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The aim of this investigation is to find out how concentration of glucose affects the respiration of yeast.

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Scott Mabbutt Biology investigation: Investigating the effect of glucose concentration on the respiration of yeast Aim The aim of this investigation is to find out how concentration of glucose affects the respiration of yeast. Introduction Yeast are a single cell species of the kingdom fungi, and has commonly utilised by humans to produce bread, wine and beer for thousands of years. In order to produce the energy that yeast needs to perform cellular processes, it has to metabolise glucose. Essentially the Glucose is turned into energy in the form of ATP. I plan to investigate how the concentration of the metabolic substrate affects the rate at which it is metabolised. I will do this by measuring the gas given off as a by-product of respiration, CO2. I will hope to gain quantitative evidence to back up a prediction I make. The equipment I will need is: * Test tubes x 6 * Boiling tubes x 6 * Pipette * Temperature controlled water bath * Spatula * Yeast up to 100g (dried) * Water 1dm * 500g Glucose (powdered) * 10cm3 Measuring cylinder * 100cm3 Measuring cylinder * 100cm3 Beaker x 5 * 500cm3 Beaker x 2 * Thin tipped Semi-permanent marker pen * Digital Timer (measures accurately to 1/100th of a second The variable I aim control are type of sugar substrate, temperature, pH and enzyme concentration. The type of sugar I am using will be controlled easily by the fact that I will make sure that no other sugar than glucose is used in the reaction. This is because if a different sugar contaminates the reaction the yeast may respire that sugar at a different rate to that of glucose. I will control temperature by the use of a temperature controlled water bath. The water in the bath will be heated to 40oC, by an internal element heater. This will be connected to a thermostat that will make sure the temperature will stay at the correct temperature. ...read more.


All my readings will be taken to a suitable degree of accuracy. Therefore all measurements will be done to the nearest 0.1cm3. This also to all calculations I make. Hypothesis Will the rate of reaction increase with substrate concentration? I predict that as the substrate concentration increases, the rate of reaction will also increase. This will do this up to a point where increasing concentration will no longer increase the rate of reaction. Theory Justifying Hypothesis There are two main areas of biology behind my prediction. One is factors affecting enzymatic activity and the other is factors affecting Glycolysis and the Ethanol pathway in yeast. One of the factors affecting the rate of an enzyme controlled reaction is substrate concentration. In the case of this reaction, there are numerous enzymes, but the initial substrate is Glucose. The concentration of glucose is the amount of Glucose in a given volume; for the purpose of this experiment it is in 10cm3. In order for a reaction to take place there needs to be a collision between the substrate and the enzyme. The more molecules of substrate there are in a given area, the more chance there is of a random collision with the active site of an enzyme, and it is therefore more likely to form an enzyme-substrate complex, and hence be reacted. The diagram below shows how changing the number of units per volume. To form an enzyme-substrate complex the substrate must exactly fit into the active site of the enzyme. The reason for enzymes being so abundant in living organisms is that they lower the activation energy of reactions. They do this when the complex is formed and the enzyme shape applies pressure to certain bonds in the substrate and make it easier to break these bonds, thus requiring less energy. The diagram below summarises the reaction: 3. The theory on which enzyme reactions is based is called the lock and key theory. ...read more.


And also in measuring out solutions this can mean amounts are out be up to 0.1cm3. However I feel that such errors are small enough to be considered irrelevant. To further extend my investigation I could use more repeats at extended amounts of concentrations to see if the graph would level out. I could also compare how different respiratory substrates compare to glucose in producing a rate of reaction. I could use various sugars like sucrose, or I could use different fats or proteins. To further improve my investigation I could use different equipment that measured out things to a higher degree of accuracy this would make me more certain of my data. I could also use a different method of obtaining a rate of reaction. Instead of finding how much gas was given off after 20 minutes, I could measure the gas given off at time intervals and making a graph of gas given off against time, then finding the initial gradient of these lines and using that as the rate. This can also be used to justify how enzymes work. The initial increase in gas given off is steep. This increase then slows down and eventually plateaus off when all the substrate is used up. The concentration when the initial gradient of the graph is no longer increasing would be when the reaction has reached Vmax. Another improvement could be to use an activator like orange juice or yeast extract to make the yeast more active. This would help get more substantial amounts of gas to analyse. Another method of collecting gas could be to use a manometer. This is a thin tube that when filed with water moves along a measuring device when gas displaces it. This could be used to see how much was given off in a more accurate way. Overall I feel that even with one erroneous result, my data and results are good enough to make a firm conclusion as the errors were not significant enough to make a difference to the accuracy of my results. ...read more.

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