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Biology Coursework: Respiration in Yeast Planning Aim The goal of this experiment is to discover how varying the temperature, of a solution of yeast and sucrose, will affect the amount of carbon dioxide produced during a set time period. After I have completed this experiment and obtained enough data, I will analyse and discuss it, and then I will evaluate it. For this experiment, my independent variable will be the temperature, which I will change by adding warm water to it. My dependent variable will be the amount of carbon dioxide given off. My controlled variable will be the amount of sucrose and yeast there is in the solution, and also the time the experiment will be running for, as these are the only factors that can be varied to produce different amounts of CO2. Background Knowledge This experiment involves enzymes, which are biological catalysts. All the chemical reactions in a living organism are collectively known as the metabolism. Anabolic reactions normally need an input of energy, to build up large molecules from smaller ones. Catabolic reactions often release energy when breaking down large molecules into smaller ones. An example of anabolism is the condensation of glucose molecules, which happens in liver cells and skeletal muscle.
During this period, I will prepare for the next temperature, and prepare the yeast and sucrose as above. When the first test is over I will increase the temperature by adding some warm water to the cup from the kettle, to get it to he right temperature. In order to keep the temperature the same throughout the experiment, I will pour some of the hot water into a separate cup, so that I can pour some into the cup if the temperature should fall below a certain point. This should help to keep it a fair test. Safety is always a priority, and it is no different in this case. In this experiment there are no hazards to be wary about, other than the water from the kettle. To stay safe while pouring it, I will place the cup on the desk, and pour the water in slowly. I will also keep my bag out of the classroom, and the chairs under the desks. Prediction I predict that as the temperature is raised, then so will the rate of respiration. I believe that this will continue to happen up to an optimum temperature, at which the active sites of the enzymes will begin to denature.
The quality of my evidence is, overall, accurate and also reliable. This is because they follow scientific theory like the 'lock and key hypothesis' and the Collision Theory. It followed my prediction that was based on scientific theory. The results follow the expected pattern, which has reaches optimum temperature and then, when it starts to denature, the respiration rate falls. There was one set of anomalous results obtained in this experiment. This was when the temperature was at 30ºC. I believe these results to be anomalous as the do not follow scientific theory. At this temperature, the rate of respiration does not increase from the first set of results, which were at 20ºC. According to the lock and key hypothesis, a rise in temperature should increase the rate of respiration. This is not the case with this set of results. The rest of the results do, however, follow theory. On the next page there is a table commenting on how the experiment could be improved in order to gain more accurate results, and minimise the risk of anomalies. Possible sources of error/inaccuracy Ways to improve The collecting cylinder. Use one with smaller measurements. Solution not the right temperature. Leave time for the yeast to heat up before adding the sucrose and starting the experiment. The data I've collected is sufficient to draw the conclusion that my prediction was correct. ?? ?? ?? ?? David Hart Biology Coursework: Respiration of yeast -1-
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