# Explain the biological advantages of internal fertilisation over external fertilisation in animals.

> IB DP Biology Higher Level (2023 syllabus) — D3.1 Reproduction · Explain · 4 marks

## Mark scheme (4 marks)

1. Internal fertilisation occurs within the body of the female, protecting gametes from desiccation / drying out in a terrestrial environment.
2. Fewer gametes (especially sperm) need to be produced because the probability of a sperm meeting an egg is much higher than in an aquatic / open environment, reducing the energetic cost to the organism.
3. The fertilised egg / zygote / embryo can be retained within the female body (or protected by a shell / egg case), providing physical protection against predation and environmental hazards.
4. Internal fertilisation is essential for colonisation of terrestrial habitats because water is not required as a medium for sperm to swim to the egg.

## Key terms

- [internal fertilisation](https://www.gradenine.co.uk/glossary/internal-fertilisation)
- [external fertilisation](https://www.gradenine.co.uk/glossary/external-fertilisation)

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-the-biological-advantages-of-internal-6dbb0d43) · Published by Druglandscape Ltd.