Biology Planning Exercise.

The blue indicator will go colourless in the presence of active enzymes, therefore indicating living cells are present and are respiring.

Reagents:10% suspension of yeast – in the instructions we were told we could use either dried/fresh baker’s yeast. I will use fresh baker’s yeast due to possible problems with dried baker’s yeast e.g.

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clumping into grains so harder to count due to dehydration.

c. Prepare water bath at 20, 40, 60 and 80°C (Independent variables). It’s better to raise the temperature of the water baths gradually as a rapid increase can overwhelm the enzymes and denature them, meaning unreliable results.

a. Take 1ml of the yeast solution from each test tube. Transfer the sample to ice bath. The purpose is to reduce the metabolism and reproduction of the yeast but keep them alive. Drop 1 ml of methylene blue respectively and wait for 30 seconds. (Do the same to the control and identify the existence of yeast in the glucose solution.)

All of the above procedures were used in my preliminary and the difficulty I found was in counting the yeast cells as accurately as possible with using the microscope. I later discovered another piece of equipment could have been used to measure the total number of cells, called a haemocytometer. I obtained the following results:

What the trend shows is that as temperature increases the % of Yeast cells that remain active decrease. Therefore we say the two values are inversely proportional. From the point the temperature reaches 40°C there is a rapid drop in Yeast viability as the enzymes become denatured and the high temperatures interefere with the shapes of the active sites. So what I can conclude is that the tempertature of interest for the main investigation is between 40ºC to 50ºC. Therefore for the main experiment I can can separate the temperature into groups: 40-42, 42-44, 44-46, 46-48, 48-50.

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