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BIOLOGY PRACTICAL-yeast and gas production

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Yeast and Gas production Planning (a) Aim: To investigate gas production by yeast in a glucose mixture. Theory: The process by which living organisms release energy from their food is called respiration. It is the oxidation or break down of glucose molecules to release energy. Respiration can be of two types Aerobic and Anaerobic. During Aerobic respiration glucose is burnt in the presence of oxygen to produce energy and carbon dioxide. However in Anaerobic respiration glucose is burnt in the absence of oxygen to produce energy and alcohol or lactic acid (animals). Yeast cells respire anaerobically to produce ethanol and carbon dioxide. Yeast cells have enzymes which are used in this process, Zymase enzymes. Enzymes are biological catalysts that alter the rate of reaction without being chemically changed during the reaction. They help to speed up the bio-chemical reactions in living organisms. Enzymes are substrate-specific. That is a particular type of enzyme only catalyses few reactions. This means that there are very less possible substrates that can combine with the active site of the enzymes. The active site of an enzyme is the region on the surface of an enzyme to which the substrates bind and are catalyzed by the enzyme. This active site has a particular shape and different chemical properties. Only the few possible substrates with the right shape and the chemical properties are attracted towards the active site and bind together to be catalyzed. ...read more.


To do this we have to change the yeast and glucose solution after each reading to make sure that there is no initial toxic that will be inhibit the yeast growth. Planning (b) Apparatus: * Yeast in a glucose mixture * Beakers * Boiling test-tube * Syringe 5ml * Plasticine * Test tube rack * Thermometer * Stop-watch Procedure: * First we fill a test tube with water at a particular temperature. (Varying from 20�C-65�C). * Then we fill a syringe 2ml of yeast and glucose solution and then with 1ml of air. * We then stick plasticine behind the syringe to make it heavy and completely be immersed into the water in the test tube. * After about 2-3 minutes of the syringe being immersed in water the stop watch is started and the number of bubbles produced in 2minutes is counted and recorded. * The experiment is repeated with water at different temperatures. This is how the apparatus, which has been set up, will look like. Data Collection: It took some time for the bubbles to start coming out and that's why we are asked to start counting after 2 minutes. After this time bubbles came out at regular intervals for each given temperature. The readings of this experiment are given in the table followed. If you observed the test tube for even longer time, the number of bubbles produced fall after a particular time. ...read more.


Another limitation could be that by mistake we might count the bubbles that come out when water is shook, and this might give us another faulty count and thus our results could be proved wrong. Precautions Always make sure that the ratio of glucose solution to that of the yeast remains the same as this is very important and mistakes might give faulty readings. See to that you don't waste a lot of time after adding the yeast to the glucose other than waiting for two minutes. If you wait any longer the digestion will occur and it is possible that you might not see any bubbles when you actually start taking readings. Modifications: * Next time I would take a fresh glucose and yeast mixture after each reading so that the solution or the condition of the yeast cells is the same for all the temperature readings. * Instead of counting the bubbles to measure the gas production I would collect the gas in a test tube and then measure its volume. This would give a more accurate reading for the gas production as the error due to the size of the bubbles is overcome. Conclusion Through the experiment we were able to determine our aim and out hypothesis was also verified and proved right through our observations. We also were able to find the optimum temperature for the yeast and at what rate it digested at. ?? ?? ?? ?? ...read more.

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