Explain how the concept of a biological species differs from that of a morphological species, and outline one limitation of each concept when applied to living organisms.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The biological species concept defines a species as a group of organisms that can interbreed and produce fertile, viable offspring.
The morphological species concept defines a species on the basis of shared physical or structural characteristics, i.e. appearance.
A limitation of the biological species concept is that it cannot be applied to asexually reproducing organisms, fossils or many bacteria, because inter‑breeding is absent or untestable.
A limitation of the morphological species concept is that cryptic species – organisms that look identical but are reproductively isolated – would be incorrectly grouped as a single species, and the choice of which traits to use is subjective.
The morphological species concept defines a species on the basis of shared physical or structural characteristics, i.e. appearance.
A limitation of the biological species concept is that it cannot be applied to asexually reproducing organisms, fossils or many bacteria, because inter‑breeding is absent or untestable.
A limitation of the morphological species concept is that cryptic species – organisms that look identical but are reproductively isolated – would be incorrectly grouped as a single species, and the choice of which traits to use is subjective.
Examiner tips
- Use the exact terminology (biological species concept, morphological species concept).
- Show the two limitations clearly, one for each concept.
- Keep the answer concise – 4 marks, no extra words.
Common mistakes
- Confusing the two concepts or using the wrong definition.
- Failing to mention a specific limitation for each concept.
Mark scheme (4 marks)
- Biological species concept defines a species as a group of organisms that can interbreed and produce fertile/viable offspring
- Morphological species concept defines a species based on shared physical/structural characteristics or appearance
- Limitation of the biological species concept: cannot be applied to asexually reproducing organisms / fossils / bacteria, since interbreeding is absent or untestable
- Limitation of the morphological species concept: cryptic species (organisms that look identical but are reproductively isolated) would be incorrectly grouped as one species / subjective judgement of which features to use
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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