What are the main components of a cell according to the Cambridge IGCSE Coordinated Science syllabus?

The main components of a cell include the cell membrane, cytoplasm, nucleus, mitochondria, and ribosomes. In plant cells, additional structures such as the cell wall, chloroplasts, and a large central vacuole are also present. These components work together to maintain cell function and structure.

How does the cell membrane function in cell structure?

The cell membrane, also known as the plasma membrane, is a crucial component of cell structure. It acts as a selective barrier, controlling the movement of substances in and out of the cell. This semi-permeable membrane is composed of a phospholipid bilayer with embedded proteins, which help in communication and transport processes.

What is the role of the nucleus in a cell?

The nucleus is often referred to as the control center of the cell. It contains the cell's genetic material (DNA) and is responsible for regulating gene expression and cell division. The nucleus is surrounded by a nuclear envelope, which protects the DNA and controls the passage of molecules in and out of the nucleus.

Why are mitochondria known as the powerhouse of the cell?

Mitochondria are known as the powerhouse of the cell because they are the primary site of ATP (adenosine triphosphate) production through the process of cellular respiration. ATP is the energy currency of the cell, providing the necessary energy for various cellular activities.

What distinguishes plant cells from animal cells in terms of cell structure?

Plant cells differ from animal cells in several ways. Plant cells have a rigid cell wall made of cellulose, chloroplasts for photosynthesis, and a large central vacuole for storage and maintaining cell turgor. In contrast, animal cells lack these structures but have centrioles involved in cell division.

Why is "Confusing the cell wall with the cell membrane" a common mistake in Cell Structure ?

Why it happens: Both are boundaries of the cell. Students use the terms interchangeably. How to avoid it: Cell wall = rigid, cellulose, outside, plant only, support. Cell membrane = thin, flexible, controls entry/exit of substances, present in all cells.

Why is "Including units in the magnification answer (e.g. writing '×600 mm')" a common mistake in Cell Structure ?

Why it happens: Students forget that magnification is a ratio and therefore has no units. How to avoid it: Magnification = image ÷ actual; units cancel. Write simply '×600' or '600'.

Why is "Stating that all plant cells contain chloroplasts" a common mistake in Cell Structure ?

Why it happens: Photosynthesis is associated with plants, so students assume every plant cell carries out photosynthesis. How to avoid it: Chloroplasts are only in cells exposed to light (e.g. palisade cells, guard cells). Root cells have no chloroplasts.

Why is "Stating that red blood cells have a nucleus" a common mistake in Cell Structure ?

Why it happens: Most cells have a nucleus, and students apply this as a general rule. How to avoid it: Mature red blood cells in mammals have no nucleus (or mitochondria) — the nucleus is expelled during development to maximise space for haemoglobin.

CellsCambridge IGCSE Coordinated Sciences 0654

Cell Structure

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Cell Structure — Cambridge IGCSE Coordinated Science 0654

Cells are the basic units of life. Animal and plant cells share some organelles but plant cells have additional structures. Prokaryotic cells (bacteria) lack a membrane-bound nucleus. Every organelle has a specific function — these are tested in every Paper 4.

What you’ll learn

Mapped to the Cambridge IGCSE 0654 syllabus (2025-2027).

B2.1 — Describe the structure of typical animal and plant cells.
B2.1 — State the functions of cell membrane, cell wall, nucleus, cytoplasm, mitochondria, ribosomes, chloroplasts, vacuole.
B2.2 — Compare prokaryotic and eukaryotic cells.
B2.3 — Describe examples of cell specialisation and explain how structure relates to function.

Animal vs Plant Cell — Organelle by Organelle

Know every organelle's function. Exam questions ask for function, not just name.

Organelles found in BOTH animal and plant cells:

Organelle	Function
Cell membrane	Selectively permeable barrier — controls what enters and leaves the cell
Nucleus	Contains DNA (chromosomes); controls all cell activities and protein synthesis
Cytoplasm	Jelly-like fluid; site of many chemical reactions including anaerobic respiration
Mitochondria	Site of aerobic respiration — releases energy (ATP) from glucose
Ribosomes	Site of protein synthesis — translates mRNA into proteins

Organelles found ONLY in plant cells:

Organelle	Function
Cell wall (cellulose)	Provides structural support; fully permeable; prevents the cell bursting
Chloroplasts	Contain chlorophyll; site of photosynthesis; only in green parts
Permanent vacuole	Contains cell sap; maintains turgor pressure; keeps plant rigid

Key comparisons examiners test:

Feature	Animal	Plant
Cell wall	✗	✓ (cellulose)
Chloroplasts	✗	✓ (green parts only)
Large permanent vacuole	✗	✓
Shape	Irregular	Regular, fixed

Both cells share a membrane, nucleus, cytoplasm, mitochondria and ribosomes; plant cells add a cellulose cell wall, chloroplasts and a large permanent vacuole.

Cell membrane (selectively permeable) ≠ cell wall (fully permeable, structural).
Mitochondria: more active cell = more mitochondria (e.g. muscle, liver cells).
Ribosomes are the smallest organelle — found in ALL living cells.
Not all plant cells have chloroplasts — root cells, for example, are white.

Prokaryotic vs Eukaryotic Cells

Prokaryotes (bacteria) have NO nucleus. All other organisms are eukaryotes.

Eukaryotic cells (animals, plants, fungi): have a membrane-bound nucleus containing linear chromosomes.

Prokaryotic cells (bacteria): have NO membrane-bound nucleus.

Feature	Prokaryotic	Eukaryotic
Nucleus	✗ (DNA is free, circular, in cytoplasm)	✓ (membrane-bound, linear DNA)
Mitochondria	✗	✓
Chloroplasts	✗	✓ (in plants only)
Cell wall	✓ (NOT cellulose)	✓ (plants — cellulose; fungi — chitin)
Size	Smaller (~1–10 µm)	Larger (~10–100 µm)
Ribosomes	✓ (smaller: 70S)	✓ (larger: 80S)

Why this matters for antibiotics: Antibiotics target structures unique to prokaryotes (e.g. the bacterial cell wall composition). This is why antibiotics can kill bacteria without harming your own (eukaryotic) cells.

Prokaryotes: no membrane-bound nucleus; circular DNA free in cytoplasm.
Both have ribosomes and cell membranes — ribosomes are universal.
Prokaryotic cell walls are NOT made of cellulose.

Cell Specialisation — Structure Matches Function

Specialised cells have modified structures that make them exceptionally good at one job.

All cells in a multicellular organism contain the same DNA. Specialised cells differ because they express different genes.

Cell Type	Special Feature(s)	Function
Red blood cell	Biconcave disc; no nucleus; full of haemoglobin	Maximise O₂ carried; fit through narrow capillaries
Root hair cell	Long hair-like extension; large vacuole	Maximise surface area for water and mineral absorption
Palisade mesophyll	Packed with chloroplasts; tall, cylindrical	Maximum photosynthesis
Sperm cell	Long flagellum (tail); many mitochondria; acrosome	Swim to egg; enzyme to penetrate egg
Ciliated epithelial	Cilia on surface	Sweep mucus (with trapped pathogens) up the airways
Guard cell	Contains chloroplasts; changes shape	Controls opening and closing of stomata
Nerve cell (neurone)	Very long axon; myelin sheath	Rapid transmission of electrical impulses

Structure → function logic (exam technique): When asked to explain an adaptation, always link the structural feature to the specific function. E.g. "The red blood cell has no nucleus, leaving MORE SPACE for haemoglobin, so it can carry MORE oxygen per cell."

Biconcave disc + no nucleus → maximum O₂ carrying capacity in red blood cells.
Long extension on root hair cells → maximum surface area for absorption.
Palisade cells packed with chloroplasts → maximum photosynthesis per unit volume.
Sperm: many mitochondria → ATP for swimming; acrosome → enzyme to penetrate egg.

How it’s examined

Paper 2 multiple choice: identify organelles from descriptions or diagrams. Paper 4: 'State TWO differences between a plant cell and an animal cell' (2 marks); 'Explain how the structure of the red blood cell is adapted for its function' (4 marks). Prokaryote vs eukaryote comparison is a favourite 4-mark question. Always give function alongside structure — naming alone scores 0 for 'explain' questions.

Sources: Cambridge IGCSE Coordinated Sciences 0654 syllabus 2025-2027 (B2); 0654/42 May/Jun 2023 — Q2 (cell structure); 0654 Examiner Reports 2022-2024. Last reviewed 2026-05-14.

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Step-by-step worked examples — Cell Structure

Step-by-step solutions to past-paper-style questions on cell structure , written exactly the way a tutor would explain them at the board.

1Calculate magnification from image and actual size
Extended• magnification, calculation
Question
A student views a cell under a microscope. The image of the cell is 30 mm wide. The actual cell is 0.05 mm wide. Calculate the magnification.
Step-by-step solution
1. Step 1
  Write the magnification formula.
  $\text{magnification} = \dfrac{\text{image size}}{\text{actual size}}$
2. Step 2
  Substitute the values. Both measurements must be in the same unit (mm).
  $\text{magnification} = \dfrac{30}{0.05} = 600$
3. Step 3
  State the answer. Magnification has no units.
Answer
Magnification = ×600
Examiner tip
Always check that image size and actual size are in the same unit before dividing. A common error is mixing mm and µm.
2State TWO differences between a plant cell and an animal cell
Core• plant cell, animal cell
Question
State TWO differences between a plant cell and an animal cell.
Step-by-step solution
1. Step 1
  Identify structures present in plant cells but absent in animal cells.
2. Step 2
  Plant cells have a cellulose cell wall; animal cells do not. Plant cells have chloroplasts (in photosynthetic cells); animal cells do not. Plant cells have a large permanent vacuole; animal cells have no permanent vacuole (or only small, temporary ones).
Answer
Any TWO from: plant cells have a cell wall / chloroplasts / a permanent vacuole; animal cells do not.
3Why red blood cells do not carry out aerobic respiration
Extended• red blood cell, mitochondria, adaptation
Question
Explain why red blood cells do not carry out aerobic respiration despite transporting oxygen.
Step-by-step solution
1. Step 1
  Red blood cells are unusual because they have no mitochondria (and no nucleus — they were expelled during development).
2. Step 2
  Aerobic respiration occurs in the mitochondria. Without mitochondria, the cell cannot use the oxygen it is carrying for aerobic respiration.
3. Step 3
  Red blood cells instead rely on anaerobic respiration (glycolysis) for their energy needs, ensuring all the oxygen they carry is available for delivery to body tissues.
Answer
Red blood cells have no mitochondria; aerobic respiration occurs in mitochondria, so without them the cell cannot carry out aerobic respiration. All oxygen carried is thus available for delivery to body cells.
4State the function of the mitochondria
Core• mitochondria, organelle function
Question
State the function of the mitochondria.
Step-by-step solution
1. Step 1
  Mitochondria are the site of aerobic respiration — the process that releases energy (ATP) from glucose using oxygen.
Answer
The mitochondria are the site of aerobic respiration, where energy (ATP) is released from glucose.
Examiner tip
Do not write 'produces energy' — the correct phrasing is 'releases energy' or 'site of aerobic respiration'.
5Adaptation of a root hair cell
Extended• root hair cell, adaptation, surface area
Question
Explain one adaptation of a root hair cell for its function of absorbing water and mineral ions from the soil.
Step-by-step solution
1. Step 1
  Root hair cells have a long, thin hair-like extension that projects into the soil. This greatly increases the surface area of the cell membrane in contact with soil water.
2. Step 2
  A larger surface area allows faster rates of osmosis (for water uptake) and active transport (for mineral ion uptake) per unit time.
Answer
Root hair cells have a long, hair-like extension that increases surface area; this allows faster absorption of water by osmosis and mineral ions by active transport from the soil.

Key Formulae — Cell Structure

The formulae you need to memorise for cell structure on the Cambridge IGCSE 0654 paper, with every variable defined in plain English and a note on when to use it.

Magnification
$\text{magnification} = \dfrac{\text{image size}}{\text{actual size}}$
$\text{image size}$
the size of the image seen through the microscope (e.g. in mm)
$\text{actual size}$
the real size of the object (same unit as image size)
When to use
Any question that gives two of the three values (magnification, image size, actual size) and asks for the third.
Example
Image = 30 mm, actual = 0.05 mm → magnification = 30 ÷ 0.05 = ×600

Key Definitions and Keywords — Cell Structure

Definitions to memorise and the exact keywords mark schemes credit for cell structure answers — sharpened from recent examiner reports for the 2026 0654 sitting.

Cell membrane
Examiner keyword
A thin, partially permeable membrane surrounding the cell that controls which substances enter and leave the cell.
Nucleus
Examiner keyword
An organelle enclosed by a nuclear membrane that contains the cell's DNA; it controls the activities of the cell and carries genetic information.
Mitochondria
Examiner keyword
Organelles that are the site of aerobic respiration; they release energy (as ATP) from glucose.
Ribosome
Examiner keyword
Tiny organelles found in the cytoplasm (and on rough ER) where proteins are synthesised.
Cell wall
Examiner keyword
A rigid outer layer made of cellulose surrounding plant cells; it provides structural support and prevents the cell from bursting.
Chloroplast
Examiner keyword
An organelle found in green plant cells that contains chlorophyll and is the site of photosynthesis.
Magnification
Examiner keyword
The number of times larger an image is compared with the actual size of the object. Magnification = image size ÷ actual size.

Common Mistakes and Misconceptions — Cell Structure

The traps other students keep falling into on cell structure questions — taken from recent Cambridge IGCSE 0654 examiner reports and mark schemes — and how to avoid them.

✕Confusing the cell wall with the cell membrane
Why it happens
Both are boundaries of the cell. Students use the terms interchangeably.
How to avoid it
Cell wall = rigid, cellulose, outside, plant only, support. Cell membrane = thin, flexible, controls entry/exit of substances, present in all cells.
✕Including units in the magnification answer (e.g. writing '×600 mm')
Why it happens
Students forget that magnification is a ratio and therefore has no units.
How to avoid it
Magnification = image ÷ actual; units cancel. Write simply '×600' or '600'.
✕Stating that all plant cells contain chloroplasts
Why it happens
Photosynthesis is associated with plants, so students assume every plant cell carries out photosynthesis.
How to avoid it
Chloroplasts are only in cells exposed to light (e.g. palisade cells, guard cells). Root cells have no chloroplasts.
✕Stating that red blood cells have a nucleus
Why it happens
Most cells have a nucleus, and students apply this as a general rule.
How to avoid it
Mature red blood cells in mammals have no nucleus (or mitochondria) — the nucleus is expelled during development to maximise space for haemoglobin.

Practice questions

Exam-style questions with step-by-step worked solutions. Try one before checking the method.

Past paper style quiz

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Cell Structure — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Cell Structure

Short Study Notes in the form of Slides

Short Study Notes — Cell Structure

Detailed Notes

What you’ll learn

How it’s examined

1Calculate magnification from image and actual size

2State TWO differences between a plant cell and an animal cell

3Why red blood cells do not carry out aerobic respiration

4State the function of the mitochondria

5Adaptation of a root hair cell

Magnification

Cell membrane

Nucleus

Mitochondria

Ribosome

Cell wall

Chloroplast

Magnification

✕Confusing the cell wall with the cell membrane

✕Including units in the magnification answer (e.g. writing '×600 mm')

✕Stating that all plant cells contain chloroplasts

✕Stating that red blood cells have a nucleus

Practice questions

Past paper style quiz

Assess your understanding

Cell Structure — frequently asked questions