Explain why the classification of organisms sometimes changes, and describe two types of evidence scientists use to determine whether organisms should be placed in the same group.

AQA A-Level Biology (7402) — 3.4.5 Species and Taxonomy · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

Classification changes when new evidence is found or scientific understanding improves.

Scientists use:
1. Molecular/genetic evidence – DNA or genome sequencing shows how closely related organisms are; those with more similar DNA are grouped together.
2. Physical/morphological evidence – observable body structures and features; organisms with similar morphology are placed in the same or closer groups.

Examiner tips

  • Use the word ‘classification changes’ to show understanding of why it happens. Mention both DNA/genetic and morphological evidence explicitly. Show the link between similarity and grouping.
  • Use concise, exam‑style language and avoid unnecessary words.

Common mistakes

  • Confusing ‘classification changes’ with ‘organisms change’. Forgetting to mention both types of evidence. Using vague terms like ‘similarity’ without specifying DNA or morphology.

Mark scheme (5 marks)

  1. Classification changes because new evidence becomes available / as scientific understanding develops
  2. Molecular / genetic evidence (e.g. DNA or genome sequencing) can reveal how closely related organisms are
  3. Organisms with more similar DNA / genes are placed in the same / closer groups
  4. Physical / morphological characteristics (e.g. body structure, observable features) are used as evidence
  5. Organisms with more similar physical characteristics are placed in the same group / closer together in the hierarchy

Key terms in this question

classification · evidence

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