The effect of temperature on the survival of yeast cells

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Sehar Ayyub                 Candidate number: 1102

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Biology Planning Exercise – The effect of temperature on the survival of yeast cells

Aim: To investigate the lowest temperature that kills all the yeast cells in a sample of yeast.

Scientific Background

Enzymes tend to work best at an optimum temperature (the temperature at which the reaction is most rapid) which varies depending on the enzyme and the conditions it requires. The general rule for enzymes is the higher the temperature the faster the reaction. However this is only up until a certain point where the enzyme begins to denature. An enzyme denatures when the temperature is above the optimum temperature for the enzyme and it begins to vibrate violently so all the bonds which make up the tertiary structure of an enzyme break therefore changing the shape of the enzyme making it unable to function. (The enzyme which catalyses this reaction is dehydrogenase)

Enzyme performance depends on the active site, an area on the enzyme molecule in which the substrate fits into. This is what makes enzymes very specific as each enzyme only catalyses one reaction.

Enzymes are tertiary globular proteins and their structure is held together by different types of bonds the strongest; the disulphide bridge which forms when two sulphur containing cysteine residues react together. Hydrogen bonds are also present in enzyme structure which bind the substrate to the active site and are relatively weak.

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Yeast, which is a fungus, respires anaerobically and anaerobic respiration involves energy release in the absence of oxygen, it therefore requires a hydrogen acceptor which in this case is Methylene Blue, an artificial hydrogen acceptor that accepts the Hydrogen from the sugar solution. Methylene Blue turns colourless when exposed to a reducing agent, therefore if it turns colourless it is implied that the yeast cells are actively respiring.

Hypothesis:

Assuming that yeast cells are alive at 35˚C  the optimum temperature can be predicted to be higher than this therefore the lowest temperature at which all the ...

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This is a well written introduction to a report. 1. The background knowledge section is well written but the sources need to be referenced. 2. The hypothesis is sound. 3. The results are well presented. 4. The report needs to be finished by including the main set of results, a conclusion and an evaluation. ***