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# The rate of respiration in yeast and how it is affected by temperature.

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Introduction

The rate of respiration in yeast and how it is affected by temperature. Science Biology: Planning For my coursework I am going to investigate how temperature can change the rate of respiration on yeast. I shall do this by conducting an experiment which will involve the timing of the yeast, water and glucose. I shall time how long it takes for the yeast mixture to respire 10 bubbles. I have chosen yeast because it responds quite quickly so it doesn't take all day. When I chose yeast I was aware of the factors that will affect enzymes and living things. These are: * Temperature * Oxygen availability * Glucose availability * PH * Radiation (Not in my experiment) * Water * Concentration Preliminary Work I discovered that the PH in the experiment denatures the enzyme as do other enzymes and temperature. Anaerobic respiration is the production of carbon dioxide without the use of oxygen. So all living things need oxygen to aerobically respire and yeast is a living thing. As yeast aerobically respires it produces ethanol which gives us the smell of the alcohol. I am using glucose because it reacts with yeast. The preliminary experiment showed that as the concentration of the water and yeast solution to the fixed amount of glucose increases the rate of reaction and therefore produces more carbon dioxide, we measured this in how long 10 bubbles took to come out of the water. ...read more.

Middle

The products are released from the enzyme surface to regenerate the enzyme for another reaction. The specific action of an enzyme with a single substrate can be explained using a Lock and Key theory. In this theory, the lock is the enzyme and the key is the substrate. Only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme). Only the correctly shaped key opens a particular lock. The graph shows that as temperature is increased, the reaction rate of an enzyme increases. However, the graph shows that there is an optimum temperature where the reaction proceeds at its maximum. Above that optimal temperature, the reaction rate decreases. What happens can be explained in terms of kinetics, which essentially means molecular motion. All molecules are in motion. As the temperature increases, their motion increases too. In the case of enzyme catalyzed reactions, as the speed of enzyme and substrate molecules increases, the chance for collisions so they can form enzyme-substrate complexes increases. Thus as the temperature rises, the reaction rate increases too. Above the optimal temperature however, this does not apply. The reaction rate begins to decrease again because some of the enzyme molecules are now warm enough so that their shape becomes altered (denaturing the enzymes). As the temperature rises above the optimal then, an increasing number of enzymes become denatured. Fewer and fewer enzymes are able to fit with their substrates at the active site. ...read more.

Conclusion

I needed to put the yeast and glucose into the test tube, put the bung on to the test tube and start the stopwatch all at the same time. I also think it would have been better if I had used the same yeast and glucose from the whole experiment but was unable to due to the time restrictions. I had to conduct the experiment over a number of days and could not therefore use the same solutions. This is a source of error because the amount of time the yeast would have had already to respire the respiration of the yeast may have been different which may have produced an inconsistent rate of reaction. My results could have been more accurate because the results I obtained did not produce a good pattern on the graph. To remove this problem, I could repeat the experiment not only with three readings at each temperature, but also with three different solutions for each set of results, which would provide an even more accurate reading, as I could calculate an average. I would perhaps use a gas syringe instead of a boiling tube to make the reading more accurate. Maybe for a further investigation see what affects radiation has on yeast respiration. But that is hard because of the restrictions on the use of radioactive substances. I could maybe use methylene blue. I would time how long it takes to revert to the original colour using a control. This would be done at various temperatures to obtain the best range of values. ...read more.

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