# A student wants to grow bacteria on an agar plate to investigate the effect of temperature on bacterial growth. Explain why the student must use aseptic techniques throughout the procedure and describe two specific aseptic techniques the student should use when preparing the culture.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 5.1 Microbial growth and culture · Explain · 5 marks

> The student uses an autoclave to sterilise equipment before beginning the investigation.

## Mark scheme (5 marks)

1. Aseptic techniques are needed to prevent contamination of the culture by unwanted microorganisms
2. Contamination would mean results are unreliable / invalid because the bacteria present would not be the intended species
3. Specific aseptic technique 1: flaming / passing the inoculating loop through a Bunsen burner flame to sterilise it before and after use
4. Specific aseptic technique 2: briefly passing / flaming the neck of the culture bottle/flask when it is opened to prevent airborne contamination entering
5. The lid of the agar plate should be replaced quickly / taped down / not left open to minimise the time the culture is exposed to the air

## Key terms

- [aseptic techniques](https://www.gradenine.co.uk/glossary/aseptic-techniques)
- [culture](https://www.gradenine.co.uk/glossary/culture)
- [agar plate](https://www.gradenine.co.uk/glossary/agar-plate)

## 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-student-wants-to-grow-bacteria-dda1f1dd) · Published by Druglandscape Ltd.