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# Investigation of the effect of temperature on the rate of respiration of yeast.

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Introduction

Investigation of the effect of temperature on the rate of respiration of yeast Introduction The aim of this investigation is to determine the effect of temperature on the rate of respiration of yeast. The temperatures at which the culture was tested at were 20�C, 30�C and 40�C to give a range of rates of respiration which can be compared. The yeast cultures were maintained at these temperatures using a water bath as water has a high specific heat capacity and thus maintains a specific temperature relatively well. As a result of preliminary studies into the topic, the hypothesis was made that 'as the temperature increased, the rate of respiration would also increase in the yeast.' This is because the reactions that occur in respiration are enzyme catalysed. Therefore, we can deduce that any reaction where enzymes are present will have an optimum temperature at which the rate will be at its optimum. This is likely to be around the 30�C - 40�C. For example at the very first step of respiration in glycolysis, the enzyme phosphofructokinase is used to phosporylate the glucose so that it can be split into to two triose sugars that will eventually produce a pyruvate molecule each. When these pyruvate molecules enter the Kreb Cycle and is converted to acetate, coenzyme A combines with this new compound to assist in the formation of oxaloacetate. ...read more.

Middle

Just how much will a small change in temperature affect the Rate? If a reaction has an Activation Energy of 50 kJ/mole what effect on the Rate would a change of temperature from 20to 30oC? 1. Convert the two temperatures to Kelvin: T1 = 20+ 273 = 293 K T2 = 30+ 273 = 303 K 2. Plug in Activation Energy, T1,T2, and R = 8.31 J/mole-K into the Arrhenius Equation. ln (k2/k1) = [(50000 J/mole)/(8.31 J/mole K)](1/ 300 K - 1 /310 K) ln (k2/k1) = 0.647 k2/k1 = e0.647 = 1.91 Note that a 10 oC change in temperature results in an approximate doubling of the reaction rate which is known as the Q10 rule and it can be predicted to be the case in this reaction also. An actively respiring yeast culture will be placed in water baths at different temperatures and the rate of their respiration measured using a manometer and recording how much the fluid moves from its initial position after a time interval of five minutes. This will indicate how much gas is produced by the respiring yeast every five minutes at different temperatures. The rate of respiration can therefore, be calculated from these observations for each temperature and then compared to identify any trends. ...read more.

Conclusion

When these pyruvate molecules enter the Kreb Cycle and is converted to acetate, coenzyme A combines with this new compound to assist in the formation of oxaloacetate. Decarboxlases and dehydrogenases are also used in the Kreb Cycle. Then in the last stage of oxidative phosphorylation cytochrome reductase and cytochrome oxidase are used. Thus, as a result of all these enzyme catalysed reactions, the temperature will be a limiting factor and as the rate increases the most between 30�C - 40�C it can be said that the enzymes involved have their optimum temperature within this range. The prediction was also made that as the temperature increased 10�C the rate would double as a result of the Q10 theory. The experiment showed that this was not exactly the case as the rise of temperature from 20�C to 30�C resulted in an increase in rate by a factor of 1.68 and an increase in temperature from 30�C to 40�C yielded a rate increase by a factor of 1.34. although this is not a consistent factor of two that is being shown, its can be roughly approximated as such. This is significant because the Q10 rule is applicable under ideal condition that were too difficult to obtain in a college laboratory and thus discrepancies are noted. ...read more.

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