# A yeast culture is kept in a sealed container with a limited supply of glucose and no oxygen. Explain what happens to the rate of cellular respiration in the yeast cells over time as the glucose is used up, and describe how the products of respiration differ from those produced when oxygen is available.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 4.1 Cellular respiration · Explain · 5 marks

> Yeast can respire both aerobically and anaerobically depending on the availability of oxygen and glucose.

## Mark scheme (5 marks)

1. Without oxygen, yeast respires anaerobically
2. Anaerobic respiration in yeast produces ethanol (alcohol) and carbon dioxide
3. When oxygen is available, aerobic respiration produces carbon dioxide and water (not ethanol)
4. As glucose is used up, the rate of respiration decreases / slows down
5. Glucose is the reactant / substrate for respiration, so as it is depleted there is less substrate available for respiration to occur

## Key terms

- [glucose](https://www.gradenine.co.uk/glossary/glucose)
- [cellular respiration](https://www.gradenine.co.uk/glossary/cellular-respiration)

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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-yeast-culture-is-kept-in-9dc91ced) · Published by Druglandscape Ltd.