How Does Temperature Affect the Rate of Respiration of Yeast?

Yeast has to make energy, stored as ATP to carry out all cellular functions. To do this they can respire both aerobically when there is plenty of oxygen, but where oxygen is short, they respire anaerobically; they are called partial anaerobes. This produces less energy, but keeps the yeast alive. Pyruvic acid has to be broken down in respiration when formed by breaking down of glucose molecules, this can't be done in the same way as it is aerobically when respiring anaerobically which is how the carbon dioxide and ethanol is formed through the zymase. Here is the equation for anaerobic respiration:

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. Faster particles will bring about more particle collisions and so the reaction will take lace faster. Enzymes are sensitive to temperature changes up until a certain temperature and will increase in their activity also. The reactions that take place in the enzymes will be quicker and so will create more of their products. As a general rule of thumb, 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 concentration of the enzyme and substrate are kept the same also.

Enzymes are sensitive to temperature up until a certain temperature where the shape of the active site is altered drastically, so much so that binding hardly ever takes place. This is called denaturisation.

Prediction

I predict that the yeast's respiratory rate of reaction should increase in speed as the temperature increases. However this may at some point peak and therefore from then on it will decrease in respiratory rate.

My reason for the above prediction is that yeast can respire both aerobically and anaerobically. In the experiment the yeast will be respiring anaerobically and breaking down the glucose stored in it as a waste product of this process it will also form CO2 and alcohol in the form of ethanol. This respiration process is called fermentation. The yeast breaks down the glucose using a series of enzymes. I think from this that the more glucose that is present in the yeast the more will be broken down and therefore more CO2 and ethanol will be produced as waste products at a faster rate until it reaches a certain temperature and the amount of CO2 will reduce.

Variables and Constants

Here is a list of dependant variables. These can have an affect on my experiment and this is how I will control them if possible.

Amount of yeast solution

Amount of glucose solution

Amount of shaking

Light conditions

Time

Apparatus

AMOUNT OF YEAST SOLUTION

The amount of yeast solution is crucial, more yeast means more glucose will be respired and more products created. An imbalance will upset the results. The yeast solution will be measured out each time using a measuring cylinder to make sure we have the same amount every time.

AMOUNT OF GLUCOSE SOLOUTION

The amount of glucose solution will affect the results also, as more glucose would speed up the experiment, and therefore not make it fair. The glucose will be measured out each time using a measuring cylinder to make sure we have the same amount every time.

AMOUNT OF SHAKING

Shaking will help to activate the yeast. If it is not mixed properly the solution will take a long time to start the reaction and the results would not be fair. I will shake the test tube at the start to make sure all the yeast solution is mixed.

LIGHT CONDITIONS

These would not have a great deal of affect on my experiment and are beyond my control. Some of the substances may be sensitive to these, but I doubt they are sensitive enough to affect my results.

The only independent variable that I'm going to change is the temperature. I am going to start at 20° and increase it by 10° each time, up until 60°.

Apparatus List

00ml yeast solution

20ml glucose solution

Measuring cylinder 100ml

Gauze

Heatproof mat

Bunsen burner

Gas syringe

Side arm conical flask 250ml

Large beaker

Thermometer

Tripod

Clamp stand and clamp

Stopwatch

Method

* Set up apparatus as shown in the diagram.

* Get the water to the correct temperature using the bunsen burner in the large beaker.

* Put the yeast and the glycos into the conical flask.

* Place the conical flask in the water bath.

* Put the bung in the conical flask.

* Start the stopwatch.

* When the stopwatch gets to five minutes.

* Attach the gas syringe to the conical flask.

* Start the stopwatch and after another five minuets.

* Write down how much gas has formed in the syringe.

Safety

While doing the experiment I must be careful of hot water, thermometer, bunsen burner and the large glass beaker. I will protect myself by wearing safety goggles and a lab coat throughout the whole experiment. If I spill anything then I will soak it up using a cloth immediately.

Results

Temperature

Volume of gas cm3

Rate

st

2nd

3rd

Average (5mins)

min cm3

20°

21

29

20

23

5

30°

87

55

59

67

3

40°

45

40

10

32

26

50°

77

35

60

57

1

60°

42

00

48

63

3

Observations

I could see a reaction happening between the yeast solution and the glucose solution. I saw it all frothing up with lots of air in between the solution.

Conclusion and Analysis

I have found that as I increased the temperature of the yeast solution, the rate of respiration increases. The temperature that I got the most CO2 was 40°, after this the enzymes seemed to be de-natured and the rate of reaction slowly decreased. I could see how much CO2 had been produced by looking at the reading on the gas syringe.

Analysis on Results

I have also found out that the Q10=2 theory does work, but not exactly. My result probably weren't accurate enough to prove this exactly but it worked enough.

Evaluation

I kept the same water in the water bath so as to keep it a fair test. I took all precautions to make the apparatus used to be reliable and give good values so I think the slight unreliability was caused by the preparation of the solution and the 'unpredictability' of how the reaction went in the solution. I have ensured that my results are accurate by controlling all the variables stated in my Planning. I also took care when using the equipment so as to retain it the same throughout the experiment. For this, I checked everything was set up correctly at the beginning of each new temperature in the same way.

To obtain more reliable results I would want to:

* Measuring the same amount of dried yeast on scales and to measure the water in a measuring cylinder to make sure I use the same concentration of yeast and water.

* Prepare the yeast solution at the same time and leave at the temperature.

* Not activating the yeast so as to prevent any getting a 'head start' over the others.

* This would ensure that all the preparations are the same and would give continuity.

This would help give more reliable results throughout.

I think my results are quite reliable for the level that I did the experiment at. They proved that my prediction was right so they must have been fairly reliable but not very accurate. But I would not go and publish these results.

I would probably want to calculate the point where the enzymes begin to stop respiring in yeast. At this stage, I shouldn't think there is to be much more I could do. I wouldn't want to investigate any other variables or reactions at this time.

By looking at my graph I found two anomalous result, I have circled them in red to show where they are. I think the two points are anomalous because they should have decreased in the amount of CO2 produced not increased. These could be that different groups of people were doing the experiment. The group that did the experiment for 60° might have used a different make of syringe or it might have happenedthrough human error.

Bibliography

Books

Co-ordinated science biology Beckett Gallagher

Work out science Michael and Janet Major

Science for GCSE Graham Hill

Biology for life M.B.V Roberts

Websites

Britanica.com