Knowing the biology is only part of answering an IGCSE Biology question. You also need to do what the command word asks. A detailed explanation can still miss a request to describe a graph, while a list of observations may not explain a mechanism. This guide focuses on describe, explain and compare, using examples rather than copied exam answers. Cambridge’s command-word guidance provides the foundation; your own syllabus and the mark scheme for a specific question remain the final references. Practise choosing the kind of answer before writing more facts.
Describe reports what happens, explain connects it to a biological reason, and compare relates the named subjects using matched features. Cambridge publishes guidance on these command words. Use the question’s context, data and mark allocation to decide the detail, then check that every sentence helps answer the actual task.
Biology marks reward more than recall
Use these assessment objectives to vary the questions in your revision.
Knowledge with understanding
Approximate qualification weighting for AO1.
Cambridge 0610 syllabus · 2026–2028 — original sourceInformation and problem-solving
Approximate AO2 weighting: includes interpreting unfamiliar data.
Cambridge 0610 syllabus · 2026–2028 — original sourceExperimental skills
AO3 covers investigations, including evaluating methods and results.
Cambridge 0610 syllabus · 2026–2028 — original sourceAfter revising a topic, answer a knowledge question, interpret a graph and evaluate an experimental method. For each, check whether your response actually follows its command word.
Context: Cambridge IGCSE Biology 0610, examinations 2026–2028. These are assessment-objective weightings, not the weights of individual papers or guaranteed marks for particular command words.
What do IGCSE Biology command words ask you to do?
Treat the command word as an instruction for your answer, not an optional clue. Cambridge’s guidance distinguishes describing characteristics, explaining reasons and comparing similarities or differences. The three examples in this guide practise those different tasks without claiming to reproduce an official marking scheme or predict the wording of your examination.
Underline the command word and the thing it refers to. “Describe the graph” and “describe the process” both use describe, but they require different content. Notice restrictions such as “using the data” or “between the two species.” A memorised paragraph can sound scientific while ignoring those boundaries.
| Command | Your job | Useful starting point |
|---|---|---|
| Describe | State the relevant pattern, features or events | As X increases, Y… |
| Explain | Give the biological reason or mechanism | This happens because… |
| Compare | Relate the named subjects on the same feature | Both… whereas… |
How do you describe a graph in IGCSE Biology?
Describe the pattern using the variables, direction and relevant values. In our invented seedling dataset, mean height rises from 2 cm on day 0 to 8 cm on day 6, then stays at 8 cm on day 9. That description reports the evidence without inventing a biological explanation for the plateau.
Include units when quoting values and distinguish a change from a constant interval. Avoid saying that the graph “goes up” without naming what increases. Also avoid turning an association into proof of a cause. If the question asks for a description, a speculative explanation uses space without completing the requested task.
data example, not an experimental result
- Weak: “It increases because plants photosynthesise.”
- More relevant: “Mean height increases from 2 cm to 8 cm between days 0 and 6.”
- Complete the pattern: “It remains at 8 cm from day 6 to day 9.”
- Do not claim why growth stopped: the dataset does not establish a cause.
| Day | Mean seedling height |
|---|---|
| 0 | 2 cm |
| 3 | 5 cm |
| 6 | 8 cm |
| 9 | 8 cm |
How do you turn a fact into an explanation?
Connect the observation to the process that causes it. In this diffusion example, oxygen moves into a cell when its concentration is higher outside than inside. A useful explanation identifies the concentration gradient and net movement down that gradient, rather than repeating that the cell “needs oxygen” as the whole answer.
Build a chain in which each sentence supports the next. Keep it relevant to the question’s assumptions. You do not need to include every fact you know about respiration, membranes and blood. If a term such as diffusion is central, use it accurately and connect it to the substances and direction in the example.
prompt: explain net oxygen movement into a cell
- Given: the oxygen concentration is higher outside the cell than inside.
- State the process: oxygen molecules cross by diffusion.
- Connect the direction: net movement is down the concentration gradient, from outside to inside.
- Check the explanation: it names the substance, the process and the reason for the direction.
- Avoid “oxygen chooses to enter” or other language suggesting molecules act deliberately.
What makes a comparison clear?
Compare the same feature across both subjects. In our red-blood-cell comparison, both a mature human red blood cell and a typical plant leaf cell have a cell membrane, while the plant cell has a cellulose cell wall and the mature human red blood cell does not. Naming both sides prevents an incomplete contrast.
Be precise about the objects in the question. Not every plant cell has chloroplasts, and “animal cell” is broader than a mature human red blood cell. Avoid absolute statements that are only true for a specific example. A compact table can help you plan, but write in the format requested by the question.
| Feature | Typical photosynthetic leaf cell | Mature human red blood cell |
|---|---|---|
| Cell membrane | Present | Present |
| Cellulose cell wall | Present | Absent |
| Nucleus | Present | Absent |
| Chloroplasts | Present in a typical photosynthetic leaf cell | Absent |
How much should you write?
Use the mark allocation to judge scope, but do not treat a mark as an automatic sentence count. An answer can contain several relevant points in one sentence or repeat the same point across several sentences. The exact question and its official mark scheme determine what earns credit, not a universal paragraph formula.
Draft direct points first, then check for missing links or unsupported statements. In an explanation, the relationship between points often matters as much as naming a term. In a comparison, make the pairing explicit. If you run out of space, look for repeated introductions and background material that the question never requested.
- Name the variable, organism or structure accurately.
- Use values and units when the question calls for data.
- Connect causes to effects in an explanation.
- Match features across both subjects in a comparison.
- Remove facts that do not answer the instruction.
A revision routine for Biology command words
Practise changing the task while keeping the topic familiar. Use the seedling data to describe a pattern, then separately list information you would need before explaining it. This contrast makes the boundary between evidence and explanation visible. It also prevents revision from becoming a search for one memorised paragraph per chapter.
Keep a small log of answers that missed the instruction. Record the command, what you wrote and what was missing. Ask a teacher to check borderline cases against your syllabus. A tutor can help you revise the answer while preserving your own reasoning, rather than supplying a script to memorise.
self-check routine
- Choose one question and underline its command and subject.
- Write an answer without notes.
- Highlight observations in one colour and reasons in another.
- Check whether the mix matches the command.
- Rewrite only the missing or irrelevant part; then try a fresh question.
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A few more answers.
Does “describe” mean I should never use because?
Focus on the task rather than banning a word. A graph description usually needs an accurate pattern and supporting data. If you add a reason, make sure it is requested and supported. The specific question and mark scheme matter more than a blanket rule about wording.
Can I answer Biology questions in bullet points?
Clear bullet points can organise an answer when the question permits them, but they must still express complete scientific ideas. An explanation needs logical connections, and a comparison needs matched features. Follow any instruction asking for continuous writing, a table, labels or a calculation.
Should I memorise mark schemes?
Use them to understand the expected precision and to check a specific answer. Memorising isolated phrases can fail when the context changes. Learn the biology behind the point, then practise expressing it accurately in a new question without copying the wording.
Does this guide apply to every exam board?
The general distinction is useful, but this article references Cambridge guidance. Confirm the command words, syllabus and assessment expectations for your own board. Do not assume a Cambridge example is a complete model answer for a Pearson or school examination.
Sources & further reading
Explore the original resources for more detail. Practice examples in this guide are illustrative, not official examination questions.
Cambridge International: understanding command wordsCambridge International: Biology 0610 syllabusYour questions. The right teacher.
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