The effect temperature has on the rate of anaerobic respiration in yeast.

Aim: To investigate the effect temperature has on anaerobic respiration in yeast.

Prediction: I predict that as the temperature of the water rises the faster the enzymes in the yeast will break down the glucose, therefore producing more carbon dioxide and more anaerobic respiration will take place. But when the temperature gets above at least 72c I predict that the enzymes in the yeast will stop working and there will be a decrease in the amount of carbon dioxide being produced and less anaerobic respiration taking place.

Anaerobic respiration is respiration without oxygen. Yeast can respire with or without oxygen in this case the yeast is without oxygen.

When it respires without oxygen it is called fermentation. The chemical formula is Glucose Alcohol + Carbon Dioxide + Energy.

Because of my scientific knowledge I know that yeast enzymes only ferment in sugar and flour (we are using sugar). I also know that temperature effects the rate at which enzymes work, making them move and work faster on the substrate (in this case is sugar), because heat produces energy. The diagram below shows the lock and key theory of enzymes the substrate has to fit exactly into the enzyme other the substrate can not be broken down.

I know that the enzymes will stop working at 72c because enzymes are proteins and at high temperatures the active site of the enzyme will start to change shape (denature) so the substrate can't fit in the enzyme therefore the enzyme cant break down the substrate.

In the past I have done experiments, which have proved that heat effects the rate at which enzymes work. I will explain the method of an enzyme experiment I did in the past. It showed how lipase is effected by heat when it breaks down fat. The fat shows up red on an indicator before lipase has broken it down. When it has been broken down it turned yellow. We put Lipase and animal fat in a tube, which was in a water bath so we could control the temperature. At 40c the colour of the indicator turned yellow, it turned orange at 10c and 60c and at 0c and 100c it stayed red. This showed us that the lipase enzymes worked best at 40c and didn’t work at all at 0c and 72c.

This backs up my prediction because it shows how the higher the temperature the faster enzymes work until a certain temperature which 72c.

Equipment: Water bath, 10ml syringe, 5ml of yeast and glucose solution, measuring cylinder, beakers, stop clock, thermometer and rubber gloves.

Method:

Heat water in water bath by turning the knob on the side of the water bath. If the temperature is meant to be at room temperature, check temperature of room than heat the water to that till temperature. Check temperature of water with thermometer.

Fill 10ml ...

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This backs up my prediction because it shows how the higher the temperature the faster enzymes work until a certain temperature which 72c.

Equipment: Water bath, 10ml syringe, 5ml of yeast and glucose solution, measuring cylinder, beakers, stop clock, thermometer and rubber gloves.

Method:

Heat water in water bath by turning the knob on the side of the water bath. If the temperature is meant to be at room temperature, check temperature of room than heat the water to that till temperature. Check temperature of water with thermometer.

Fill 10ml syringe, with 5ml-yeast and glucose solution leave the rest of full of air.

3. Put on the rubber gloves to protect you from the heat of the water and then place the measuring cylinder in the water bath and then making sure there are is no air left in the measuring cylinder lift it half way out the water and then hold it there. Then as soon as you place the syringe under the measuring beaker start the stop clock.

Stop the stop clock when there is 2.5ml of carbon dioxide in the measuring cylinder. Do the test three times for each of the temperatures 25c, 37c, 50c, 72c and 80c.

Fair Test: I have ensured that my experiment is a fair test by:

Doing each experiment three times for each temperature
Measuring the Carbon Dioxide in a measuring cylinder instead of counting the bubbles.
Using a stop clock instead of counting
Using the water bath to heat the water instead of a kettle or Bunsen burner so the temperature of the water is consistent
Checking the temperature of the water bath with a thermometer to check the accuracy of the water bath
Placing the syringe directly under the measuring cylinder so the carbon dioxide doesn’t escape.
PH also effects the rate at which enzymes work. I am using water, which is neutral, so this will not effect the enzymes and the pH will stay the same through out the experiment.

Results:

Conclusion

The results from my test clearly show me that, the higher the temperature of the water bath the faster the anaerobic respiration takes place and more carbon dioxide is produce, until the temperature gets to 80c were the anaerobic respiration stops working.

From my scatter diagrams I can see that there is a vast in increase in carbon dioxide being produced when the heat is increased because the line of best fit has fairly strong negative correlation.

I tried to find a trend or a pattern within the average graph. Using my line of best fit I found out how much time it took to produce 2.5ml of carbon dioxide for every 10c. Here is the table of results for every 10c.

I then calculated the difference in time between each 10c

When I round each difference to the nearest 10 the pattern becomes much more clear; 20c=20secs 30c=50secs 40c=50secs 50c=20secs 60c=50secs 70c=50secs

There is now a clear pattern. For every 10c there time difference goes from 20secs to 50secs to 50secs to 20secs, the pattern might repeat its self but there is no evidence to prove this because I didn’t obtain enough results. The pattern in the results shows an increase of anaerobic respiration as the temperature increases. The bigger the difference between the temperature the faster the rate of anaerobic respiration is taking place. The differences should keep on increasing but the difference decreases at 50c then rises at 60c there is no explanation for this apart from incorrect results which is doubtful as the test was very accurate.

On an average the difference in time increased at 35 seconds per 10c.

The results from the test prove my prediction to be correct, because when the temperature of the water bath increased so did the rate of anaerobic respiration until 80c where the anaerobic respiration stopped working. This is because the enzymes where getting denatured by the heat and their active site was being destroyed. I should have choose the temperature 72c instead of 80c so my results could support my prediction even more and check if my scientific knowledge is correct

This is because temperature effects the rate at which enzymes work, making them move and work faster on the substrate (in this case is sugar), because heat produces energy. Eventually when the surrounding of the enzymes get too hot the enzymes start to denature and they no longer have a use because the substrate doesn’t fit in the enzyme.

Evaluation:

I ensures safety in the experiment by using goggles to protect my eyes and rubber gloves to protect my hands from the heat of the water when I held the syringe underneath the water. I think the quality of my evidence was very accurate because the equipment I used ensured the stability of the temperature and the measurements in test were very good. For example I used a water bath to ensure the temperature would stay the same through each experiment. If I used a kettle or Bunsen burner to heat my water then the temperature would not be consistent and only stay at one temperature for a certain amount of time. I also used a measuring cylinder to measure the amount of carbon dioxide instead of counting the bubbles that leave the syringe.

This is more accurate because the bubbles come in different sizes and you could miss count them. The bubbles leaving the syringe were actually oxygen because the yeast and glucose solution was at the back of the syringe so the carbon dioxide was pushing the oxygen out of the syringe.

This doesn’t effect the test, as the amount of oxygen leaving the syringe was equivalent to the carbon dioxide being produced.

I used as much computer technology as possible to ensure accurate results. I used a stopwatch and an electronic water bath.

My evidence from my results was sufficient to support my conclusion because it clearly proved the amount of carbon dioxide produced increased as the temperature increased. My scatter diagrams, line of best fit and tables ensured that the evidence was clear although I thought I could have used more than one type of graph to show my evidence.

To improve my investigation I would have used a wider verity of graphs and charts to show my results. I would have tested the pH of the water bath before each test, so I knew it was neutral. I would do this because pH is another factor like heat that effects enzymes rate of work.

I would like to use to do another investigation exactly the same as this one but using the variable as pH instead of temperature.

Maybe then the experiment would give clear results, that show more patterns and trends that are easier to analyse and understand.