Command terms
What each command term asks for, how marks relate to the number of points, and how strong and weak answers differ on the same biology.
- IB Biology
- Exam skills
- SL and HL
Almost every written question in IB Biology is built around a command term: a word or phrase such as state, outline, explain or evaluate. The command term sets the kind of answer that earns marks, and the number of marks in square brackets sets how much of it is needed. Reading both before writing anything is the quickest way to stop losing marks for answers that are correct but of the wrong kind.
The same piece of biology can be asked about with a 1-mark "state" or a 6-mark "explain". Both questions draw on the same facts, but the 6-mark question needs far more of the reasoning to be written down.
What a command term tells you
Command terms can be grouped by the assessment objective they test. Objective 1 terms ask for knowledge and understanding: recalling a fact, a definition or a diagram. Objective 2 terms ask you to apply that knowledge: calculate, describe, outline, distinguish. Objective 3 terms ask you to formulate, analyse and evaluate: explain, deduce, suggest, discuss. Questions using objective 3 terms usually carry more marks, and they are where most marks are lost.
Markschemes award one mark per valid, distinct point, up to a stated maximum. The mark allocation is therefore a guide to the number of separate points to make. A 3-mark "explain" needs three linked points; writing one point three times in different words scores one mark.
Objective 1: knowledge and understanding
These terms ask for recall. Answers are short and need no reasoning, but they must be precise: a single wrong word in a definition can lose the mark.
Command term | Meaning | What a full-mark answer looks like |
|---|---|---|
Define | Give the precise meaning of a word, phrase or quantity. | One accurate sentence using the correct technical terms. "Osmosis: the net movement of water across a partially permeable membrane from higher to lower water potential." |
Draw | Represent by a labelled, accurate diagram or graph, using a pencil. | Single clear lines, correct proportions, every structure the question names, labels with ruled lines. Graphs: points plotted correctly and joined by a straight line or smooth curve. |
Label | Add labels to a diagram. | The correct name on each indicated structure, with nothing extra that could contradict it. |
List | Give a sequence of brief answers with no explanation. | Separate items, one per line, exactly as many as asked. "List three functions of the liver." |
Measure | Obtain a value for a quantity. | A reading with its unit, taken to the precision of the instrument or ruler. |
State | Give a specific name, value or other brief answer without explanation. | A word, phrase or number. "State the product of glycolysis": pyruvate. |
Objective 2: application
These terms ask you to use what you know: to process numbers, to describe data or a process in order, or to separate two ideas clearly.
Command term | Meaning | What a full-mark answer looks like |
|---|---|---|
Annotate | Add brief notes to a diagram or graph. | Short notes beside labels that say what a structure does or what part of a curve shows. "Atrioventricular valve: closes to prevent backflow of blood into the atrium." |
Apply | Use an idea, equation, principle or rule in a new situation. | The rule stated and then used with the new data, for example the Lincoln index applied to a new capture survey. |
Calculate | Obtain a numerical answer showing the relevant stages in the working. | Formula, substitution, answer with unit and sensible precision. A correct answer with no working may lose a mark. |
Describe | Give a detailed account. | What happens or what the data show, in order, with values and units: the trend, any turning point and the range. No reasons. |
Distinguish | Make clear the differences between two or more concepts or items. | Paired differences only. "Active transport uses ATP; simple diffusion does not." |
Estimate | Obtain an approximate value. | A value with its unit, reached by a stated method (for example by counting squares under a scale bar). |
Identify | Provide an answer from a number of possibilities. | The single correct choice: the stage of mitosis in a micrograph, the trophic level, the independent variable. |
Outline | Give a brief account or summary. | Short points in a logical order, one per mark. "Outline the stages of PCR": denaturation, annealing of primers, extension. |
Describe and outline are often confused. An outline is a brief summary of the main steps; a description gives a fuller account with detail, values or features at each step. Neither asks for reasons.
Objective 3: formulate, analyse and evaluate
These terms ask you to reason: to give causes, reach conclusions, weigh evidence or propose answers to unfamiliar problems.
Command term | Meaning | What a full-mark answer looks like |
|---|---|---|
Analyse | Break down in order to bring out the essential elements or structure. | The trends, anomalies and relationships in a data set, each stated with values. |
Comment | Give a judgement based on a given statement or result of a calculation. | A judgement with a reason. "The standard deviations overlap, so the difference between the means may not be significant." |
Compare | Give an account of the similarities between two or more items, referring to both throughout. | Similarities stated for both items. Markschemes for compare often credit differences too, so giving both is safe. |
Compare and contrast | Give an account of similarities and differences between two or more items, referring to both throughout. | Paired statements of similarities and differences, often best set out as a table. |
Construct | Display information in a diagrammatic or logical form. | A Punnett grid, cladogram, food web or dichotomous key, complete and correctly laid out. |
Deduce | Reach a conclusion from the information given. | The conclusion and the piece of evidence it follows from. "Both parents must be heterozygous because two unaffected parents had an affected child." |
Design | Produce a plan, simulation or model. | A method with independent, dependent and controlled variables, how each is measured or controlled, repeats and safety. |
Determine | Obtain the only possible answer. | A single value or result, with working where it is calculated. |
Discuss | Offer a considered and balanced review that includes a range of arguments, factors or hypotheses. | Points on more than one side, each supported by evidence or reasoning, ending in a conclusion. |
Evaluate | Make an appraisal by weighing up the strengths and limitations. | Strengths and limitations of a method, model or claim, then a judgement. |
Explain | Give a detailed account including reasons or causes. | A chain of cause and effect, each step linked by "because", "so" or "therefore". |
Interpret | Use knowledge and understanding to recognise trends and draw conclusions from given information. | What a gel, pedigree or graph shows and what it means biologically. |
Justify | Give valid reasons or evidence to support an answer or conclusion. | The reason or data behind a choice. "A t-test is suitable because two means of continuous data are being compared." |
Predict | Give an expected result. | The expected outcome, often with direction and size. A short reason helps but is not always required. |
Sketch | Represent by means of a diagram or graph, labelled as appropriate, giving a general idea of the shape or relationship. | Labelled axes and the correct shape and key features (peak, plateau, intercept), without exact values. |
Suggest | Propose a solution, hypothesis or other possible answer. | A plausible answer grounded in biology and the context given. Several different answers can be accepted. |
To what extent | Consider the merits or otherwise of an argument or concept. | A weighing of evidence for and against that ends in a clear judgement of how far the claim holds. |
One piece of biology, four command terms
The effect of temperature on enzyme activity can be asked about at every level of demand. Comparing answers to the same content shows exactly what each command term adds. The graph of enzyme activity against temperature is the starting point for all four questions.
- Rate of reaction
Describe and explain: the most common confusion
Describe asks what happens; explain asks why it happens. Data questions often use both on the same graph, one after the other. A description that strays into reasons earns nothing extra, and an explanation without reasons earns no more than a description.
Compare, compare and contrast, distinguish
These three terms all deal with two or more items, and each needs statements that refer to both items. A list of features of mitosis followed by a separate list for meiosis does not count as a comparison, because the marker has to do the pairing.
Distinguish: differences only.
Compare: similarities (markschemes often credit differences as well).
Compare and contrast: similarities and differences, both required.
Evaluate, discuss and to what extent
These terms ask for a balanced answer that ends in a judgement. An answer that argues only one side cannot reach full marks, however detailed it is.
Evaluate: strengths and limitations of a method, model, claim or data set, then an overall judgement.
Discuss: a range of arguments, factors or hypotheses, each supported, then a conclusion.
To what extent: the evidence for and against a claim, then a judgement of how far it holds ("largely", "only partly").
Suggest, deduce and predict: questions about the unfamiliar
Paper 1B and Paper 2 Section A often describe an organism or experiment you have never met. Suggest, deduce and predict ask you to use biology you know in that new context. The markscheme accepts any answer that is plausible and consistent with the information given, so a reasoned guess is far better than a blank.
Suggest: propose a reason or solution. Tie it to the context: "The large error bars at 40 °C suggest the enzyme was being denatured at different rates in different repeats" earns more than "human error".
Deduce: the conclusion must follow from the data given. Quote the piece of data that leads to it.
Predict: give the expected result with its direction; a reason is good practice even when not demanded.
Draw, sketch, label and annotate
Drawing questions are marked on named features in the right places, so clarity matters as much as accuracy. Draw means an accurate, labelled diagram in pencil; sketch means the general shape with key features labelled; label means names only; annotate means names plus a short note on function or significance.
Use single, unbroken lines and no shading.
Rule label lines; make each one end exactly on the structure, and never let two cross.
Draw every feature the question names, in proportion.
For a sketch graph, label both axes with the variable and unit and show the shape: where the curve starts, where it peaks or plateaus.
The conventions for biological drawings from specimens are set out in full in Practical techniques and biological drawing.
Calculate, determine and estimate
All three ask for a number. Calculate needs the working; determine expects one correct value, often read from a graph; estimate accepts an approximate value reached by a sensible method. In every case, give the unit and a sensible number of significant figures, usually the same as the data.
A routine for every written question
Read the whole question, including the stem and any data, before answering the first part.
Underline the command term and note the marks.
Decide what kind of answer the term needs: a fact, a trend, a reason, a pair, a judgement.
Plan one distinct point per mark, plus one or two spare for larger questions.
Use the context given: name the organism, the variable or the values from the data.
Use precise terms ("denatured", "water potential", "allele"), never "it" or "this" without a noun.
Reread the command term once more before moving on.
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