# 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.

> IB DP Biology Higher Level (2023 syllabus) — A3.1 Diversity of organisms · Explain · 4 marks

## Mark scheme (4 marks)

1. Biological species concept defines a species as a group of organisms that can interbreed and produce fertile/viable offspring
2. Morphological species concept defines a species based on shared physical/structural characteristics or appearance
3. Limitation of the biological species concept: cannot be applied to asexually reproducing organisms / fossils / bacteria, since interbreeding is absent or untestable
4. 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

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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