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To compare the growth of yeast between two yeast suspensions.

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Yeast Growth under the Microscope

Aim: To compare the growth of yeast between two yeast suspensions


  • 2 Sterile conical flasks                        
  • Non-absorbent cottonwool plugs                
  • 50 mL of grape juice                                
  • 1 teaspoon of sugar                                
  • dry active yeast, half a packet
  • Bunsen burner
...read more.


  • gauze mat
  • Microscope
  • 2 Glass slides
  • 2 glass cover slips
  • 2 dropping pipettes


25mL of grape juice, and half a teaspoon of sugar was added to Flask A, then heated to boiling point for one minute. A thermometer was then placed in the flask and plugged with cottonwool. Flask A was then left to cool down to 30°C. Once the flask reached 30°C the cottonwool was quickly taken out and a quarter of a packet of yeast was added, as quickly as possible the cottonwool plug was replaced.

The rest of the grape juice and sugar was then placed in Flask B and then heated at boiling for one minute.

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°C and therefore sterilised or killed. The purpose of boiling the grape juice and sugar is to fully dissolve the sugar so that it provides food for the yeast to live off. It is important to start with sterile flasks because otherwise there is a risk of contamination and possibly brewing pathogens. It is important to replace the cotton wool immediately after the addition of yeast because otherwise airborne contaminants may enter the flask and ruin the experiment. While adding the yeast it was important not to put the cotton wool on the bench because the cottonwool may get contaminated. The yeast was activated by providing the right environment for example the necessary nutrients and temperature.

...read more.

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