# Explain how the fluid mosaic model accounts for the ability of membrane proteins to carry out their functions within the phospholipid bilayer.

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

## Mark scheme (4 marks)

1. Phospholipids are arranged in a bilayer with hydrophilic heads facing outward and hydrophobic tails facing inward, providing a stable but flexible framework
2. The 'fluid' nature of the bilayer arises because phospholipids can move laterally, allowing proteins to move within the membrane and adopt functional positions
3. Proteins are embedded ('mosaic') in the bilayer either spanning the full width (intrinsic/integral proteins) or attached to one surface (peripheral proteins), enabling diverse functions such as transport, signalling, or enzymatic activity
4. The specific tertiary structure / shape of each membrane protein is maintained within the bilayer, allowing precise interactions (e.g. with specific molecules / ligands / substrates) necessary for the protein's function

## Key terms

- [fluid mosaic model](https://www.gradenine.co.uk/glossary/fluid-mosaic-model)
- [phospholipid bilayer](https://www.gradenine.co.uk/glossary/phospholipid-bilayer)

## 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-fluid-mosaic-model-fa8b3d26) · Published by Druglandscape Ltd.