Aim: The aim of this experiment is to compare the rate of reactions of the reaction of yeast with the three different carbohydrates, namely glucose, sucrose, and lactose.
Hypothesis: The rate of reaction should be fastest in the reaction between yeast and sucrose, since sucrose is broken down to two molecules of glucose, thereby giving more glucose for the yeast to act on. Therefore, for the same amount of glucose and sucrose, there will ultimately be double the amount of glucose in sucrose because the yeast will break down the sucrose into two times the amount of glucose.
Theory: The three carbohydrates being used in this experiment fall into two categories; monosaccharide and disaccharide. Glucose is a monosaccharide, whereas sucrose and lactose are disaccharides. One sucrose molecule breaks down to give two molecules of glucose, and a molecule of lactose breaks down to give a molecule of glucose and a molecule of galactose.
Yeast is a microbiologist that is used for fermentation. It respires anaerobically to produce carbon dioxide gas and alcohol. The yeast used in this experiment will be able to digest the sucrose, but the lactose in a disaccharide that is digested only by the enzyme lactase. Hence, we can expect no bubbles of carbon dioxide to be released for the reaction with lactose.
Yeast + Glucose ==> Ethanol + Carbon dioxide
C6H12O6 ==> 2C2H5OH + 2CO2
Planning: To carry out this experiment, I have to measure the
Data Collection: The data that had to be collected for this experiment was the number of carbon dioxide bubbles released in the reaction in five minutes’ time. The rate of there action with different carbohydrates can then be measured and compared.
Data Processing and Presentation:
From the graph above, it can be observed that the lactose is not digested by yeast and thus no reaction occurs in that test-tube. Within the other two carbohydrates, sucrose shows a faster rate of reaction, as we had hypothesized.
Conclusion: The conclusion drawn from this experiment is that the rate of reaction of fermentation with yeast is fastest with the sugar sucrose, whereas lactose is not even digested by the yeast.
Limitations and modifications: This experiment had a very big limitation. It was as follows:
* The temperature being measured was of the water bath in which the test-tubes containing the sugar solutions were kept. It was not the temperature of the actual solution.
Some modifications in this experiment could be as follows:
* A device that measures and provides the inside temperature of the actual solution should be included in the apparatus. This would provide a clearer picture of the situation.
* The rate of release of bubbles is allowed to stabilize first, because the readings can otherwise be misleading. For example, whenever hot water is mixed into the water bath, bubbles are released from the test tube with side arm. These bubbles are the carbon dioxide bubbles from the reaction. They are the consequences of the expansion of air that takes place in the test tubes.
Reference: The following resources were used for the experiment and its write-up:
* ” New Understanding Biology for Advanced Level- Fourth Edition” by Glenn and Susan Toole