Designing a data collection strategy The effect of temperature on the rate of respiration of yeast.

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Mahsa Chadry

Skill A – Designing a data collection strategy

The effect of temperature on the rate of respiration

Aim

I am going to investigate the question, does a changing temperature have an effect on the rate of respiration in yeast cells? A simple and safe experiment will be conducted by changing the temperature of the yeast and glucose solution, and recording the amount of carbon dioxide produced. Various temperatures will be created in a thermostatically controlled water bath, and a range of temperatures will be used to make the experiment as reliable as possible.

Prediction

I predict that with every 10⁰C, the amount of gas which is produced will be doubled. The Q10 of yeast is 2, therefore with every 10⁰C increase, it will double the rate of reaction, increasing the amount of gas made by 2.1 Q10 is the respiration rate at 10⁰C/respiration rate at t⁰C. I believe this will happen because, as the temperature rises there is an increase in kinetic energy of the enzymes in the yeast cells which creates more chances of enzyme substrate complexes being formed, because  there are more collisions happening between the enzymes and substrates. This in turn will increase the reaction rate and more carbon dioxide will be produced. So I believe that as temperature increases there will be more gas produced.

Each reaction has an optimum temperature where the maximum amount of enzyme substrate complexes will be created, with this experiment I predict it to be around 35⁰C.2 But eventually it will plateau off, such as at 50⁰C, once enzyme activity is at its highest and can no longer increase because there is a limited amount of substrates available. Also at high temperatures the 3D globular protein can denature because between the R-groups on amino acids which have a specific tertiary structure, hydrogen bonds or ionic bonds break. This happens because there is too much kinetic energy so there is more vigorous vibrating; breaking the bonds, and changing the active sites of the enzymes, meaning the complementary substrate cannot fit, leaving less or no enzyme substrate complexes being able to form. However it is not just the temperature that affects the rate of reaction, the concentration of glucose is a factor that can change the amount of gas produced. This is because with higher concentrations of glucose more substrates will be present in a unit of glucose making the optimum level of enzyme substrate complexes created a higher value.3

Respiration reactions all have a catalyst, which is an enzyme; in this case the enzyme present is in yeast. When aerobic respiration is taking place decarboxylase and dehydrogenase are the catalysts (enzymes) used in the link reaction to remove carbon by creating carbon dioxide and reducing coenzymes NAD to reduced NAD. This occurs in the matrix of mitochondrion, the site of respiration in cells. Here substrate pyruvate becomes acetyl Co.A, which is then used in the Krebs cycle, where carbon dioxide in once again produced whilst NAD is reduced. 4

Variables

Data collection

I will be collecting my data by conducting a water displacement experiment, where yeast reacts with glucose to produce carbon dioxide. I have chosen to use yeast as the organism containing the enzyme for my investigation, this is because yeast is a small simple organism which is easy to handle and can produce results efficiently due to a quick reaction rate, which was shown in a water displacement experiment completed in class. I have not chosen to use maggots as they have more variable factors which can change results, such as in the incident of a maggot dying, the respiration rate will decrease as there is one less organism that cannot be replaced.5 

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The respiration rate could be measured by a counting bubbles method, where bubbles created are counted during the reaction as they are trapped under water and float to the top of the surface. 6 However this method relies heavily on human perception making it very acceptable to human error giving false results. I have chosen to collect the gas of the reaction in a burette, whilst the solution is sitting in a thermostatically controlled water bath, with a magnetic stirrer. I found information from a website which told me that using a burette would be better than using a gas syringe when ...

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