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Investigate how temperature affects the rate of anaerobic respiration in a sucrose & yeast solution.

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Introduction

Investigating the Fermentation of Yeast Aim: To investigate how temperature affects the rate of anaerobic respiration in a sucrose & yeast solution. Hypothesis: Temperature will affect the action of yeast. The rate of respiration will increase with temperature until the heat becomes too much & the enzymes in the yeast are denatured. Very low temperature will slow the rate of respiration & make the enzymes dormant/inactive. Theory: Yeast lives as single cells, its name 'saccharomyces' means sugar fungi. It is a fungus which acts as a biological catalyst. It has been used for many years in the process of fermentation. It is added to rice & barley to produce beer by anaerobic respiration. It is also used in dough, where it ferments in heat with the sugar forming carbon dioxide gas, which therefore causes the dough to rise. When added to a monosaccharide sugar (e.g.-Sucrose, Maltose, fructose, glucose etc.) it acts as a catalyst speeding up the reaction of anaerobic respiration (fermentation). The equation for anaerobic respiration is: Glucose (C6H12O6) --> Energy (ATP) + carbon dioxide (6CO2) + alcohol (2C2H5OH) It acts as a catalyst due to the enzymes it contains. Enzymes are substances made of amino acids that join with specific substrates to break them down. They have weak bonds joining them which can be easily broken. High temperature for instance will deform the active site & denature the enzyme. ...read more.

Middle

Control: * Only have one variable - temperature. * Control all other factors - pH of solution, concentration of solution, amount of air and solution in syringe. * Repeat each experiment twice for accuracy. * Use largest ice cream container possible to minimise lose of heat. (closest possible surface area:volume ratio to minimise lose of heat via diffusion) Uncontrollable Factors: * Slight lose of heat over the one timed minute- minimised by the use of a large container & the test only being timed for a short period. * Solubility of CO2 - carbon dioxide is very slightly soluble, 0.1688g per 100g of water (at room pressure & temperature) Results of the experiment: Temperature of water in container (�C) Number of bubbles CO2 produced, test one Number of bubbles CO2 produced , test two Average number of bubbles CO2 produced 8 0 3 1.5 22 9 8 8.5 32 12 13 12.5 45 42 42 42 58 64 72 68 85 11 10 10.5 (See Next sheet for line graph of results) Analysis: The results that were collected, shown on the graph on the following page, illustrate that my hypothesis was partly correct. The graph shows how the rate of respiration increased with temperature until, by 85�C, it had slowed dramatically. This proves my theory, that the enzymes in yeast, like those in our bodies, e.g. amylase, are more active with higher temperatures, however are denatured if the temperature becomes too high. ...read more.

Conclusion

However, this method can only help the situation and not solve it. On the first test that we did, we took the temperature at the end of the minute to test for accuracy in variation of temperature, only to discover that the temperature still changed by approximately 2�C. The only way to really solve this would be to use an electrically operated, thermostatically controlled water bath. However, this would make controlling the rest of the experiment much more difficult as it is a large, cumbersome device and it would be difficult to set up the equipment effectively. A final factor that I would change is a piece of equipment that we used- the syringe. Using tongs to hold the syringe in place under the water was necessary To prevent scalding however it made controlling the angle the syringe was held at difficult. The design of the syringe meant that any slight tilt off of horizontal caused solution to spill out into the container. One way to correct this would be to use less solution in each syringe so that the level of solution was further from the opening in the end. e.g.- Conclusion: Considering the means we had to carry out this experiment. ( i.e.- the equipment etc. ) The experiment went very well , however there are many areas of the method that could be improved upon to consequently get much more accurate results to not only be able to prove the hypothesis but also to be able to conclude on exact temperatures at which the enzymes become dormant, most active & finally denature. By Louise Martin 10ME ...read more.

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