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Investigation into the Effect of Temperature on the Rate of Fermentation by Yeast.

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Introduction

INVESTIGATION INTO THE EFFECT OF TEMPERATURE ON THE RATE OF FERMENTATION BY YEAST Aim To investigate the effect that temperature has on the rate of fermentation by a yeast solution. Theory Yeast is a microorganism, and like all cells, gets its energy from respiration. There are two types of respiration: aerobic, and anaerobic. Aerobic respiration involves oxygen, and carbon dioxide, water and energy are produced when oxygen and glucose are reacted together during respiration. Most living organisms respire aerobically, but yeast does not; it respires anaerobically. This means oxygen is not used when glucose is converted into energy. This process is fermentation, and is when yeast does. The equations for a fermentation reaction can be seen below, as GCSE Biology by DG Mackean1 tells us: glucose alcohol + carbon dioxide + energy C6H12O6 2C2H5OH + 2CO2 + energy When yeast is used in fermentation, carbon dioxide is produced, as a gas. The "rate at which carbon dioxide is produced can be used to measure the rate of anaerobic respiration of yeast", says Practical Biology by Roberts, King, and Reiss2. This means that the rate carbon dioxide is given off at from a fermentation reaction involving yeast will indicate the rate that the yeast if respiring at. Enzymes need several conditions to be just right for them to be able to work at the optimum. The pH of the solution yeast cells are in is one factor that affects the rate of respiration - most work best at pH 7; yeast and enzymes also need specific temperatures to work efficiently at - 45 oC is approximately the optimum temperature that enzymes work at. The rate of reaction of enzymes increases as the temperature increases, up until 45 oC - the optimum temperature - and after that the enzymes begin to be denatured, and cease to work as normal. This means that their rate of respiration increases as the temperature increases up to about 45 oC, but after that, the rate of respiration decreases.

Middle

There was no carbon dioxide released whatsoever during this experiment, as can be seen from the table. This shows us that at 0 oC, there is no cell respiration taking place, and so no carbon dioxide is being produced. No cell respiration is taking place because the temperature is too low for the cells to be able to be active, so no energy is used, or needed. This result supports the prediction that at '0 oC, there will be no CO2 produced'. Table 3 shows the results from the 15 oC experiment. The start volume was 1 cm3, and no carbon dioxide was released during this experiment either, which can be seen by the volume of CO2 released. There was also no cell respiration taking place at this temperature, again because of the low temperatures, meaning that no activity is taking place, and so no energy from respiration is needed. This supports the prediction that 'at 15 oC, there will be no carbon dioxide produced'. The experiment using 30 oC as the temperature at which the reaction took place, produced carbon dioxide, and the results can be seen in Table 4. The start volume was 1 cm3, and so subtracting 1 from all the readings has found the volume of CO2 produced. Because carbon dioxide was released during this experiment, we can say that cell respiration was taking place, because the temperature was warm enough to give the yeast molecules enough energy to move around, and therefore have the need to produce energy to do so. The carbon dioxide was produced quickly at first, and towards the end of the experiment, the rate of production of carbon dioxide slowed. This is because the glucose in the solution was becoming used up, so CO2 was produced while the glucose was readily available, but as it became more scarce, the production of energy became less, and so the release of carbon dioxide was less.

Conclusion

Improvements to the method A larger gas syringe could have been used, so that the experiment could have been carried on for longer in the 30 oC and the 45 oC experiments without the syringe having to be pushed back to the beginning of the outer tubing once 100 cm3 of CO2 had been collected. This added inaccuracy to the experiment, and meant that we could not use the readings that were taken after 100 cm3 of CO2 were collected. If we used a larger syringe, this would not be a problem, and the 30 oC experiment would also have been able to be carried on for longer. The range of measurements about the 45 oC mark could have been increased. This would have narrowed down the exact temperature at which the yeast released the most carbon dioxide. The concentration of the yeast in the solution could be increased or decreased, and the effect of this could be investigated. The concentration of the glucose could also be changed, and how this affected the release of CO2 could be explored. Improvements to provide additional evidence The effect of using another source of energy on the release of carbon dioxide could be investigated. This would involve replacing the glucose with sucrose or fructose. We could also investigate the role that the type of yeast has to play in the production of carbon dioxide during respiration. This could be done by using fresh yeast instead of dried yeast, or Brewer's Yeast. The energy changes involved in fermentation could also be investigated, by measuring the energy taken in or given out by the fermenting solution. The alcohol content of the remaining solution from the experiment could also be investigated. The effect of different types of yeast on the alcohol content could also be investigated. 1 GCSE Biology Second Edition; DG Mackean; page 20 2 Practical Biology; Michael Roberts, Tim King, and Michael Reiss; page 83 3 Biology New Edition; Mary Jones and Geoff Jones; page 15 - 1 -

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