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Investigation into the Effect of Temperature on the rate of Respiration of Yeast

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Introduction

1 Sean Sandford11B Biology Coursework- Investigation into the Effect of Temperature On the Rate of Respiration of Yeast Preliminary Work For my preliminary work, I am working with 35ml of yeast. I think that this is the best volume to use as it is about 3/4 of a test tube full, and it allows for the yeasts expansion when heated. I am trying to find out the best range of temperatures to be used in finding out the respiration of the yeast, and I am also trying to find an equilibration time that can be used in the main experiment, as the time taken for the yeast to heat up to the desired temperature. Apparatus - One beaker - Two test tubes - Delivery tube with bung - Yeast (35ml) - Water - Stopwatch - Thermometer - 35ml syringe Method 1. A beaker was filled with water then heated to the desired temperature. 2. A test tube was then filled with 35ml of yeast and placed in the beaker of water. 3. The time taken for the yeast to heat up to the temperature of the water in the beaker was then measured using a stopwatch and thermometer. ...read more.

Middle

Prediction From the results of my preliminary work, I predict that between 20o and 40oC, the yeast enzymes will be respiring fastest because enzymes work best at room temperature. I also predict that as the temperature goes up, the respiration will get slower and slower because the enzymes will start to denature (the yeast enzymes stop working) at higher temperatures. This is shown in the graph on the next page: 4 Sean Sandford11B 40o is the optimum temperature because it is just the right temperature for the enzymes to be working at maximum rate. Yeast is an enzyme, which means that it is also a catalyst. Enzymes work using the 'lock and key' theory, where the 'key' fits into the active part of the enzyme (the 'lock') and the reaction takes place. The key then unlocks to form one or two more new substances and the enzyme is ready to bind with another of these substances. An enzyme can only bind with a substance that fits the shape of the active part of the enzyme, so, because the enzymes are sensitive to higher temperatures, the active site on the enzyme changes shape so much that binding can hardly take place. ...read more.

Conclusion

The key then unlocks to form one or two other substrates, and the enzyme is ready to bind again with one of these new substrates. An enzyme can only bind with a substrate that fits the shape of the active part of it, so, because the enzymes are sensitive to higher temperatures (in my graph any temperature below around 50oC) the active part of the enzyme changes shape so much that the binding can hardly take place. This is the denaturation, and it also means less respiration. As the temperature rises to 40oC, the yeast enzyme works at a faster and faster rate, because it is a catalyst and therefore speeds up reaction rate. This 'lock and key' theory is shown in the diagram below: 9 Sean Sandford 11B Analysis My conclusion does support my prediction to quite a large extent. The graphs both show that I predicted correctly the optimum temperature would be 40oC, and also that after this temperature, the enzymes would start to denature. At 40oC, the enzymes are working the fastest, colliding with the glucose molecules, and breaking them down to be used for respiration. The only difference between the prediction and conclusion is that I predicted that the enzymes would have completely denatured by 70oC, when in fact there was still some respiration. This shows that my conclusion supports my prediction to quite a large extent. ...read more.

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