# Explain how the concept of a species is used to define the boundary between two closely related organisms, and outline one limitation of applying this concept in practice.

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

## Mark scheme (4 marks)

1. A species is defined as a group of organisms that can interbreed / mate with one another
2. to produce fertile / viable offspring
3. Two organisms belong to different species if they cannot interbreed to produce fertile offspring / there is reproductive isolation between them
4. One limitation: the biological species concept cannot be applied to asexually reproducing organisms / fossils / bacteria, OR ring species / hybridising species complicate the boundary

## Key terms

- [species](https://www.gradenine.co.uk/glossary/species)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-concept-of-a-8d8888d6) · Published by Druglandscape Ltd.