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Yeast Investigation

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Daniel Gillespie 11F Biology Coursework SC1 Introduction to yeast Yeast are unicellular fungi. It has been around for along time and has been involved in the making of bread, wine and other materials for man. Now yeast is used in many different industries for its fermentation properties. During this process in the industries the yeast is the waste product and is usually used for animal food or birdseeds. However the alcohol is the valuable product in the industry. Yeast has been a major material to man for a long time and is now a very expensive and profitable material for businesses and industries. The yeast respires to produce energy. When it does respire it produces and needs products and waste products, these are shown in the word equation below. To control this reaction the yeast has an enzyme; this enzyme is called zymase. Enzymes are used to control the speed and the rate of the respiration in the yeast, it changes the rate and speed by the environmental surroundings it is put in. glucose -----yeast---> ethanol + carbon dioxide + energy (210kj) C6H12O6 -----yeast---> 2C2H5OH + CO2 The reaction shown above is also called Fermentation. Fermentation is used in the brewing industry and the picture below shows how they ferment the sugar (glucose) in the yeast to make alcohol. Fermentation is the break down of sugars by using yeast to respire without oxygen (anaerobic respiration). The enzymes control the rate in which the yeast ferments, the enzymes control the rate of fermentation by denaturing the enzymes at certain environmental surroundings. This reaction is also used for making bread, producing cheese and yoghurt. In the beer industry there are many different types of yeast that are used to make the alcohol. There are yeasts known as 'Top-working yeasts' and 'Bottom-working yeasts'. A 'Top-working yeast' for example would be saccharomyces cerevisae and this would be used for making English beers and ales. ...read more.


The water in the beaker was measured at a certain temperature. These were the temperatures that we tested the yeast in. We tested the yeast in water surroundings at 50, 45, 40, 35 and 30 degrees C. We did this buy boiling a kettle containing water. We kept the kettle away from our apparatus as well as ourselves because spillages could have ruined our results but could have also caused a safety hazard and we could burn ourselves. So keeping the kettle away was a safety measure as well. We measured the water in to the beaker and our measurement was 250ml. However to get the right temperatures because the kettle had boiled the water we had to add cold water and take some of the hot water out to get it to our temperatures which we were going to test. The test tube that we set up was to be laid in the heated water in the beaker. In the test tube we had 20ml of yeast. We also had a bung with a glass rod going through it. Putting the bung into place on the test tube created a vacuum. This meant that if we put tap water into the top of the glass rod that it would stay in the glass rod and would not fall into the yeast in the test tube. This would then be used to obtain our results. Our results were to count the bubbles that came up through the test tube. This would indicate that a gas was being produced and the number of bubbles that came up the glass rod would indicate at what rate was the gas being produced. Once we had used our first set of apparatus to measure the rate at which yeast respires we then repeated our experiment for each temperature to ensure that our results would be accurate. This also brought up any floors in the experiment and our results. ...read more.


This was because the table was being knocked as people walked past making the salt solution jump up and down making it harder to read the results at the correct times. The temperature was also a problem with this apparatus as it had dropped by the time we had finished the experiment as it did in the beaker and test tube apparatus. I would probably try to change this experiment and put it in an oven at the right temperature like I mentioned above. Overall I would have made changes to both the experiment. One of these changes would have been the time that we measured the rate of respiration for. If I did this experiment again I would increase the time that we measure it for, I think this because I would want to investigate further if the temperature that the yeast was in was the easiest one for it respire in for long periods of time. However this would have made it harder as well because the water in the beaker would have gradually lost more and more heat and if we measured the experiment for 10 minutes it may have dropped about 15oC. Doing the experiment like this would have also been very time consuming because we would want to go through the experiment twice to check for any anomalous results. In both experiments I would have also tried to change the amount of water in the beaker. As we poured the boiling water in from the kettle we measured it however when we dropped the temperature by adding cold water the measured amount increase, and decreased when we poured water out. So we ended up with a measurement nothing like the one we had made at the start of the test with the kettle. I think that this is a flaw in the experiment as it could have changed our results slightly and made them more fair as well. The experiments that I have done I think have obtained accurate results and have also concluded most points made in my prediction. ?? ?? ?? ?? ...read more.

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