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Detailed notes on Cells for Cambridge IGCSE Coordinated Science, covering key concepts, explanations, examples, and exam-focused revision points.
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.
Mapped to the Cambridge IGCSE 0654 syllabus (2025-2027).
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 |
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.
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."
Verbatim phrases and definitions Cambridge mark schemes credit.
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.
Step-by-step solutions to past-paper-style questions on cell structure , written exactly the way a tutor would explain them at the board.
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
Step 1
Write the magnification formula.
magnification=actual sizeimage size
Step 2
Substitute the values. Both measurements must be in the same unit (mm).
magnification=0.0530=600
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.
Question
State TWO differences between a plant cell and an animal cell.
Step-by-step solution
Step 1
Identify structures present in plant cells but absent in animal cells.
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.
Question
Explain why red blood cells do not carry out aerobic respiration despite transporting oxygen.
Step-by-step solution
Step 1
Red blood cells are unusual because they have no mitochondria (and no nucleus — they were expelled during development).
Step 2
Aerobic respiration occurs in the mitochondria. Without mitochondria, the cell cannot use the oxygen it is carrying for aerobic respiration.
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.
Question
State the function of the mitochondria.
Step-by-step solution
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'.
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
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.
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.
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=actual sizeimage 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
Definitions to memorise and the exact keywords mark schemes credit for cell structure answers — sharpened from recent examiner reports for the 2026 0654 sitting.
A thin, partially permeable membrane surrounding the cell that controls which substances enter and leave the cell.
An organelle enclosed by a nuclear membrane that contains the cell's DNA; it controls the activities of the cell and carries genetic information.
Organelles that are the site of aerobic respiration; they release energy (as ATP) from glucose.
Tiny organelles found in the cytoplasm (and on rough ER) where proteins are synthesised.
A rigid outer layer made of cellulose surrounding plant cells; it provides structural support and prevents the cell from bursting.
An organelle found in green plant cells that contains chlorophyll and is the site of photosynthesis.
The number of times larger an image is compared with the actual size of the object. Magnification = image size ÷ actual size.
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.
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 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 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 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.
The things students keep getting wrong in this sub-topic, answered.