# A student wants to grow bacteria on agar plates to investigate the effect of temperature on the growth of microorganisms. Before the investigation begins, the student sterilises all equipment using an autoclave. Explain why each step in preparing and using the growth medium must be carried out under aseptic techniques, and describe what the growth medium must contain to allow successful culture of the bacteria.

> Pearson Edexcel A-Level Biology A (9BI0) — 5.1 Microbial growth and culture · Explain · 5 marks

> A student is preparing agar plates to culture bacteria at different temperatures. The student sterilises all equipment using an autoclave before beginning the investigation.

## Mark scheme (5 marks)

1. Aseptic techniques are used to prevent/minimise contamination of the culture
2. Contamination could introduce other microorganisms that would affect the results / make results unreliable
3. The autoclave sterilises equipment using high temperatures (to kill microorganisms / to destroy contaminating microorganisms)
4. The growth medium must contain carbohydrates (as an energy/carbon source) for bacterial growth
5. The growth medium must also contain proteins AND vitamins AND minerals (all three required for 1 mark)

## Key terms

- [aseptic techniques](https://www.gradenine.co.uk/glossary/aseptic-techniques)
- [autoclave](https://www.gradenine.co.uk/glossary/autoclave)
- [growth medium](https://www.gradenine.co.uk/glossary/growth-medium)
- [culture](https://www.gradenine.co.uk/glossary/culture)

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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-student-wants-to-grow-bacteria-805fd772) · Published by Druglandscape Ltd.