You are viewing a free preview of this lesson.
Subscribe to unlock all 10 lessons in this course and every other course on LearningBro.
Command words are the instruction verbs at the start of a question — state, describe, explain, calculate, compare, evaluate and so on. They tell you exactly what kind of answer the examiner wants and how much to write. Misreading or ignoring the command word is one of the most common reasons students lose marks across all three sciences: two candidates can know identical science, but the one who responds correctly to the command word scores higher. Because Combined Science A spans biology, chemistry and physics, the same command word can feel very different depending on the paper — yet what it demands never changes.
By the end of this lesson you should know the command words OCR uses, be able to recognise what each demands, apply them across all three sciences, and avoid the two classic traps — describe versus explain and compare versus contrast.
Reading the command word tells you which AO a question targets — state/describe usually signal AO1, explain/calculate/suggest signal AO2, and evaluate/justify signal AO3 — so this technique underpins all three objectives.
| Command word | What it asks for | What to write |
|---|---|---|
| State / Name / Give / Identify | A short fact, no explanation | A word or short phrase |
| Define | The precise scientific meaning of a term | A concise, exact definition |
| Describe | What happens or what the data shows | An ordered account of features, steps or trends — no reasons |
| Explain | What happens and why | A linked chain of reasoning with "because"/"so" |
| Compare | Similarities and differences | Explicit, linked point-by-point comparisons |
| Suggest | Apply knowledge to an unfamiliar context | A reasonable, scientific response using the given information |
| Calculate | Work out a numerical value | Formula, substitution, working and answer with units |
| Determine | Use given data or a calculation to find a value | Working that leads to the value the data imply |
| Estimate | A rough but reasoned value | A sensible figure with brief justification |
| Predict | Say what will happen | An expected outcome, often with a short reason |
| Evaluate | Strengths and weaknesses, then a conclusion | A balanced judgement supported by evidence |
| Justify | Reasons supporting a decision or conclusion | The decision plus the evidence/reasoning for it |
| Plot / Draw / Sketch / Label | Produce or annotate a graph or diagram | Accurate points/lines/labels; a ruler where straight lines are needed |
The sections below give a precise meaning and examples drawn from all three sciences for the most important command words.
Exam Tip: Before writing anything, underline the command word. It forces you to check what is actually being asked and sets the depth and style of your answer.
Meaning: write a short, factual answer. No explanation is needed. Usually 1 mark.
Exam Tip: If the word is state or name, keep it to a word or short phrase. A long explanation wastes time and can introduce an error that contradicts your correct answer.
Meaning: give the exact scientific meaning of a term. Usually 1–2 marks.
Exam Tip: OCR definitions are marked on specific key words. Forgetting "partially permeable membrane" for osmosis, or "same number of protons" for isotopes, can cost the mark even though the rest is right.
Meaning: say what happens, or what the data shows — an ordered account of the main features, steps or patterns. Do not give reasons. Usually 2–4 marks.
Exam Tip: When describing data, quote figures. "The rate increases" is weak; "the rate increases from 5 cm³/min at 20 °C to 18 cm³/min at 40 °C" is a describe answer that scores.
Meaning: say what happens and why — give reasons or mechanisms, not just an account. Usually 2–6 marks.
Exam Tip: The single most common command-word error is describing when asked to explain. Make sure every explain answer contains a reason — signalled by "because", "this means that" or "so".
Meaning: give similarities AND differences between two or more things, using explicit linking language. Usually 2–4 marks.
A genuine comparison links the two things in each point ("A does X, whereas B does Y"). Listing features of one, then separately listing features of the other, is weaker and often loses marks because the examiner has to do the comparing for you.
Exam Tip: Compare is not the same as contrast. Contrast asks for differences only; compare asks for both similarities and differences. Use both, whereas, however, similarly, unlike to make each comparison explicit.
Meaning: apply your knowledge to a new or unfamiliar situation. There may be more than one acceptable answer. Usually 1–3 marks.
Subscribe to continue reading
Get full access to this lesson and all 10 lessons in this course.