# A student is investigating the effect of salt concentration on the mass of potato cylinders using osmosis. Describe how the student should design a reliable investigation, including how variables should be controlled.

> OCR GCSE Biology A: Gateway Science (J247) — B7 Practical skills · Describe · 4 marks

> A student wants to find out whether increasing the concentration of salt solution causes potato cylinders to lose mass. They have access to potato, salt solution at a range of concentrations, distilled water, a balance, and standard laboratory equipment.

## Mark scheme (4 marks)

1. Identify the independent variable as the concentration of salt solution
2. Identify the dependent variable as the change in mass of the potato cylinders
3. State at least one controlled variable with a reason
4. State that repeats should be carried out at each concentration to improve reliability

## Key terms

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

## Related

- [Revision notes for OCR GCSE Biology A: Gateway Science (J247)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-is-investigating-the-effect-2b850ac0) · Published by Druglandscape Ltd.