IGCSE Biology Command Words Decoded: What Examiners Actually Want

The full command-word reference table

These are the command words you will meet across Papers 1–6, with what each one obliges you to do:

Train the habit of underlining the command word before reading anything else in the question. It sets the contract your answer must fulfil.

Describe vs explain: the distinction worth the most marks

No pair of command words costs IGCSE Biology students more marks than these two, because everyday English treats them as near-synonyms. Cambridge does not.

Describe = what. "Describe the effect of temperature on enzyme activity" wants the pattern: activity increases as temperature rises to about 37 °C, peaks at the optimum, then decreases rapidly above it. Notice. No reasons at all, and full marks are available without any.

Explain = why or how. "Explain the effect of temperature on enzyme activity" wants mechanism: higher temperatures give molecules more kinetic energy, so substrate and enzyme collide more often; above the optimum the enzyme is denatured. The active site changes shape, so the substrate no longer fits.

The two failure modes are mirror images:

• Asked to describe a graph, the student writes a mechanism essay and never actually states the trend. The only thing being marked.
• Asked to explain, the student restates what happens in different words and never reaches a single because.

A self-check that works: in an explain answer, every marking point should be attachable to the word "because" or "so". In a describe answer of data, you should be quoting directions, comparisons and figures from the material. When a question says describe and explain, it wants both. Structure your answer in two visible parts. This distinction is also the backbone of our SCORE method for 6-mark questions.

"Suggest": the question type you cannot revise for: but can prepare for

Suggest deserves its own section because it behaves differently from every other command word. It signals that the answer is not directly in the syllabus: you are being asked to apply familiar principles to an unfamiliar organism, experiment or data set. Paper 4 and Paper 6 lean on it heavily, and it is precisely where students who memorised notes hit a wall.

Example: "A fish living in fast-flowing rivers has a larger gill surface area than a similar species in still water. Suggest why." You have never revised this fish. But you have revised the principles of gas exchange: active swimming demands more respiration, more respiration demands more oxygen uptake, and a larger surface area increases the rate of diffusion. Assemble those, and you have full marks on an animal you met thirty seconds ago.

How to get better at it:

• Anchor every answer to a core principle: surface area to volume ratio, diffusion gradients, enzyme specificity, competition, natural selection. Suggest questions are core principles wearing costumes.
• Accept reasonable uncertainty. Mark schemes for suggest questions accept any biologically sound answer, often listing alternatives. You are not hunting one sacred sentence.
• Never leave it blank. Credit is available for sensible reasoning even when your answer differs from the scheme's examples.

Students who reframe suggest from "trick question" to "open-book question about principles I know" stop fearing the hardest marks on the paper.

Compare, calculate and the data words

Compare has a structural rule examiners enforce strictly: every point must reference both subjects. "Arteries have thick walls" earns nothing in a compare question; "arteries have thicker walls than veins" earns the point. Comparative language, thicker, faster, higher, whereas, both: is the tell of a creditable answer. Writing two separate descriptive paragraphs, one per subject, is the classic zero-structure error.

Calculate appears throughout the qualification: percentage change, magnification, rates from graphs. The discipline:

1. Show working: method marks survive arithmetic slips.
2. Include units unless the answer line provides them (and note magnification has no units).
3. Match the requested precision: "to one decimal place" or "to the nearest whole number" instructions are mark-bearing.

The everyday formulas: percentage change = (final − initial) ÷ initial × 100; magnification = image size ÷ actual size, with both in the same units: millimetre-to-micrometre conversion errors (×1000) are a perennial mark-killer.

Identify and predict are data words: the answer is in (or follows directly from) the material on the page. For identify, point precisely. Quote the reading, name the labelled structure. For predict, extend the visible pattern and, where the marks suggest it, add the principle behind your prediction. On Paper 6 especially, these words reward students who read tables and graphs slowly and answer from the data, not from memory. A habit covered in depth in our Paper 6 guide.

Reading the whole question stem: marks, context and scope

The command word sets the task; the rest of the stem sets the boundaries. Three more reading habits that protect marks:

• The mark allocation is the answer's blueprint. [1] wants one fact. [3] wants three distinct creditable points. A five-line answer to a one-mark question wastes time; a one-line answer to a four-mark question abandons three marks. Match points to marks, every time.
• Context is not decoration. When a question describes a specific scenario, a named plant in a salty soil, an athlete mid-sprint, the mark scheme expects your answer in that context. Generic textbook answers that ignore the scenario routinely drop marks. If the question mentions photosynthesis in a shaded greenhouse, your limiting-factor answer must engage with light.
• Scope words narrow the field. "Other than…", "using only the data…", "in this investigation…" are exclusion instructions. "Give one difference, other than wall thickness, between arteries and veins" makes wall thickness worth zero. Yet students supply it constantly.

A practical drill: for one week, before answering any practice question, annotate it. Circle the command word, box the mark count, underline scope restrictions. It feels slow for three days; then it becomes automatic, and a whole category of avoidable errors disappears. More of these recurring traps are catalogued in our common exam mistakes guide.

Make command-word discipline automatic

Knowing these definitions is the easy half. The hard half is honouring them at speed, in minute 60 of Paper 4, when the pressure pushes you back towards writing everything you know. That gap between knowing and doing closes only through marked practice. Answering real questions, then having someone hold your answer against the command word's actual demand.

This is bread-and-butter work for our team of experienced Biology specialists. In 1-to-1 sessions they run command-word drills on past-paper questions: you answer, they mark as Cambridge would, and the feedback is specific, "this was a describe answer to an explain question; here is the because-chain it needed." Students typically find that one or two command words account for most of their leaked marks, so the fix is fast and personal rather than generic.

Classes are online across Malaysia, 1.5 hours at RM80/hour, with tutors handpicked by our founder Rig for Cambridge IGCSE experience. It all starts with a free 1-hour trial taught by your assigned tutor. Bring a marked past paper, and the trial itself will show you which command words are quietly costing you marks. From there, both sides decide whether to continue. No risk, genuine diagnosis.