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Detailed notes on Organisation of the Organism for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
What's inside a cell, what each part does, and how cells specialise. Plus the difference between animal and plant cells. Cambridge wants the FUNCTION named, not just the organelle.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Plant cells have cell wall + chloroplasts + permanent vacuole. Animal cells don't.
Both animal and plant cells have:
Plant cells ALSO have (animal cells don't):
| Structure | Animal cell | Plant cell | Function |
|---|---|---|---|
| Cell membrane | ✓ | ✓ | Selectively permeable; controls what enters and leaves |
| Cytoplasm | ✓ | ✓ | Jelly-like material where most reactions happen |
| Nucleus | ✓ | ✓ | Contains DNA; controls cell activity |
| Mitochondria | ✓ | ✓ | Site of aerobic respiration |
| Ribosomes | ✓ | ✓ | Site of protein synthesis |
| Cellulose cell wall | ✗ | ✓ | Rigid outer layer; gives shape and support |
| Chloroplasts | ✗ | ✓ | Site of photosynthesis |
| Large permanent vacuole | ✗ | ✓ | Holds cell sap; provides turgor |
Drawing tips for Cambridge.
Worked qualitative. Why are plant cells more rigid than animal cells?
Cambridge tip. When labelling diagrams, label BOTH the cell wall AND the cell membrane in plant cells — they're different structures. Many students label only one.
Memorise the FUNCTION, not just the name. Cambridge mark schemes need the function.
Nucleus.
Cell membrane.
Cytoplasm.
Mitochondrion.
Ribosome.
Chloroplast (plant only).
Cell wall (plant only).
Permanent vacuole (plant only).
Cell → tissue → organ → organ system → organism. Each level builds on the one below.
Five levels (smallest to largest).
1. Cell. Single unit. Carries out all life processes (in a single cell organism) or a specialised role (in a multicellular organism).
2. Tissue. A group of SIMILAR cells working together for a shared function.
3. Organ. A structure made of DIFFERENT tissues working together.
4. Organ system. A group of organs working together for a major function.
5. Organism. A whole living thing — combination of organ systems working together.
Worked qualitative. "Is the eye a cell, tissue, organ, or organ system?" The eye contains DIFFERENT tissues (lens, retina, cornea, muscles, blood vessels) working together — so it's an ORGAN.
Worked qualitative. Place the following in order: muscle cell, leg, leg muscle (biceps), human, muscular system. Cell → tissue (muscle tissue / biceps belly) → organ (a single muscle like biceps) → organ system (muscular system) → organism (human).
Verbatim phrases and definitions Cambridge mark schemes credit.
Cell structure appears every Paper 2 (3-5 marks: label diagram, state functions) and Paper 4 (5-7 marks: distinguish animal/plant, link to specialised cells). Examiner reports flag students stating only the name of an organelle without its function, and confusing cell wall with cell membrane.
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (2.1); 0610/22 May/Jun 2024 — Q4 (cell structure); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on cell structure and organisation, written exactly the way a tutor would explain them at the board.
Question
State the function of: (a) nucleus, (b) mitochondrion, (c) ribosome, (d) cell membrane.
Step-by-step solution
Step 1
(a) Nucleus: contains the DNA / genetic material; controls the activity of the cell.
Step 2
(b) Mitochondrion: site of (aerobic) respiration; releases energy from glucose.
Step 3
(c) Ribosome: site of protein synthesis.
Step 4
(d) Cell membrane: controls what enters and leaves the cell (selectively permeable).
Answer
Nucleus → DNA / control. Mitochondrion → respiration / energy. Ribosome → protein synthesis. Cell membrane → controls movement of substances.
Examiner tip
"Powerhouse" alone isn't enough for mitochondria — Cambridge wants "site of (aerobic) respiration" or "releases energy".
Question
Place these in order from smallest to largest: organ, tissue, organism, cell, organ system.
Step-by-step solution
Step 1
Cells (smallest) → tissues (groups of similar cells with a function) → organs (different tissues working together) → organ systems (organs cooperating) → organism (whole living thing).
Answer
Cell → tissue → organ → organ system → organism.
Question
List THREE structures found in plant cells but NOT in typical animal cells, and give the function of each.
Step-by-step solution
Step 1
Cellulose cell wall: rigid, gives shape and support to the cell.
Step 2
Chloroplasts: contain chlorophyll, site of photosynthesis.
Step 3
Large permanent vacuole (sap vacuole): contains cell sap, helps maintain turgor pressure for support.
Answer
Cell wall (support), chloroplasts (photosynthesis), large permanent vacuole (turgor / storage).
Question
Describe the structures found in a bacterial cell, and state two ways it differs from a plant cell.
Step-by-step solution
Step 1
A bacterial cell has a cell wall (giving shape), a cell membrane (controlling entry/exit), and cytoplasm containing ribosomes (for protein synthesis).
Step 2
Its genetic material is a single loop of circular DNA, free in the cytoplasm, and it may also have small extra rings of DNA called plasmids.
Step 3
Difference 1: a bacterial cell has NO nucleus (its DNA is free in the cytoplasm), whereas a plant cell has a true nucleus.
Step 4
Difference 2: a bacterial cell has no chloroplasts and no large permanent vacuole and no mitochondria, whereas a plant cell has all three.
Answer
Bacterial cell: cell wall, cell membrane, cytoplasm, ribosomes, circular DNA and (often) plasmids. Unlike a plant cell, it has no nucleus (DNA is free/circular) and no chloroplasts, mitochondria or large permanent vacuole.
Examiner tip
Syllabus 2.1.2 lists exactly: cell wall, cell membrane, cytoplasm, ribosomes, circular DNA, plasmids. The defining difference is 'no nucleus'.
Question
Three cells are described. Cell X has a cell wall, a large permanent vacuole and chloroplasts. Cell Y has a cell membrane but no cell wall and no chloroplasts. Cell Z has a cell wall and circular DNA but no nucleus. Identify each cell type and justify your choice.
Step-by-step solution
Step 1
Cell X has a cellulose cell wall, a large permanent vacuole AND chloroplasts — all three are features unique to plants, so it is a plant cell.
Step 2
Cell Y has no cell wall and no chloroplasts, and a flexible cell membrane only — these are features of an animal cell.
Step 3
Cell Z has a wall but its genetic material is circular DNA with NO nucleus — the absence of a nucleus is the defining feature of a bacterial (prokaryote) cell.
Answer
X = plant cell (wall + vacuole + chloroplasts); Y = animal cell (membrane only, no wall/chloroplasts); Z = bacterial cell (wall but circular DNA, no nucleus).
Examiner tip
Reasoning matters: a cell wall alone does not prove 'plant' — plant, fungal and bacterial cells all have walls. Use chloroplasts + large vacuole for plant, and 'no nucleus' for bacteria.
Question
Using the leaf as an example, explain how the levels of organisation from cell to organism apply.
Step-by-step solution
Step 1
Cell: a palisade mesophyll cell is a single specialised cell, packed with chloroplasts for photosynthesis.
Step 2
Tissue: many palisade cells working together form the palisade mesophyll tissue (a group of similar cells with a shared function).
Step 3
Organ: the leaf is an organ — it contains several different tissues (palisade, spongy mesophyll, epidermis, xylem and phloem) working together to carry out photosynthesis.
Step 4
Organ system: the leaf is part of the shoot system (the leaves, stem and buds) — a group of organs working together. Organism: the whole plant is the organism.
Answer
Palisade cell (cell) → palisade mesophyll (tissue) → leaf (organ) → shoot system (organ system) → whole plant (organism). Each level is built from the level below.
Examiner tip
The leaf is the standard 'organ' example because it clearly contains several tissue types. Naming a specific tissue and a specific cell shows full understanding.
High-scoring sample answers for cell structure and organisation on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
State the function of the cell membrane. (1 mark)
Model answer
The cell membrane controls which substances enter and leave the cell (it is selectively/partially permeable).
Why this scores
One mark for 'controls movement of substances in/out'. 'Holds the cell together' alone does not score.
State two structures found in a plant cell that are not found in a typical animal cell. (2 marks)
Model answer
A plant cell has a cellulose cell wall and chloroplasts, which a typical animal cell does not have. (A large permanent vacuole is also accepted.)
Why this scores
Any two of: cell wall, chloroplasts, large permanent vacuole. 'Cell membrane' is NOT accepted — animal cells have one too.
Describe the functions of the nucleus, the mitochondria and the ribosomes in a cell. (3 marks)
Model answer
The nucleus contains the genetic material (DNA) and controls the cell's activities. The mitochondria are the site of aerobic respiration, releasing energy from glucose for the cell to use. The ribosomes are the site of protein synthesis, where amino acids are joined to make proteins.
Why this scores
One mark each. For mitochondria, 'site of aerobic respiration / releases energy' is required — 'powerhouse' is not credited.
Compare a bacterial cell with a plant cell. Give two similarities and two differences. (4 marks)
Model answer
Similarities: both have a cell wall, and both have a cell membrane, cytoplasm and ribosomes. Differences: a bacterial cell has no nucleus — its genetic material is a loop of circular DNA free in the cytoplasm — whereas a plant cell has a true nucleus; and a bacterial cell has no chloroplasts (or mitochondria or large permanent vacuole), whereas a plant cell does.
Why this scores
Two valid similarities and two valid differences, each comparing both cells. 'No nucleus / circular DNA' is the key difference. A bacterial wall is not cellulose, so 'both have cellulose walls' would be wrong.
Define the terms cell, tissue, organ, organ system and organism. (5 marks)
Model answer
A cell is the basic structural and functional unit of a living organism. A tissue is a group of cells with similar structure working together to perform a particular function. An organ is a structure made up of different tissues working together to perform a particular function. An organ system is a group of organs working together to perform a particular function. An organism is a complete, individual living thing made up of one or more cells.
Why this scores
One mark per correct definition. The progression must be clear: tissue = similar cells; organ = several tissues; organ system = several organs.
Describe the structures present in a plant cell and state the function of each. (6 marks)
Model answer
A plant cell has a cellulose cell wall on the outside, which gives the cell shape and support. Just inside it is the cell membrane, which controls what enters and leaves the cell. The cytoplasm is the jelly-like region where many chemical reactions take place and where the organelles sit. The nucleus contains the genetic material (DNA) and controls the cell's activities. Chloroplasts contain chlorophyll and are the site of photosynthesis. The mitochondria are the site of aerobic respiration, releasing energy from glucose. A large permanent vacuole is filled with cell sap and helps keep the cell turgid for support, and tiny ribosomes are the site of protein synthesis.
Why this scores
Up to 6 marks for correctly named structures each paired with a correct function. A structure without its function (or vice versa) does not score the mark.
Definitions to memorise and the exact keywords mark schemes credit for cell structure and organisation answers — sharpened from recent examiner reports for the 2026 0610 sitting.
The basic unit of life — the smallest structure capable of independent life processes.
Membrane-bound structure containing DNA; controls cell activity.
Jelly-like substance inside the cell membrane where most chemical reactions take place; contains organelles.
Selectively permeable layer that controls what enters and leaves the cell.
Organelle where aerobic respiration takes place; releases energy from glucose.
Tiny organelle where protein synthesis occurs.
Organelle containing chlorophyll; site of photosynthesis (plant cells only).
Large fluid-filled sac in plant cells containing cell sap; provides turgor pressure for support.
Rigid outer layer of plant cells made of cellulose; gives shape and support.
In a bacterial cell, the genetic material is a single loop of circular DNA free in the cytoplasm; plasmids are small extra rings of DNA.
A group of cells with similar structures, working together to perform a shared function.
Example
Muscle tissue, xylem tissue, epithelial tissue.
A structure made up of different tissues working together to perform specific function(s).
Example
Heart, leaf, kidney.
A group of organs working together to perform a specific function.
Example
Digestive system: mouth, oesophagus, stomach, intestines, etc.
The traps other students keep falling into on cell structure and organisation questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
Why it happens
Both have a cell membrane; students conflate them.
How to avoid it
ANIMAL cells: only cell MEMBRANE (flexible). PLANT cells: cell wall (cellulose, rigid) + cell membrane (just inside the wall).
Why it happens
It's the popular phrase.
How to avoid it
Cambridge wants "site of aerobic respiration" or "releases energy from glucose". 'Powerhouse' is too vague for marks.
Why it happens
Both involve multiple tissues.
How to avoid it
Organ: ONE structure (heart). Organ SYSTEM: multiple organs working together (circulatory system: heart + blood vessels + blood).
Why it happens
Most cells students learn first (plant, animal) have a nucleus.
How to avoid it
Bacteria are prokaryotes: NO nucleus. Their DNA is a loop of circular DNA free in the cytoplasm, sometimes with plasmids.
The things students keep getting wrong in this sub-topic, answered.