Shared organelles + three plant-only
Both animal and plant cells contain: nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells add three: a cell wall (outside the membrane), chloroplasts and a permanent vacuole of cell sap. These plant-only structures — WCV (Wall, Chloroplast, Vacuole) — are what comparison questions test. Animal cells may have small temporary vacuoles, but only the plant permanent vacuole counts as a distinct structure here.
Organelle functions need the key word
Learn each function in the mark scheme's two-element form. Nucleus — DNA (genetic information) that controls the cell's activities. Mitochondria — aerobic respiration, releasing energy as ATP. Ribosomes — protein synthesis. Cell membrane — controls entry and exit, selectively permeable. Plant-only: cell wall (support), chloroplasts (photosynthesis), vacuole (turgor). 'Controls the cell' or 'gives energy' without the key word scores one of two marks.
Magnification = image ÷ actual size
Magnification — a pure number, no units. Cells are in micrometres (1 mm = 1000 µm), so if the image is in mm and the cell in µm, convert first. Example: image 24 mm, actual 40 µm → 24 mm = 24 000 µm, . A value below 1 means you skipped the conversion; a magnified image gives . To find actual size: actual = image ÷ M. Always show working — the method earns marks even if the arithmetic slips.
Drawn from real examiner reports.
Convert mm to µm before dividing
The costliest magnification error is dividing an image in mm by an actual size in µm without converting — the answer is out by 1000. Put both in the same unit first: a mm image ×1000 gives µm. In June 2024 Paper 1BR Q2(b)(i) candidates also had to round to the nearest whole number; a common error was dividing correctly but not rounding.
June 2024 Paper 1BR Q2(b)(i) — candidates had to convert mm to µm and round to the nearest whole number; a common two-marks-only error was correct division without the required rounding.
Animal cells have no cell wall
Animal cells never have a cell wall — it is a plant-only structure (also in bacteria and fungi). The cell membrane, by contrast, is present in BOTH animal and plant cells, and in a plant cell it lies just inside the wall. Two errors lose marks: saying animal cells have a wall, and saying a plant cell has a wall 'instead of' a membrane — plant cells have both.
Say alveolar wall, not cell wall
'Cell wall' is a precise term for the cellulose layer around a plant cell. In June 2024 Paper 1BR Q3(b)(iii) candidates wrote 'cell wall' when they meant the alveolar wall, losing the mark for imprecise cell-structure vocabulary. Name the actual structure the question is about — alveolar wall, capillary wall, cell membrane — rather than defaulting to 'cell wall'.
June 2024 Paper 1BR Q3(b)(iii) — candidates wrote 'cell wall' for the alveolar wall, showing imprecise cell-structure terminology.
The nucleus does not make proteins
A frequent slip is crediting the wrong organelle: 'the nucleus makes proteins' or 'the nucleus provides energy'. The nucleus only stores the DNA instructions. Protein synthesis happens at the ribosomes; aerobic respiration, releasing energy as ATP, happens in the mitochondria. Match each job to its own organelle.
Function without the key word
Organelle-function marks nearly always need two linked ideas. 'The nucleus controls the cell' scores one of two without 'contains DNA / genetic information'. 'Mitochondria provide energy' needs 'by aerobic respiration / releasing ATP'. 'The membrane controls what goes in and out' needs 'selectively permeable'. After the function, ask 'because of what?' and add the mechanism.
Stem cells are undifferentiated
A stem cell is unspecialised (undifferentiated): it divides by mitosis and its daughter cells then differentiate into specialised types. In November 2024 Paper 2B Q3(a) a common error was confusing differentiated with undifferentiated — describing stem cells as already specialised. A differentiated cell has a fixed structure and cannot turn into a different cell type.
November 2024 Paper 2B Q3(a) — candidates confused differentiated with undifferentiated when explaining how stem cells differ from other body cells.
Practise structure and function both ways
Cell questions run both ways: 'state the function of X' (give the two-element form) and 'name the organelle that does Y' (site of respiration → mitochondria). Drill both. A table of organelle / animal? / plant? / function covers every version.
Comparisons: pick from WCV
For 'give two differences between plant and animal cells', always choose from the plant-only list WCV — cell Wall, Chloroplasts, permanent Vacuole. These are structural and score. Avoid non-structural differences such as 'plants are green' or size, which earn nothing.
Show magnification working
In a magnification calculation, write the formula, substitute with the unit conversion shown, then give the final value as a plain number with no unit. Round exactly as the question asks. Method marks survive an arithmetic slip, so never leave the answer space blank.
All living cells share some common features, but plant and animal cells differ in three key structures.
Structures present in BOTH animal and plant cells:
| Organelle | Function |
|---|---|
| Nucleus | Contains deoxyribonucleic acid (DNA) that carries genetic information and controls the activities of the cell |
| Cytoplasm | Fluid medium where most of the cell's chemical reactions take place |
| Cell membrane | Controls what passes into and out of the cell (selectively permeable) |
| Mitochondria | Site of aerobic respiration; releases energy as adenosine triphosphate (ATP) for the cell |
| Ribosomes | Site of protein synthesis (where amino acids are joined to make proteins) |
Structures found ONLY in plant cells (not in animal cells):
| Organelle | Function |
|---|---|
| Cell wall | Made of cellulose; provides strength and support; prevents bursting when water enters by osmosis |
| Chloroplasts | Contain chlorophyll; site of photosynthesis where light energy is absorbed to make glucose |
| Permanent vacuole | Filled with cell sap; maintains turgor pressure and gives structural support to the plant |
Memory hook: Plant-only structures = WCV (Wall, Chloroplasts, Vacuole).
State the function of the nucleus.
The table below lists functions of cell structures.
| Function | Name of structure |
|---|---|
| Contains DNA and controls cell activities | |
| Site of aerobic respiration | |
| Site of protein synthesis | |
| Controls what enters and leaves the cell |
Complete the table by naming each structure. (4 marks)
