# Explain how the structure of a gill lamella is adapted to facilitate efficient gas exchange in bony fish.

> IB DP Biology Standard Level (2023 syllabus) — B3.1 Gas exchange · Explain · 4 marks

## Mark scheme (4 marks)

1. Gill lamellae have a large surface area to increase the rate of diffusion of gases.
2. The epithelium of the lamella is very thin / one cell thick, reducing the diffusion distance for oxygen and carbon dioxide.
3. Lamellae have a rich capillary supply / dense network of blood capillaries bringing blood into close proximity with the water, maintaining a steep concentration gradient.
4. Blood flows through the lamellae in the opposite direction to the flow of water (countercurrent flow), maintaining a concentration gradient along the entire length of the lamella.

## Key terms

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

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-a-425154ee) · Published by Druglandscape Ltd.