What Do IB Biology Command Terms Mean and How Are Marks Awarded?

Command terms are specific verbs (state, describe, explain, discuss) that define the depth of response required. Marks are awarded against a mark scheme built around that verb — a 'state' question gives one mark per correct fact, while 'explain' needs reasoning linking cause to effect, and no marks come from correct content alone if the reasoning link is missing.

Describe asks you to give a detailed account with no reasoning required — just accurate features or a sequence of events. Explain demands you say why or how, giving reasons or causes. A description of osmosis states water moves down a gradient; an explanation says why the gradient exists.

Evaluate means weighing up strengths and limitations of a method, theory or data set to reach a supported judgement. It's the highest-demand command term in Biology and appears most in Paper 3 data-based questions and internal assessment. A one-sided answer with no judgement rarely scores full marks.

'Compare' asks for similarities only; 'contrast' asks for differences only; 'compare and contrast' requires both, stated explicitly rather than implied. Mark schemes usually award marks separately for genuine similarities and genuine differences, so a list of only differences under 'compare and contrast' loses easy marks.

Biology-specific terms include 'annotate' (add labels with brief notes), 'determine' (obtain a numerical value using given data or a method), and 'deduce' (reach a conclusion from information provided, not from outside knowledge). Each appears heavily in Paper 3 and internal assessment marking.

IB Biology mark schemes list acceptable points, each worth one mark, alongside guidance on alternative wording examiners will accept. For extended-response questions, markers also apply level-based descriptors (similar to a mini rubric) that reward structure, use of terminology, and linkage between ideas, not just isolated facts.

Error carried forward means if you make an early mistake in a calculation but apply correct method afterwards, you still earn the method marks for subsequent steps. It stops one arithmetic slip from costing every later mark, provided your working is shown clearly.

Usually because you answered the wrong command term, missed required terminology, or gave a correct fact without the linking reasoning the mark scheme demands. Correct biology alone doesn't guarantee marks — the mark scheme rewards the specific point made in the specific way the question's verb requires.

As a rule of thumb, match the number of distinct points in your answer to the marks available — a 3-mark 'outline' question usually needs three separate, distinct points, not one long paragraph repeating the same idea. Check the mark allocation in brackets before you start writing.

Paper 1 is multiple choice on core and (for HL) additional higher-level material. Paper 2 has short-answer and extended-response questions on the core and AHL syllabus. Paper 3 covers data-based questions plus your chosen option topic, with the option contributing roughly 20% of that paper's marks.

HL Biology uses the same command terms as SL, but questions push further up the demand ladder — more 'evaluate', 'analyse' and 'discuss' questions requiring synthesis across topics, and the additional AHL content adds density rather than new verb types. The command terms themselves don't change between levels.

Practise past paper questions grouped by command term rather than by topic, then check your answer against the official mark scheme line by line to see exactly which words earned marks. Repeating this across topics trains you to recognise what each verb actually demands under exam pressure.

The full glossary of command terms sits in the IB Biology guide, published by the International Baccalaureate for teachers and available through your child's school. Students don't need to buy anything extra — the definitions are consistent across all DP sciences, so learning them once covers Chemistry and Physics too.