# A student investigates the effect of a competitive inhibitor on the rate of an enzyme-controlled reaction. The student finds that increasing the substrate concentration eventually restores the original maximum rate of reaction. Explain why increasing substrate concentration overcomes competitive inhibition.

> OCR A-Level Biology A (H420) — 2.4 Enzymes · Explain · 4 marks

## Mark scheme (4 marks)

1. Competitive inhibitor has a similar shape to the substrate and binds to the active site
2. Inhibitor binding is reversible / temporary
3. At higher substrate concentrations, substrate molecules outcompete the inhibitor for the active site
4. At very high substrate concentrations, virtually all active sites are occupied by substrate, so Vmax is restored

## Key terms

- [competitive inhibitor](https://www.gradenine.co.uk/glossary/competitive-inhibitor)
- [substrate concentration](https://www.gradenine.co.uk/glossary/substrate-concentration)
- [maximum rate of reaction](https://www.gradenine.co.uk/glossary/maximum-rate-of-reaction)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](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/a-student-investigates-the-effect-of-578e16a8) · Published by Druglandscape Ltd.