An Investigation Into the Effect of Temperature On Respiration In Yeast.

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AN INVESTIGATION INTO THE EFFECT OF TEMPERATURE ON RESPIRATION IN YEAST

Planning

Aim

For my coursework I am going to investigate the effect of temperature on the rate of respiration of yeast. My aim is to find out if there is any correlation between the rate of respiration of glucose by yeast and the mixture's temperature. I shall do this by conducting a simple safe experiment, which will involve the timing of the yeasts respiration, when mixed in a glucose solution. This shall be done at various temperatures.

To obtain the best range of values to use in my final experiment, I shall conduct a preliminary experiment on the concentration of glucose solution. In this way I will also be able to increase the accuracy of the final experiment by seeing if the effect of glucose solution on yeasts respiration will have any effect on the main experiment.

Variables

In my main experiment, I am going to use temperature as the changing variable.

Here is a list of variables that I am keeping constant.

* Amount of yeast

* Concentration of glucose solution

* Amount of glucose solution

Hypothesis, Theory and Scientific Knowledge

Temperature

There are many ideas to suggest that the change in temperature will cause an increase of respiration in yeast. Yeast is a single celled fungus made up mostly of protein, which is used in fermentation. Fermentation is the breakdown of sugars by bacteria and yeast using a method of respiration without oxygen (anaerobic respiration). It involves a culture of yeast and a solution of sugar, producing ethanol and carbon dioxide with the aid of the enzymes. The alcohol produced has been used in making wines and beers and the carbon dioxide produced has been used in baking as it gets trapped in the dough and causes it to rise.

Enzymes are catalysts that speed up reactions; they are made from protein and are specific as to which substrate they work on. For example a zymase-complex enzyme will only bind with a glucose molecule to produce the ferments carbon dioxide and alcohol.

Yeast has to make energy, stored as ATP to carry out all cellular functions. To do this they respire. They can respire both aerobically (when there is plenty of oxygen and the cells reproduce rapidly), or, where oxygen is short, they can respire anaerobically; in this process they are called partial anaerobes. This is because less energy is released as the glucose sugar is only partially broken down, but still keeps the yeast alive. In my experiment the yeast is respiring by anaerobic respiration.

Here is the equation for anaerobic respiration:

Enzymes in cytoplasm

(Zymase complex)

Glucose -----------------> ethanol + carbon dioxide +energy

C6H12O6 2C2H5OH CO2

The Kinetic theory states that, with an increase in temperature, the rate of reactions will increase. This is due to the increase of speed of the particles, brought about by the extra energy given to them by heat. The faster particles will bring about more particle collisions and so the reaction will take place faster. Enzymes are sensitive to temperature changes up until a certain temperature and will increase in their activity up to this point. The reactions that take place in the enzymes will be quicker and so will create more of their products. In general, it has been said that there is a doubling of the rate of reaction for every 10ºC rise this is called the 'Q10=2' theory. This should be evident when the concentrations of the yeast and glucose solution are kept the same also.

But once you reach a certain temperature the rate of respiration slows down and drops. This happens because; all the enzymes are made up of protein chains of amino acids. They exist in the form of a helix structure with hydrogen bonds holding them together. When heat is applied to the enzyme, energy is given off. The active enzyme cell deforms and the hydrogen bonds break, denaturing the yeast enzyme. It would not be able to function as usual, and this process is irreversible. This process is therefore called denaturising. The optimum temperature in which yeast enzyme work best is around 37ºC, below this the rate of reaction is slow and above 45ºC the yeast enzyme would denature.
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The analogy of denaturing is to compare a key to a keyhole. If the keyhole has changed, the same key will not fit in any more, and the lock will not be unlocked. The same thing happens when the yeast enzyme is denatured, therefore fermentation cannot continue after this has occurred.

Firstly though, I am going to carry out the preliminary experiment to see whether the concentration of glucose solution will affect my main experiment.

Preliminarily Work

Prediction

As the concentration of the glucose solution goes up the more bubbles of gas will ...

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