Investigating Anaerobic Respiration in Yeast

I will carry out an investigation into one of the following factors to see how it effects the amount of anaerobic respiration that the yeast performs.

Factors affecting rate of respiration:

* Concentration of glucose solution

* Temperature that fermentation is carried out under

* Quantity of yeast

Concentration of Glucose solution - this will not speed up the

Temperature that fermentation is carried out under - yeast breaks the glucose down using enzymes and enzymes work most efficiently at certain temperatures. I could investigate into what the most effective temperature is.

Quantity of yeast - the more yeast the more enzymes to break down the glucose but

Chosen Factor

I have chosen to investigate how the temperature effects the rate of respiration of yeast. I chose to investigate this because I think it will generate some clear and meaningful results that can be re-tested easily.

Method

To measure the rate that the yeast breaks down the glucose I could measure the amount of carbon dioxide released per minute. The more carbon dioxide released per minute the more glucose that is being broken down and the more alcohol released, So the quicker the fermentation. The yeast would be working most efficiently when there is the most amount of carbon dioxide released per minute.

The amount of carbon dioxide released could be measured as shown below:

The yeast is put in the test tube with the glucose solution and a timer started. The measuring cylinder is filled with water and as CO2 is released in the test tube by the break down of the glucose the air pressure increases pushing more water out of the measuring cylinder. The experiment will probably last for10 minutes but a more suitable time span can be determined after the preliminary test. By measuring the amount of CO2 every minute I can plot an accurate graph of the rate of respiration of the yeast. This would make it very easy to compere the effect that the different temperatures.

To make it a fair test and to make sure I am only investigating the effect that the temperature has on the rate that the yeast respires I must keep all the other factors the same. I must always use the same amount of yeast and glucose, I must always start the clock as soon as the yeast and the glucose come into contact and put the bung on straight away. The glucose solution will always be pre heated to the right temperature before the yeast is added because then the glucose doesn't have to adjust to the right temperature.

I will run the experiment at 5 different temperatures to gather a range of different results. I will repeat the experiment at each temperature 3 times so I can get an average set of results for each temperature which will minimise any accidental errors. The book 'Essential Science' says that the enzyme that breaks down glucose in yeast works best at 37oc and recommends using water baths between 0oc and 400c so my five temperatures will be 200c 300c 370c 400c 450c. This should then generate this sort of graph:

Most carbon dioxide will be released when the glucose solution is 370c but ether side of this temperature less glucose will be released. When the temperature differs too much from 370c the enzymes will not function that is why I made the graph start off gradual.