# A student is investigating how the volume of carbon dioxide gas produced changes over time when yeast is mixed with glucose solution. The student collects the gas using an upturned measuring cylinder filled with water. Explain how the student should carry out a fair and accurate investigation, including how they should control variables and record results reliably.

> OCR A-Level Chemistry A (H432) — 1.1 Practical skills assessed · Explain · 5 marks

> Yeast breaks down glucose in a process that releases carbon dioxide gas. A student wants to find out how the volume of carbon dioxide collected changes over the first ten minutes of the reaction.

## Mark scheme (5 marks)

1. Measure and record the volume of gas collected at regular, equal time intervals (e.g. every minute)
2. Keep one variable constant / controlled, e.g. temperature, volume of glucose solution, concentration of glucose, or mass of yeast
3. Change only one independent variable at a time (e.g. temperature or concentration of glucose) to make the test fair
4. Repeat the experiment (at least three times) and calculate a mean volume to improve reliability / reduce the effect of anomalous results
5. Ensure the measuring cylinder is fully filled with water at the start and that the gas is collected without leaks, so measurements are accurate

## Related

- [Revision notes for OCR A-Level Chemistry A (H432)](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/a-student-is-investigating-how-the-df474ad0) · Published by Druglandscape Ltd.