# Explain how vesicle fusion during exocytosis results in the secretion of proteins from a cell and describe one consequence of this process for the plasma membrane.

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

## Mark scheme (4 marks)

1. Secretory vesicles (containing proteins) move towards and fuse with the plasma membrane
2. The vesicle membrane merges with the plasma membrane, opening the vesicle lumen to the extracellular space, releasing the protein contents
3. The phospholipid bilayer of the vesicle membrane is added to the plasma membrane, increasing its surface area
4. Membrane proteins originally in the vesicle membrane become inserted into the plasma membrane, potentially altering its composition or function

## Key terms

- [exocytosis](https://www.gradenine.co.uk/glossary/exocytosis)
- [vesicle fusion](https://www.gradenine.co.uk/glossary/vesicle-fusion)
- [plasma membrane](https://www.gradenine.co.uk/glossary/plasma-membrane)

## 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-vesicle-fusion-during-exocytosis-e4687420) · Published by Druglandscape Ltd.