# A student is culturing bacteria on agar plates in a school laboratory. Describe the aseptic techniques the student should use when preparing and incubating the agar plates to minimise contamination.

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

> A student wants to grow a pure culture of a known bacterium. They inoculate an agar plate with the bacterium and leave it to incubate. They must follow strict aseptic techniques throughout the procedure.

## Mark scheme (5 marks)

1. Sterilise the inoculating loop (e.g. by passing it through a flame) before and after use
2. Sterilise the agar plate / equipment using an autoclave before use
3. Work near a Bunsen burner flame to create an upward air current that reduces the settling of airborne microorganisms
4. Seal the lid of the agar plate with adhesive tape / Parafilm after inoculation to prevent contamination
5. Incubate the plates upside down at no more than 25 °C (in a school laboratory) to prevent condensation dripping onto colonies and to limit growth of human pathogens

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-is-culturing-bacteria-on-4f7411b4) · Published by Druglandscape Ltd.