# Explain why two organisms that can successfully interbreed and produce fertile offspring are classified as the same species, and describe two limitations of using this definition to classify all living organisms.

> AQA A-Level Biology (7402) — 3.4.5 Species and Taxonomy · Explain · 5 marks

## Mark scheme (5 marks)

1. Organisms that interbreed and produce fertile offspring share the same gene pool / can pass genes to the same next generation
2. Fertile offspring means the two parent organisms are sufficiently genetically compatible to be the same species
3. Limitation 1: the definition cannot be applied to organisms that reproduce asexually
4. Limitation 2: the definition cannot be applied to extinct / fossil organisms (cannot observe interbreeding)
5. Some organisms from different species can interbreed but produce infertile offspring (e.g. mules from horse and donkey), showing the definition has edge cases / is not always clear-cut

## Key terms

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

## Related

- [Revision notes for AQA A-Level Biology (7402)](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-why-two-organisms-that-can-b3463a0e) · Published by Druglandscape Ltd.