Why Biology is keyword-heavy
Pure Biology is the most vocabulary-dependent of the O-Level Pure Sciences. Mark schemes reward the right word in the right context: "transpiration" not "evaporation from the leaf", "active transport" not "energy-using movement", "stomata" not "tiny holes on the leaf surface". Synonyms and paraphrasing typically lose marks even when the underlying logic is correct.
Topic-by-topic keyword priorities
- Cells & transport — diffusion, osmosis, active transport, partially permeable membrane, water potential, concentration gradient.
- Nutrition (plants) — photosynthesis, chlorophyll, palisade mesophyll, stomata, guard cells, transpiration, xylem.
- Nutrition (humans) — peristalsis, villi, microvilli, surface area, enzymes (amylase, pepsin, trypsin, lipase).
- Transport in humans — atrium, ventricle, semilunar valve, oxygenated, deoxygenated, plasma, platelets.
- Respiration — aerobic, anaerobic, lactic acid, oxygen debt, mitochondria, ATP.
- Excretion & homeostasis — ultrafiltration, selective reabsorption, ADH, hypothalamus, vasoconstriction, vasodilation.
- Inheritance — allele, gene, genotype, phenotype, homozygous, heterozygous, dominant, recessive.
- Ecology — producer, consumer, decomposer, trophic level, biomass, food chain, food web, ecosystem.
The Biology CER pattern
Biology OEQs typically have a longer reasoning section than Physics or Chemistry. The structure usually unfolds as:
- Claim — what happens (the observable outcome)
- Evidence — what triggers it from the question
- Reasoning step 1 — the immediate biological mechanism
- Reasoning step 2 — the downstream consequence
- Reasoning step 3 (if needed) — the overall purpose or effect
Worked example
Question (4 marks): "Explain how the structure of a plant root is suited to its function of absorbing water."
Strong answer:
- The root has root hair cells with a long, thin shape that increases the surface area for water absorption [1].
- The cell wall is thin, providing a short diffusion distance for water to enter [1].
- Water moves into the root hair cell by osmosis, from the soil (higher water potential) to the cytoplasm (lower water potential) across the partially permeable membrane [1].
- The water then passes from cell to cell through the cortex, eventually reaching the xylem, which transports it up the plant [1].
Notice: every mark is tied to a specific keyword or phrase. Paraphrasing — "the membrane lets water through" instead of "partially permeable membrane via osmosis" — loses marks.
Common mark traps in Biology OEQ
- Saying "kills" instead of "denatures" for enzyme questions. Enzymes denature; they don't die.
- "Water enters" instead of "water enters by osmosis". The mechanism word is the mark.
- Skipping the "what for" step in adaptation questions. "Long root hair = more absorption" needs both the structure AND the function-purpose link.
- Mixing up active transport and diffusion. If the question mentions "against the gradient" or "energy required", it's active transport. Otherwise check the context carefully.
How to drill Biology OEQ
Build a single A4 keyword sheet per topic. Practise recall from the topic name: see "Excretion", write all 15 keywords. Then take past-year OEQs on that topic and answer them with the keyword sheet visible. Then redo without it. The combination of vocabulary drill + structured answering is what moves students up.
For the underlying structure, see CER structure deep dive. For Physics OEQ specifically (different rhythm), see Physics OEQ — formulas + reasoning. For broader OEQ technique, see the pillar post how to score better on open-ended questions for O-Level Science.