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Yeast

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A series of free Science Lessons for 7th Grade and 8th Grade, KS3 and Checkpoint Science in preparation for GCSE and IGCSE Science.

Fungi - Yeast
Yeast is an example of a single-celled fungus. They are useful in food production. The carbon dioxide produced by yeast makes bread dough rise, and the ethanol it produces makes beer and wine alcoholic.

How does yeast help the bread to rise?
What happens when we make bread? Hint: It involves plenty of yeast, trapping carbon dioxide and linking gluten molecules.



Yeast reproduction
Yeast cells reproduce asexually by producing a bud. This is a new cell that eventually breaks away from the parent cell.

The growth rate of a yeast population depends on:
1. the availability of food - such as sugar in wine-making.
2. the temperature - at low temperatures yeast are inactive and at high temperatures their enzymes are denatured.
3. the pH.
4. the removal of waste products - the ethanol yeast produce in wine-making eventually kills them.

Fermentation of Yeast in Sugar
In this experiment we are exploring the fermentation of yeast in sugar. Yeast uses sugar as energy and releases carbon dioxide and ethanol as waste. Yeast and fermentation have been used for thousands of years when making bread. At the end of this episode you will be able to demonstrate fermentation, explain why yeast and fermentation make a balloon grow and explain the chemical reaction that occurs during fermentation.
Yeast Experiment: measuring respiration in yeast
In the experiment, the respiration of yeast is tested in cold water, hot water and warm water.

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