# Explain why a molecule of ATP can release energy rapidly to drive cellular processes, whereas glucose cannot release its energy directly without first undergoing a series of enzyme-controlled reactions.

> OCR A-Level Biology A (H420) — 2.3 Nucleotides and nucleic acids · Explain · 4 marks

> Cells require a universal energy currency to couple energy-releasing reactions to energy-requiring ones. ATP fulfils this role in all living organisms, from bacteria to mammals.

## Mark scheme (4 marks)

1. ATP releases energy through hydrolysis of a phosphoanhydride bond, which is a single-step reaction
2. The energy released per hydrolysis of ATP is small and matched to the needs of cellular reactions, preventing wasteful heat loss
3. Glucose must first be broken down through a multi-step pathway (glycolysis / respiration) before its energy can be coupled to ATP synthesis
4. ATP acts as a universal / immediate energy currency, directly coupling to energy-requiring processes via phosphorylation

## Key terms

- [ATP](https://www.gradenine.co.uk/glossary/atp)
- [enzyme-controlled reactions](https://www.gradenine.co.uk/glossary/enzyme-controlled-reactions)

## 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/explain-why-a-molecule-of-atp-6e449c47) · Published by Druglandscape Ltd.