# Explain how the concentration of cholesterol in the plasma membrane affects membrane fluidity and why this is important for normal cell function.

> IB DP Biology Higher Level (2023 syllabus) — B2.1 Membranes and membrane transport · Explain · 4 marks

## Mark scheme (4 marks)

1. Cholesterol molecules are interspersed among phospholipid tails in the bilayer
2. At high temperatures, cholesterol restricts phospholipid movement and reduces fluidity; at low temperatures, cholesterol prevents the membrane from solidifying / gelling by spacing phospholipids apart
3. Appropriate membrane fluidity is necessary for the lateral movement of membrane proteins such as receptor proteins, transport proteins, or enzymes
4. Correct fluidity also maintains selective permeability / integrity of the membrane, allowing normal vesicle formation, cell signalling, or cell recognition

## Key terms

- [cholesterol](https://www.gradenine.co.uk/glossary/cholesterol)
- [membrane fluidity](https://www.gradenine.co.uk/glossary/membrane-fluidity)

## 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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-concentration-of-cholesterol-a087a0db) · Published by Druglandscape Ltd.