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Understanding command words is essential for exam success. Each command word tells you exactly what the examiner expects in your answer. Misinterpreting a command word is one of the most common reasons students lose marks. This lesson covers every command word used in the Edexcel A-Level Biology (9BI0) specification and explains how mark schemes work.
Every exam question begins with (or contains) a command word that instructs you on the type and depth of answer required. Giving a description when the question asks for an explanation, or explaining when it asks you to evaluate, will cost you marks -- even if your biology is correct.
Exam Tip: Before writing anything, underline the command word in the question. This simple habit can prevent you from misinterpreting what is being asked.
What it means: Give the precise meaning of a term.
What examiners look for: A concise, accurate definition using correct scientific terminology.
Example:
Exam Tip: Learn definitions word-for-word from the specification. Examiners mark against precise wording -- for example, 'water molecules' (not just 'water') and 'partially permeable membrane' (not 'semi-permeable membrane' for Edexcel).
What it means: Give a brief, factual answer. No explanation is needed.
What examiners look for: A short, direct answer -- often a single word, phrase, or sentence.
Example:
What it means: Give an account of what something is like, how something works, or what happens. No explanation of why is needed.
What examiners look for: A detailed account that covers key features, stages, or observations in a logical order.
Example:
What it means: Give reasons for something. Say why or how something happens.
What examiners look for: A clear chain of reasoning that links cause to effect. Use words like 'because', 'therefore', 'this means that', 'as a result'.
Example:
Exam Tip: For 'explain' questions, every mark typically requires a because statement. If a question is worth 3 marks, you should aim for at least three linked points of reasoning.
What it means: Use your biological knowledge to propose an explanation or answer for something that you may not have been directly taught. There may be more than one acceptable answer.
What examiners look for: A plausible explanation that demonstrates understanding of relevant biological principles, applied to an unfamiliar context.
Example:
What it means: Consider the evidence, arguments, or information provided and reach a justified conclusion. Weigh up strengths and weaknesses, advantages and disadvantages, or evidence for and against.
What examiners look for: A balanced discussion that considers both sides followed by a clear conclusion supported by evidence.
Example:
What it means: Identify similarities and differences between two or more things.
What examiners look for: Direct, paired comparisons -- not separate descriptions of each thing.
Example:
Exam Tip: When asked to 'compare', always use comparative language: 'whereas', 'while', 'in contrast', 'both', 'similarly'. A comparison must address both things in the same sentence or point, not describe them separately.
What it means: Break down information, data, or a situation into its component parts and examine how they relate to each other.
What examiners look for: Identification of trends, patterns, or relationships in data, with specific reference to figures and units.
Example:
What it means: Give reasons to support a conclusion or decision.
What examiners look for: Evidence-based reasoning that supports a particular viewpoint or answer.
What it means: Give the main points or key features without excessive detail.
What examiners look for: A brief but accurate summary covering the essential points.
What it means: Work out a numerical answer using the data provided. You must show your working.
What examiners look for: Clear working, correct substitution into formulae, correct units, and an answer to an appropriate number of significant figures.
Exam Tip: Always show your working in calculation questions. Even if your final answer is wrong, you can gain marks for correct method. Always include units in your final answer.
Mark schemes are the documents examiners use to award marks. Understanding how they work can significantly improve your exam technique.
| Type | Description | Example |
|---|---|---|
| Mark point (MP) | A specific fact, idea, or step that earns a mark | 'DNA helicase unwinds the double helix' |
| Linked marks | A mark that can only be awarded if a previous mark point has been given | 'Accept "hydrogen bonds broken" only if "between bases" is given' |
| Quality of Written Communication (QWC) | Marks for clarity, coherence, and use of scientific terminology | 'Answer is well-organised with correct use of terminology' |
| Allow/Accept | Alternative correct answers that the examiner will credit | 'Accept "partially permeable" or "selectively permeable"' |
| Reject | Answers that will not be credited, even if partially correct | 'Reject "semipermeable"' |
| Ignore | Information that is neither credited nor penalised | 'Ignore references to active transport' |
For extended response questions (usually 6 marks), examiners use a levels-based approach:
| Level | Marks | Descriptor |
|---|---|---|
| Level 3 | 5--6 | Comprehensive and relevant answer with logical structure and correct terminology |
| Level 2 | 3--4 | Most relevant information covered with some logical structure |
| Level 1 | 1--2 | Some relevant information but limited structure or terminology |
| 0 | 0 | No relevant information |
Exam Tip: For 6-mark questions, examiners first decide which level your answer falls into, then fine-tune the mark within that level. To reach Level 3, your answer must be comprehensive, logically structured, and use correct scientific terminology throughout.
| Mistake | Example | Correction |
|---|---|---|
| Describing when asked to explain | 'The enzyme changes shape' | 'The enzyme changes shape because high temperature breaks hydrogen bonds, altering the active site' |
| Not comparing directly | 'Mitosis produces 2 cells. Meiosis produces 4 cells.' | 'Mitosis produces 2 diploid cells, whereas meiosis produces 4 haploid cells' |
| Missing the 'justify' element | Stating a conclusion without evidence | 'The student should use method B because it has a lower percentage error (2.1% vs 5.3%)' |
| Not showing working in calculations | Writing only the final answer | Show every step: formula, substitution, calculation, unit |
Command words are not decoration -- they are coded instructions about how the examiner will award the marks. Each command word encodes three things at once: the assessment objective the question targets (AO1 recall, AO2 application, or AO3 analysis/evaluation), the depth the answer must reach (a single fact versus a chain of reasoning versus a balanced judgement), and the verbal moves the answer must contain (linking phrases, comparative grammar, data quotations, conclusions). A candidate who ignores the command word and writes a generic "biology answer" leaves marks on the table even when the underlying biology is correct, because the mark scheme is not searching for biology -- it is searching for the specific structural features the command word demands.
The strategic insight that separates B-grade work from A and A* work is that command words are the interface between the student's biology and the mark scheme's bullet points. Master that interface and the same biological knowledge converts to roughly 15--20% more marks across the qualification. The sections below take the command-word vocabulary, decompose how mark schemes are written, walk through three high-yield command words in detail, and end with a worked specimen-format question marked sentence-by-sentence so you can see the gap between an answer and the marks it earns.
The command words used by Pearson Edexcel on 9BI0 cluster into three tiers by the assessment objective they target. Tier 1 command words ask for recall and basic communication of subject knowledge -- the AO1 territory. Tier 2 command words ask for application of knowledge to familiar or unfamiliar contexts -- the AO2 territory. Tier 3 command words ask for analysis, evaluation and judgement on data or arguments -- the AO3 territory. The same vocabulary appears across all three papers, but the proportions shift: Papers 1 and 2 lean Tier 1 and Tier 2, while Paper 3 leans Tier 2 and Tier 3.
| Command word | Tier (dominant AO) | Typical mark range | What the answer must contain |
|---|---|---|---|
| State | Tier 1 (AO1) | 1--2 | A single phrase or sentence; no elaboration |
| Name | Tier 1 (AO1) | 1 | One named entity -- a structure, molecule, organism |
| Identify | Tier 1 (AO1) | 1--2 | Pick out the correct item from a list, figure or stem |
| Define | Tier 1 (AO1) | 1--2 | Precise specification wording, no examples |
| Describe | Tier 1 (AO1) | 2--6 | Sequence of features, stages or observations; no causation |
| Outline | Tier 1 (AO1) | 2--4 | Main points only, no secondary detail |
| Label | Tier 1 (AO1) | 1--3 | Annotate a diagram with named structures |
| Explain | Tier 2 (AO1+AO2) | 2--6 | Causal chain using because, therefore, as a result |
| Calculate | Tier 2 (AO2) | 1--4 | Working shown, correct substitution, units, sig figs |
| Apply | Tier 2 (AO2) | 2--4 | Use named principle in the unfamiliar context given |
| Compare | Tier 2 (AO2) | 2--6 | Paired similarities AND differences using whereas, both |
| Predict | Tier 2 (AO2) | 1--3 | A specified outcome backed by a brief reason |
| Plot | Tier 2 (AO2) | 2--4 | Axes, scale, points, line of best fit drawn correctly |
| Determine | Tier 2 (AO2) | 1--4 | Numerical answer extracted from data, working shown |
| Suggest | Tier 3 (AO2+AO3) | 2--4 | Plausible explanation in unfamiliar context; multiple answers may score |
| Analyse | Tier 3 (AO3) | 3--6 | Trends, patterns and relationships in data, with figures quoted |
| Evaluate | Tier 3 (AO3) | 4--9 | Balanced for/against argument plus a justified conclusion |
| Justify | Tier 3 (AO3) | 2--4 | Reasons supporting a stated conclusion, evidence-grounded |
| Discuss | Tier 3 (AO3) | 4--9 | Multiple perspectives weighed; usually with a closing position |
| Comment on | Tier 3 (AO3) | 2--4 | Brief evaluative observation tied to specific data feature |
| Deduce | Tier 3 (AO2+AO3) | 2--4 | Conclusion reached from evidence in the stem |
A useful mental partition is to ask, before writing, which tier is this word asking for? If Tier 1, the answer is short and crisply worded; spending eight lines on a 2-mark state question is wasted time. If Tier 2, the answer must visibly link cause to effect or apply principle to context. If Tier 3, the answer must engage with evidence -- either by quoting data or by considering alternatives -- and reach a conclusion.
A common pattern in mark schemes is for Tier 1 command words to attract a single rewardable phrase per mark, Tier 2 command words to attract a because-clause per mark, and Tier 3 command words to attract a balanced argument plus a closing judgement for the highest level. That is why the same 4-mark question can demand four crisp facts (if it is a describe) or two paired strengths and weaknesses plus a conclusion (if it is an evaluate) -- and why writing the wrong shape costs marks.
Edexcel mark schemes for 9BI0 follow a consistent internal architecture. Understanding this architecture lets you reverse-engineer the marks before you write, rather than hoping the examiner will be generous after you write.
A short-answer mark scheme (typically 1--6 marks) lists rewardable points as bullets. Each bullet is a specific idea, sometimes with alternative wordings the examiner will credit. Around each bullet sit three structural cues:
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