# Explain how the concept of reproductive isolation is central to the biological species concept.

> IB DP Biology Standard Level (2023 syllabus) — A4.1 Evolution and speciation · Explain · 4 marks

> The biological species concept defines a species as a group of organisms that can interbreed and produce fertile offspring, but are reproductively isolated from other such groups.

## Mark scheme (4 marks)

1. Reproductive isolation prevents gene flow between populations / prevents interbreeding between different species
2. Without gene flow, isolated populations accumulate different alleles / genetic differences over time through independent mutation, genetic drift, or natural selection
3. Members of the same species share a common gene pool / can interbreed to produce fertile offspring, which defines their unity as a species
4. Once reproductive isolation is complete / absolute, the two populations are considered separate species because interbreeding is no longer possible even if they come into contact

## Key terms

- [reproductive isolation](https://www.gradenine.co.uk/glossary/reproductive-isolation)
- [biological species concept](https://www.gradenine.co.uk/glossary/biological-species-concept)

## 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-reproductive-221fa979) · Published by Druglandscape Ltd.