Investigate one factor that affects the rate of respiration of yeast

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Isaac Wong 11H                 Biology

Biology Coursework

Investigate one factor that affects the rate of respiration of yeast

Plan

Aim:

In my experiment, my aim is to find out any correlation between the rate of respiration of yeast and the concentration of glucose in the yeast. I shall do this by conducing an experiment which will involves a steady increment of glucose and for each increment, I will measure the temperature to see whether if it increases and the rate of increment.

There are many factors (variables) that could affect this investigation such as the temperature the yeast respires at as at different temperatures the enzymes in yeast work faster or slower at breaking down the glucose. The amount of yeast will also have an effect on the results, if we are to use different amounts in each experiment it will form an unfair test. I must also make sure to leave all experiment undisturbed during the course of respiring, this means they cannot be stirred or let air get to them.

I have chosen to investigate the affect the % concentration of glucose has on rate of respiration in yeast. I will use an experiment to determine whether the yeast’s rate of respiration will increase, decrease or if it will stay constant even when the % concentration of glucose in it is varied.

Prediction:

I predict that the yeast’s respiration rate of reaction should increase in speed as the % of glucose increases. However this may at some point peak and therefore cease to increase in speed.

Fermentation is an anaerobic process and which turns glucose into ethanol and carbon dioxide. In this experiment the yeast will be carrying out respiring anaerobically and breaking down the glucose and giving ethanol and carbon dioxide as waste products. There are enzymes in the yeast to break the glucose down.

My reason for my prediction is that the more glucose that is present in the yeast the more will be broken down and therefore more carbon dioxide and ethanol will be produced and at a faster rate. The rate should be faster because as the % of glucose increases, the chance for the enzymes (in yeast) coming into contact with glucose molecules will be higher, therefore increases the rate of fermentation. If the concentration is low, the number of glucose molecules will be less and therefore the rate of fermentation decreases.

The conversion of glucose to carbon dioxide and ethanol takes place in the active site of the enzyme. Enzymes are protein chains of amino acids. Their molecules are very precise three-dimensional shapes.

The shape includes a 'dent', which is exactly the right size and shape for a molecule of the enzyme's substrate (in this case glucose) to fit into. This 'dent' is called the active site. When the glucose molecule slots into the active site, the enzyme changes it, pulling it out of shape and making it split into product molecules. The product molecules (in this case carbon dioxide and ethanol) then leave the active site, which is now ready to do the same to another glucose molecule. So if there are many glucose molecules (10% concentration) there will be more chance that these molecules can enter the active site and produce a fast rate of fermentation.

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The predicted outcome (graph)

Factors that can affect the outcome:

Temperature: (a factor I am going to keep constant)

The temperature will have a great affect on the results because according to the kinetic theory, the higher the temperature the reaction takes place in, the higher the rate of reaction is. However, in this experiment the process of fermentation depends on enzymes. All enzymes have a certain temperature they work fastest at (also known as optimum temperature). If the temperature exceeds the optimum temperature, enzymes starts to ...

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