Microorganisms and food Edexcel International GCSE Science (Double Award) revision
Not started
Learn it
In plain words
Bread, yoghurt and many medicines are made by putting microbes to work. Yeast makes dough rise. Bacteria turn milk into yoghurt. On a factory scale, microbes are grown in huge steel tanks called fermenters, with everything kept exactly as they like it.
Three things to know
- Yeast respires anaerobically in bread dough, producing carbon dioxide, which makes the dough rise. The alcohol evaporates in the oven.
- Lactobacillus bacteria turn the lactose in milk into lactic acid. The acid makes the milk thicken into yoghurt and gives it its sharp taste.
- An industrial fermenter gives microorganisms ideal conditions: sterile (aseptic) so nothing else grows; nutrients; the best temperature and pH; oxygen if it's needed; and stirring to keep everything mixed.
Tips and tricks
- Each fermenter feature has a reason: the cooling jacket stops enzymes overheating, the paddles keep microbes in contact with nutrients, and steam sterilising prevents contamination.
- Bread rises because of carbon dioxide from yeast, not because of air.
It lands in your notebook with its questions as flashcards.
Microorganisms and food: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which gas makes bread rise?
Yeast gives it off as it respires.
Which bacteria are used to make yoghurt?
They make lactic acid from lactose.
What makes milk thicken into yoghurt?
The acid changes the milk proteins.
Why is a fermenter sterilised before use?
They would compete with the ones you want, or spoil the product.
Why does a fermenter have stirring paddles?
Stirring also spreads the heat and oxygen evenly.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 8 marks. Write your answers on paper, then check them.
Microorganisms and food
Edexcel International GCSE Science (Double Award) 4SD0 · 8 marks · papermunch.org
Name ______________________________ Date ______________
Explain why bread dough rises when yeast is added.[2]
Show answerHide answer
The yeast respires (anaerobically), producing carbon dioxide gas, which is trapped in the dough and makes it expand.
Describe how yoghurt is made from milk.[3]
Show answerHide answer
Lactobacillus bacteria are added to (pasteurised) milk and it is kept warm. The bacteria convert lactose to lactic acid. The acid lowers the pH, which makes the milk proteins thicken.
Give three conditions that are controlled in an industrial fermenter, and the reason for one of them.[3]
Show answerHide answer
Any three: temperature, pH, oxygen, nutrients, aseptic conditions, stirring. Reason, for example: temperature is controlled because the microorganisms' enzymes work best at an optimum temperature and are denatured if it is too high.
Answers: Microorganisms and food
- 1. The yeast respires (anaerobically), producing carbon dioxide gas, which is trapped in the dough and makes it expand.
- 2. Lactobacillus bacteria are added to (pasteurised) milk and it is kept warm. The bacteria convert lactose to lactic acid. The acid lowers the pH, which makes the milk proteins thicken.
- 3. Any three: temperature, pH, oxygen, nutrients, aseptic conditions, stirring. Reason, for example: temperature is controlled because the microorganisms' enzymes work best at an optimum temperature and are denatured if it is too high.