# Explain how enzymes lower the activation energy of a reaction, and outline why this is important for metabolic reactions in living cells.

> IB DP Biology Standard Level (2023 syllabus) — C1.1 Enzymes and metabolism · Explain · 4 marks

## Mark scheme (4 marks)

1. Enzymes bind substrate(s) at the active site to form an enzyme–substrate complex
2. Binding at the active site stresses/distorts bonds in the substrate (induced fit / transition state stabilisation), reducing the energy needed to reach the transition state
3. Lower activation energy means a greater proportion of substrate molecules have sufficient energy to react at a given temperature, so the reaction proceeds faster
4. This allows metabolic reactions to occur rapidly at the mild temperatures and near-neutral pH of living cells, which could not sustain the high temperatures otherwise needed to overcome activation energy barriers

## Key terms

- [activation energy](https://www.gradenine.co.uk/glossary/activation-energy)

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-enzymes-lower-the-activation-8bcdf311) · Published by Druglandscape Ltd.