Cells obtain energy through a process called respiration. Yeast normally respires aerobically. In the absence of oxygen, yeast carries out anaerobic respiration. Yeast carries out alcohol fermentation which is catalysed by the enzyme zymase to produces ethanol, carbon dioxide and energy. Ethanol is used in making wine.
Alcohol fermentation equation:
Glucose Alcohol + Carbon dioxide
C5H12O5 2C2H5OH + 2CO2
The rate of fermentation is influenced by several factors like temperature, type of sugar solution, concentration of yeast and concentration of glucose. In order to measure the rate of fermentation, the rate of production of carbon dioxide is measured in this experiment.
Aim:
To investigate how volume of yeast suspension may influence the rate of fermentation.
Hypothesis:
As the volume of yeast suspension increases, the rate of fermentation also increases.
Variables:
Independent variable : Volume of yeast suspension
Dependent variable : Rate of fermentation
Constant variable : Concentration of glucose, type of sugar solution, temperature, time taken for the rate of fermentation.
Materials & Apparatus:
50-mL of measuring cylinder, 2-ml of graduated pipette, yeast suspension, glucose solution, 37oC warm water, burette, stopwatch, test tube, delivery tube, and basin.
Methods:
1) 20mL of glucose solution was added to the test tubes using a 50mL measuring cylinder.
2) 2mL of yeast suspension was added to the solution in test tubes using a 2mL graduated pipette.
3) The end of the test tubes were covered with the thumb and the test tubes were inverted several times to thoroughly mix the contents of the test tubes.
4) The test tubes were covered with a stopper.
5) The delivery tube was attached, measuring cylinder was filled with water and the apparatus was set up so that gas produced will be collected in the measuring cylinder. Two sets of apparatus were set up where one of them acts as a control.
6) The test tubes were placed in a beaker which is ¾ full with warm water at 370C to ensure a suitable environment.
7) The volume of gas produced in the measuring cylinder was observed and recorded every 5 minutes for a total of 40 minutes.
8) The experiment was repeated by using 4mL of yeast suspension instead of 2mL of yeast suspension.
9) A table was constructed to record the time of measurements and the total volume of carbon dioxide produced for both experiment. A graph was constructed.
Discussion:
Based on the graph, the curve for experiment which uses 4ml of yeast suspension is steeper than the curve for experiment which uses 2ml of yeast suspension. We can conclude that as the volume of yeast suspension increases, the volume of carbon dioxide produced also increases. When more volume yeast suspension is used the reactant will increase causes the frequency of collision to be increase too. So, higher productive collision will happen and causes the product which is carbon dioxide to be released will increase. The results can be said precise as the readings are close to each other in both experiments. However, the reading for the experiment which uses 4ml of yeast suspension at minute of 35 and 40 is not precise as it has quite big difference. The graph has no scattered points and this indicates that random errors are not very significant for this experiment. Random error such as the temperature of the water bath is not consistent to 37°C and this may affect the result obtained. Besides that, another possible random error is the inability of human to react fast when using stopwatch. He might start take time or end the time slowly or quickly. So, it may affect the precision of the results. Improvements can be done by using an incubator as its water bath which its temperature will not drop or gain once it is fixed to 37°C. The person with stopwatch must really quick to start the stopwatch exactly after the delivery tube is connected to the test tube containing yeast suspension and glucose solution. The accuracy cannot be commented as the true value is not given in both experiments. However, based on the theory it is true that when the volume of yeast suspension increases, the volume of carbon dioxide produced also increases. Systematic errors such as the burette might not be calibrated properly. Some of the carbon dioxide gas might dissolve in water and affects the actual volume of carbon dioxide gas produced. Therefore, improvements such as use only the burette which is perfectly calibrated and gas syringe is used to collect the exact amount of carbon dioxide produced. It is important to use a lot of samples because a more reliable result can be obtained and the effect of random errors will be reduced. So, the results obtained can be more precise. Repeating the experiment also is important as it will increase the validity of results.
Conclusion:
As the volume of yeast suspension increases, the rate of fermentation also increases. Hypothesis is accepted.