.
Lower a cover slip slowly so no air bubble gets trapped.
Wipe off extra glycerine with blotting paper and view under a microscope.
Place the peel in a petri dish and add a drop of safranin to stain it.
Transfer the peel to water to rinse off extra stain.
Place the peel on a glass slide and add a drop of glycerine so it does not dry.
Lower a cover slip slowly so no air bubble gets trapped.
Wipe off extra glycerine with blotting paper and view under a microscope.
Observation
We see rectangular box-like cells arranged closely with no space between them. We can spot the cell membrane, cell wall, nucleus, cytoplasm and vacuole.
Explanation
Onion is a plant, so onion peel cells are plant cells. The neat box shape and the cell wall show that these are typical plant cells. This proves all plants are made of cells.
◆ Summary
- Onion peel is plant tissue
- Safranin stains the cells
- Glycerine stops drying
- Cells look like boxes
- Cell wall is visible
Objective Type Questions Q1(c) - Page 34 Lakhmir Singh
Question
Name the part of the cell which contains organelles.
Show answer
Cytoplasm.
Explanation
- Organelles float in the jelly-like cytoplasm.
- So the cytoplasm holds the cell's organelles.
Objective Type Questions Q1(d) - Page 34 Lakhmir Singh
Question
Name the kind of cells surrounded by a cell wall.
Show answer
Plant cells.
Explanation
- Only plant cells have an extra cell wall.
- It lies outside the cell membrane.
Objective Type Questions Q1(e) - Page 34 Lakhmir Singh
Question
Name the organelle of a plant cell where photosynthesis takes place.
Show answer
Chloroplast.
Explanation
- Chloroplast is a green plastid.
- It holds chlorophyll and makes food by photosynthesis.
Subjective Type Questions - Short Answer Q3 - Page 35 Lakhmir Singh
Question
What is a plastid? What is the name of green plastids present in plant cells?
Show answer
A plastid is a coloured organelle in plant cells. The green plastids are called chloroplasts.
Explanation
- Plastids contain pigments, which are coloured matter.
- Green plastids hold the pigment chlorophyll.
- These green plastids are called chloroplasts.
- Photosynthesis takes place in the chloroplasts.
Subjective Type Questions - Short Answer Q4 - Page 35 Lakhmir Singh
Question
What is the function of cell wall in a plant cell?
Show answer
The cell wall gives shape, support and strength to the plant cell and protects it.
Explanation
- The cell wall is made of a tough material called cellulose.
- It holds plant cells together and gives plants strength.
- It protects the plant from harsh conditions.
Subjective Type Questions - Short Answer Q5 - Page 35 Lakhmir Singh
Question
Name the parts of a cell which are found only in plants.
Show answer
Cell wall, chloroplasts (plastids) and a large vacuole.
Explanation
- The cell wall is a tough covering only plant cells have.
- Chloroplasts hold chlorophyll and make food in plant cells.
- A large vacuole storing cell sap is found in plant cells.
Subjective Type Questions - Short Answer Q6 - Page 35 Lakhmir Singh
Question
Various parts of a cell are given below. Write them in the appropriate places in the following diagram: Nucleus, Cytoplasm, Chloroplast, Cell wall, Cell membrane, Nucleoid. (NCERT Book Question)
Show answer
Common to all three: cell membrane, cytoplasm, nucleus. Only in plant cell: cell wall, chloroplast. Only in bacterial cell: nucleoid.
Explanation
- Cell membrane, cytoplasm and nucleus are in all three cells.
- Cell wall and chloroplast are placed only in the plant cell.
- Bacteria have a nucleoid instead of a true nucleus.
- The animal cell here has only the three common parts.
Subjective Type Questions - Long Answer Q1(a) - Page 35 Lakhmir Singh
Question
What is cytoplasm? What is its function?
Show answer
Cytoplasm is the jelly-like material between the nucleus and the membrane; it is where most chemical reactions of the cell happen.
Explanation
- Cytoplasm holds the organelles of the cell.
- It acts like a chemical factory where substances are built.
- Most life processes take place within it.
Subjective Type Questions - Long Answer Q2 - Page 35 Lakhmir Singh
Question
Draw the general diagram of an animal cell and label it.
Show answer
An animal cell diagram should show and label the cell membrane, cytoplasm, nucleus, nucleolus, nuclear membrane and mitochondria.
Explanation
- Draw a rounded shape for the animal cell.
- Mark the thin outer cell membrane.
- Show the nucleus near the centre with its nucleolus.
- Add a few rod-shaped mitochondria; no cell wall or chloroplasts.
Subjective Type Questions - Long Answer Q3(a) - Page 35 Lakhmir Singh
Question
State three differences between a plant cell and an animal cell.
Show answer
A plant cell has a cell wall, chloroplasts and a large vacuole; an animal cell has none of these.
Explanation
- Difference 1: A plant cell has a cell wall; an animal cell does not.
- Difference 2: A plant cell has chloroplasts; an animal cell does not.
- Difference 3: A plant cell has a large vacuole; an animal cell has small or none.
Multiple Choice Questions Q1 - Page 36 Lakhmir Singh
Question
The organelles which provide energy for all the activities of a cell are: (a) chloroplasts (b) mitochondria (c) golgi bodies (d) ribosomes
Show answer
(b) mitochondria.
Explanation
- Mitochondria are the power-houses of the cell.
- They release energy by respiration.
Multiple Choice Questions Q2 - Page 36 Lakhmir Singh
Question
The cell wall in onion peel cell is made of: (a) starch (b) gelatin (c) cellulose (d) cell sap
Show answer
(c) cellulose.
Explanation
- The plant cell wall is made of tough cellulose.
Multiple Choice Questions Q6 - Page 36 Lakhmir Singh
Question
Which of the following organelle is not found in the root cells of a plant? (a) nucleus (b) vacuole (c) mitochondria (d) chloroplasts
Show answer
(d) chloroplasts.
Explanation
- Roots are underground with no sunlight.
- So root cells have no chloroplasts for photosynthesis.
Multiple Choice Questions Q7 - Page 36 Lakhmir Singh
Question
The part of a cell which is found only in a plant cell: (a) nucleus (b) ribosome (c) cell wall (d) cell membrane
Show answer
(c) cell wall.
Explanation
- The cell wall is found only in plant cells.
- Animal cells have no cell wall.
Multiple Choice Questions Q10 - Page 37 Lakhmir Singh
Question
A photosynthetic plant cell: (a) xylem (b) phloem (c) epidermal cell (d) mesophyll cell
Show answer
(d) mesophyll cell.
Explanation
- Mesophyll cells of a leaf have chloroplasts.
- So they carry out photosynthesis.
21st Century Skills Q1 - Page 37 Lakhmir Singh
Question
The parts P and Q are present only in plant cells. Part P contains a green pigment called R, whereas part Q is made of a tough material S. Part P takes part in food making, whereas part Q gives shape and support. (a) What is (i) P, and (ii) Q? (b) What is (i) R, and (ii) S?
Show answer
(a) (i) P is chloroplast, (ii) Q is cell wall. (b) (i) R is chlorophyll, (ii) S is cellulose.
Explanation
- P makes food and holds green pigment, so P is the chloroplast.
- The green pigment R inside it is chlorophyll.
- Q gives shape and support, so Q is the cell wall.
- The tough material S of the wall is cellulose.
21st Century Skills Q2 - Page 37 Lakhmir Singh
Question
The cytoplasm of the cells of a tomato plant contains organelle X having different pigments which give different colours to the leaves and fruits. (a) What is the general name of organelles X? (b) What is the (i) name, (ii) colour, and (iii) function of X in the leaves? (c) What is the colour of X in the ripe fruits?
Show answer
(a) The organelles X are plastids. (b) In the leaves: (i) chloroplast, (ii) green, (iii) makes food by photosynthesis. (c) In ripe fruits the plastid is red.
Explanation
- Plastids are coloured organelles in plant cells.
- In leaves the plastid is the green chloroplast.
- The chloroplast makes food by photosynthesis.
- In ripe tomatoes the plastid carries red pigment.
