Culturing Microorganisms (Required Practical)

This lesson covers the techniques used to culture microorganisms safely, as required by the AQA GCSE Combined Science Trilogy specification (8464). This is a Required Practical — you need to know the method, understand aseptic technique and be able to calculate the areas of bacterial colonies and zones of inhibition.

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Why Culture Microorganisms?

Scientists grow (culture) microorganisms for several important reasons:

• To investigate the effect of antibiotics or antiseptics on bacterial growth.
• To study bacterial reproduction and growth rates.
• To produce useful substances (e.g. antibiotics, enzymes, insulin using genetically modified bacteria).

In schools, bacteria are grown on agar plates (Petri dishes containing a nutrient jelly) at controlled temperatures.

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What Bacteria Need to Grow

To grow and reproduce, bacteria need:

Requirement	Provided By
Nutrients (carbon source, nitrogen source, minerals)	Nutrient agar or nutrient broth
Warmth	An incubator set to a specific temperature
Moisture	Provided by the agar jelly
Time	Bacteria reproduce rapidly — populations can double every 20 minutes

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Aseptic Technique