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Cell Organelles and Functions ICSE Class 9 Biology

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BiologyICSE Class 9 · Cell: The Unit of Life

Cell Organelles and Their Functions (ICSE Class 9 Biology)

Updated 17 October 2026 · Fact-checked

Organelles are the small structures inside the cytoplasm that each do a particular job. The nucleus controls the cell, the endoplasmic reticulum carries materials and makes proteins and lipids, ribosomes build proteins, the Golgi apparatus packs and dispatches them, mitochondria release energy, plastids store pigments or food, lysosomes digest waste and vacuoles store water and wastes.

Understand Cell Organelles and Their Functions

1. Nucleus. Surrounded by a double nuclear membrane with pores, it holds chromatin (DNA with protein), which condenses into chromosomes at division, and one or more dense nucleoli that make ribosomal material. It controls all cell activities and carries heredity.

2. Endoplasmic reticulum (ER). A network of membrane-bound channels joined to the nuclear membrane. *Rough ER* has ribosomes on its surface and helps in protein synthesis and transport; *smooth ER* has none and makes lipids and steroids and helps detoxification. Together they form the cell's transport network.

3. Ribosomes. Tiny granules, free in the cytoplasm or attached to rough ER, where amino acids are joined into proteins. They have no membrane and are called the protein factories.

4. Golgi apparatus. A stack of flattened sacs with vesicles at the edges. It receives proteins and lipids from the ER, modifies and packs them into vesicles and dispatches them; in plant cells it helps make the cell wall.

5. Mitochondria. Rod-shaped, double-membrane organelles; the inner membrane is folded into cristae. They release energy from food by aerobic respiration and store it as ATP, so they are the powerhouses and are numerous in active cells such as muscle cells. They contain their own DNA and ribosomes.

6. Plastids (plant cells). *Chloroplasts* are green because of chlorophyll and carry out photosynthesis; *chromoplasts* hold yellow, orange or red pigments (as in petals and ripe fruits); *leucoplasts* are colourless and store starch, oil or protein.

7. Lysosomes. Single-membrane sacs of digestive enzymes that digest worn-out organelles, food and germs; if the cell is damaged they may burst and digest it, hence suicide bags.

8. Vacuoles and centrosome. Vacuoles are fluid-filled sacs: one large central vacuole in a mature plant cell keeps it firm and stores sap, while animal cells have small vacuoles. The centrosome, with two centrioles, is found in animal cells near the nucleus and organises the spindle at cell division.

Cell Organelles and Their Functions: key facts

Nucleus
  • Double membrane
  • Chromatin
  • Nucleolus
  • Controls cell activities
  • Carries heredity
Powerhouse and protein factory
  • Mitochondria release energy as ATP
  • Ribosomes make proteins
  • Rough ER carries ribosomes
Plastids
  • Chloroplast green: photosynthesis
  • Chromoplast coloured
  • Leucoplast colourless: storage
Digest and pack
Lysosome: digestive enzymes, suicide bag | Golgi: modifies, packs, dispatches

Cell Organelles and Their Functions in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

A city factory

Suppose a cell is a small factory town: an office gives orders, workers build items, a packing department boxes them, a power station supplies energy and a waste unit breaks down scrap.

Match the town departments to organelles.

Try it first, then show the solutionSolution
  1. Office giving orders: nucleus.
  2. Workers building items: ribosomes.
  3. Packing and dispatch: Golgi apparatus.
  4. Power station: mitochondria.
  5. Waste unit: lysosomes.

Answer: Nucleus, ribosomes, Golgi, mitochondria, lysosomes in that order.

Memory hook: Order, build, pack, power, clean.

Tricks to remember Cell Organelles and Their Functions

Short memory aids. Say each one aloud once, then use it on a question the same day.

  • Mito = money

    Mitochondria make the energy currency (ATP).

    Use it when: Powerhouse questions.

  • R-R-R

    Rough ER has Ribosomes and helps in protein transport; smooth ER has none and helps lipids.

    Use it when: Rough versus smooth ER.

  • Leuco = white

    Leucoplast is colourless, chromo is colour, chloro is green.

    Use it when: Plastid types.

Cell Organelles and Their Functions: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Name the organelle · 3 marks · Short answerBoard level

Name the organelle that (a) is called the suicide bag, (b) has cristae, (c) packs and dispatches proteins. [3]

Try it first, then show the solutionSolution
  1. (a) Lysosome.
  2. (b) Mitochondria: the inner membrane is folded into cristae.
  3. (c) Golgi apparatus.

Answer: (a) Lysosome (b) Mitochondria (c) Golgi apparatus.

Example 2: ER and cell type · 3 marks · Short answerHarder board level

A gland cell makes large amounts of an enzyme, while another cell makes steroid hormones. Which type of ER would you expect to be more abundant in each, and why? [3]

Try it first, then show the solutionSolution
  1. Enzymes are proteins, and proteins are made on ribosomes attached to rough ER, so the enzyme cell has abundant rough ER.
  2. Steroids are lipids, made by smooth ER, so the steroid-secreting cell has abundant smooth ER.
  3. Both ER types are joined, so materials pass between them.

Answer: Enzyme cell: rough ER, which carries ribosomes; steroid cell: smooth ER, which makes lipids and steroids.

Example 3: Why mitochondria are numerous · 3 marks · Short answerHarder board level

A muscle cell has far more mitochondria than a skin cell. Explain this difference, linking structure to function. [3]

Try it first, then show the solutionSolution
  1. Mitochondria release energy in the form of ATP by aerobic respiration.
  2. Muscle cells contract repeatedly and need a large supply of energy.
  3. The folded cristae give a large surface for the reactions, and more mitochondria give more ATP.

Answer: Muscle cells need more energy, so they carry more mitochondria.

Example 4: Linking the organelles · 4 marks · Long answerHarder board level

Trace the path of a protein from its making to its release from the cell, naming the organelles in order. [4]

Try it first, then show the solutionSolution
  1. Ribosomes on the rough ER join amino acids into the protein.
  2. The protein passes through the channels of the ER.
  3. Vesicles carry it to the Golgi apparatus, which modifies and packs it.
  4. Vesicles from the Golgi move to the cell membrane and release it.

Answer: Ribosome on rough ER, ER channels, Golgi apparatus, vesicle, cell membrane.

Example 5: Case: a damaged cell · 6 marks · Case-basedHOTS / competency

Case. A cell is damaged by a poison and its lysosomes burst. (i) What will be released? [1] (ii) What will happen to the cell? [1] (iii) Why does the cell normally stay safe? [2] (iv) Why would a plant cell with a large vacuole be affected less by a small leak of enzymes? [2]

Try it first, then show the solutionSolution
  1. (i) Digestive enzymes.
  2. (ii) The cell digests itself and dies.
  3. (iii) The enzymes are enclosed by the lysosome membrane.
  4. (iv) A large vacuole dilutes and holds materials away from the cytoplasm.

Answer: (i) Digestive enzymes (ii) The cell is digested (autolysis) (iii) The membrane keeps the enzymes enclosed (iv) The central vacuole dilutes and holds the contents away.

Where students lose marks in Cell Organelles and Their Functions

The slips examiners see most often, and what to write instead.

  • Mistake: Calling mitochondria the producers of energy

    Energy is released from food, not created.

    Do this: Write that mitochondria release energy and store it as ATP.

    Usually costs: 1 mark.

  • Mistake: Mixing up chloroplasts and chromoplasts

    Both are coloured plastids.

    Do this: Chloroplasts are green and photosynthesise; chromoplasts hold other pigments.

    Usually costs: 1 mark.

  • Mistake: Saying ribosomes are made of a membrane

    Ribosomes have no membrane.

    Do this: Say granules made of RNA and protein, without a membrane.

    Usually costs: 1 mark.

Exam tips

  • Always link each organelle to one function in a single phrase.
  • Rough versus smooth ER answers need the ribosome point first.
  • Write what each organelle contains: cristae, chromatin, enzymes.
  • Draw labelled diagrams neatly with lines and no arrowheads.

Practice questions on Cell Organelles and Their Functions

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

  1. Q1 · 1 mark · MCQBoard level

    Which organelle contains cristae?
    (a) Golgi apparatus
    (b) Mitochondria
    (c) Lysosome
    (d) Ribosome

    Hint

    Powerhouse.

    Answer

    (b) Mitochondria.

  2. Q2 · 2 marks · Very short answerBoard level

    Which plastid would you find in a potato tuber, and which in a red chilli? State the function of each. [2]

    Hint

    Leuco- and chromo-.

    Answer

    Leucoplast in the tuber stores starch; chromoplast in the chilli holds the red pigment.

  3. Q3 · 2 marks · Short answerBoard level

    What is the function of the nucleolus, and why is it important? [2]

    Hint

    Ribosomes.

    Answer

    The nucleolus makes the material for ribosomes, so it is needed for protein synthesis.

  4. Q4 · 1 mark · Assertion-reasonHarder board level

    Assertion (A): Ribosomes are called protein factories.
    Reason (R): Amino acids are joined into proteins on ribosomes.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

    Hint

    Where are proteins made?

    Answer

    (a).

  5. Q5 · 3 marks · Short answerBoard level

    Explain how lysosomes can both protect a cell and, when damaged, kill it. [3]

    Hint

    Digest.

    Answer

    They contain digestive enzymes that digest worn-out organelles, food and germs, which protects the cell; if they burst, the enzymes digest the whole cell.

  6. Q6 · 3 marks · Short answerHarder board level

    Mitochondria and chloroplasts both have their own DNA and ribosomes and both make energy-rich molecules. State two differences between them in function and location. [3]

    Hint

    Which uses light?

    Answer

    Chloroplasts are in plant cells and capture light energy to make food in photosynthesis; mitochondria are in plant and animal cells and release energy from food in respiration.

  7. Q7 · 2 marks · Very short answerHarder board level

    Name the organelle with two centrioles that organises the spindle during division of an animal cell, and state where it lies. [2]

    Hint

    Spindle.

    Answer

    The centrosome; it lies near the nucleus.

  8. Q8 · 3 marks · Short answerHarder board level

    Plant cells kept in strong salt solution shrink. Which organelle shrinks most and why does this loosen the cell contents? [3]

    Hint

    Water store.

    Answer

    The large central vacuole loses water to the salt solution, so the cell contents shrink away from the cell wall.

  9. Q9 · 3 marks · Long answerHOTS / competency

    A student says the Golgi apparatus makes proteins. Correct her statement and explain what it actually does with proteins. [3]

    Hint

    Ribosome versus Golgi.

    Answer

    Proteins are made by ribosomes. The Golgi apparatus receives them from the ER, modifies them, packs them into vesicles and dispatches them.

  10. Q10 · 4 marks · Case-basedHOTS / competency

    Case. A drug stops the folding of the inner membrane of mitochondria. (i) Name the folds. [1] (ii) Predict the effect on energy release. [2] (iii) Which cells would be most affected? Give a reason. [1]

    Hint

    Surface area.

    Answer

    (i) Cristae. (ii) Less surface for the respiration reactions, so less ATP is made. (iii) Muscle cells, because they need a large amount of energy.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

  1. 1.Powerhouse of the cell?Show answer

    Mitochondria.

  2. 2.Organelle for packing and dispatch?Show answer

    Golgi apparatus.

  3. 3.Where are proteins made?Show answer

    On ribosomes.

  4. 4.Colourless plastid?Show answer

    Leucoplast.

  5. 5.Why are lysosomes called suicide bags?Show answer

    Their enzymes can digest the whole cell.

Cell Organelles and Their Functions: frequently asked questions

Do plant cells have lysosomes?

They are mainly described in animal cells; plant vacuoles do some digestive work.

Is the nucleolus an organelle?

It is a dense body inside the nucleus, not enclosed by its own membrane.

Which organelles have double membranes?

The nucleus, mitochondria and chloroplasts.