27 exam-style questions on Classification and cladistics — topic A3.2 of Unity and diversity in the IB Biology syllabus — with answers and explanations. Samples below; the full set is free with an account.
In a cladogram, what does a node (branching point) represent?
Answer: The most recent common ancestor of those taxa
Each node marks a hypothetical most recent common ancestor from which the descendant clades diverged.
Which term describes a group consisting of an ancestor and ALL of its descendants?
Answer: Monophyletic group (clade)
A monophyletic group, or clade, contains a common ancestor together with every one of its descendants.
Cladistics groups organisms using shared derived characteristics. What is the correct term for such a shared derived trait?
Answer: Synapomorphy
A synapomorphy is a derived character shared by taxa that inherited it from their most recent common ancestor; it defines a clade.
The wing of a bird and the wing of an insect perform the same function but evolved independently. In cladistic analysis these structures are best described as:
Answer: Analogous, from convergent evolution
Analogous structures arise by convergent evolution and, because they are not inherited from a common ancestor, they must not be used to build clades.
Why has molecular (base and amino acid sequence) data largely reinforced classifications, and sometimes led to reclassification of organisms?
Answer: Sequence differences reflect mutations since divergence
The number of differences between homologous sequences reflects time since divergence, giving an objective, quantitative basis for inferring relationships.
A parsimony analysis is used to choose between competing cladograms. Which cladogram is preferred?
Answer: The one requiring the fewest evolutionary changes
Parsimony favours the tree that explains the data with the smallest number of evolutionary changes, as this is the least assumption-heavy hypothesis.
That was 6 of 27 Classification and cladistics questions.
Practise all 27 freeStateAO1 · 1–2 marks
One word or one short sentence. No explanation, no working: the mark is for the fact itself.
OutlineAO2 · 1–4 marks
A brief account or summary: the main points in two or three sentences, no evaluation.
DistinguishAO2 · 1–4 marks
Make the difference clear for BOTH terms — a definition of one of them is only half an answer.
27 Classification and cladistics questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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