1. Microbiology
Photo: Matt Meadows, Peter Arnold Inc.

2. What do microbes need to grow?
Food.
Often – but not always – oxygen.
Warmth.
If bacteria have everything they need they grow and divide very fast indeed.
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3. How do you grow bacteria in the lab?
Microorganisms are grown on nutrient agar.
The agar is heated to around 120°C to kill off any unwanted microbes already present.
Then a number of steps are followed ...
Photo: Digital Stock 7 (NT)
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4. 1 Sterilise the inoculating loop, used to transfer microorganisms to the agar, by heating it to red-hot in the flame of a Bunsen and then leaving it to cool.
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5. 2 Dip the sterilised loop in a suspension of bacteria.
3 Use it to make zig-zag streaks across the surface of the agar.
4 Tilt the lid on your Petri dish to keep out unwanted microbes and close the lid quickly to avoid contamination.
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6. 6 Incubate the culture at no more than 25°C for several days.
5 Secure the lid of your Petri dish with short pieces of tape to prevent microorganisms from the air contaminating your culture – or microbes from your culture escaping. Do not seal all the way around the edge.
6 Incubate the culture at no more than 25°C for several days.
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7. How does yeast help us to make bread?
Aerobic respiration in yeast (with oxygen) produces carbon dioxide and water.
Carbon dioxide makes the bread rise.
Photos: Stewart Miller
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8. What part does yeast play in making alcoholic drinks?
When yeast respire anaerobically (without oxygen), they break down sugar to produce carbon dioxide and ethanol.
In beer-making – yeast is added to sugar from germinating barley.
In wine-making – natural yeast on grapes acts on the sugars in the grape juice.
Photo: Ringwood Brewery
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9. How are bacteria used to make food?
Yoghurt – bacteria undergo lactic fermentation. They break down lactose, (milk sugar) to produce lactic acid. This clots the milk and thickens the yoghurt.
Cheese – different bacteria, same lactic fermentation as in yoghurt-making, but much more lactic acid, produces the solid curds used to make cheese.
Photo: Photodisc 67 (NT)
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10. How do we culture microbes on a large scale?
Photo: SPL Maximillian Stock
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11. How do microbes kill microbes?
The fungus Penicillium makes a chemical that kills bacteria.
The chemical can be extracted and purified to make penicillin, a medicine that is safe for people to use and cures many bacterial diseases.
Penicillin is produced in large fermenters.
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12. What is biogas? Mainly methane.
Produced when bacteria break down animal waste products or plant material in anaerobic conditions.
Biogas generators are used around the world to produce cheap fuel.
Different types of generators are needed for different conditions.
Photo: SPL David Hall
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13. How can microbes make fuel for your car?
When yeast respire anaerobically, they produce ethanol.
Ethanol can be used as a fuel for cars, either pure or mixed with petrol.
The action of yeast on sugar cane or sugar from maize produces ethanol for cars.
The main problem is growing enough plants to produce the ethanol.
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