The Respiration of Yeast.
Science Coursework
The Respiration of Yeast
Aim
To find out what the best temperature is for yeast to respire.
Prediction
To first make a prediction I need to know what yeast actually is. Yeast is a fungus, but with a difference, it consists of single cells and thrives in places where there is plenty of sugar (which is why sugar is included in this investigation). Yeast can carry out anaerobic respiration, known as fermentation. Knowing that yeast is a living thing I can predict that:
Yeast respires best at room temperature (35-37°C)
I came to this prediction because most living things do respire best at this temperature.
Yeast respires anaerobically, this is known as fermentation, the equation for it is:
Glucose Ethanol + Carbon Dioxide + Energy
C6H12O6 CO2
I can now also predict that bubbles of CO2 will be produced.
As I'm going to have high temperatures of water in this experiment I can predict that there may be a drop in the number of C02 produced because the high temperatures will denature the enzymes in yeast. The way in which it works is that:
Method
Equipment I will need for this investigation will be:
* Dried Yeast
* Rubber Bung
* Plastic Beaker
* Delivery Tube with bung
* 2 Boiling tubes
* Sugar
I first collected a beaker of warm water from the water bath and poured it into a boiling tube 1/4 full. I then put 1g of sugar to it, put a bung in it then shook until it dissolved. Then I put 1g of yeast in and did the same. Next I removed the bung and fit a delivery tube, ...
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Method
Equipment I will need for this investigation will be:
* Dried Yeast
* Rubber Bung
* Plastic Beaker
* Delivery Tube with bung
* 2 Boiling tubes
* Sugar
I first collected a beaker of warm water from the water bath and poured it into a boiling tube 1/4 full. I then put 1g of sugar to it, put a bung in it then shook until it dissolved. Then I put 1g of yeast in and did the same. Next I removed the bung and fit a delivery tube, I stood the tube in the remaining warm water in the beaker and placed the other end of the delivery tube into Tube B which was 1/2 filled with cold water. I waited 10 minutes to let the reaction take place after which I noticed a stream of bubbles coming out of the delivery tube (CO2). I recorded the amount of bubbles in 30 seconds and put it into a results table. Although CO2 bubbles were seen in the yeast mixture, Tube B was needed to show them clearly and make them countable. I then cleaned everything and repeated it but with different temperatures of water in the plastic beaker, the temperatures were: 20ºC, 25ºC, 30ºC, 35ºC, 40ºC, 45ºC, 50ºC and 55ºC. I chose precise measurements of the yeast using an electric balance to get precise and accurate results. To make it a fair test I had the same amount of measurements for everything in each experiment. Things that were controlled in the experiment were:
* Amount of yeast
* Amount of water
* Amount of sugar
This was to make it a fair test; this left the temperature of the water as the only variant. I measured the temperature of the water with a thermometer to get accurate readings.
Results
No. Gas bubbles given off (CO2)
Temp (ºC)
st Recording
2nd Recording
3rd Recording
Average
20
2
3
2
2
25
6
7
5
6
30
20
22
21
21
35
27
26
26
26
40
33
33
32
33
45
38
37
38
38
50
27
26
25
26
55
1
0
9
0
I chose this range of measurements to show clearly the best temperature that yeast respires at; from this I can plot a graph to further clarify the best temperature. Several experiments were done, and an average was taken to get more accurate and precise results.
Conclusion
Firstly from the graph I can see that
* The peak is at 45ºC
* There is a gradual rise up to 45ºC
* There is a steep fall after 45ºC
I can conclude from this investigation that yeast respires best a 45ºC, but further analysis of my graph shows a steep fall after this point, as I predicted (see prediction) this is a result in the enzymes becoming denatured, so the reaction stopped. My prediction also said the best temperature would be 35-37ºC but because different enzymes work at different temperatures the best temperature was slightly higher. Also because the higher the temperature the more energy particles have to move around resulting in an increase in collisions, therefore a better chemical reaction. Apart from my prediction on the best temperature my conclusion fully supports my prediction, bubbles of C02 were produced and the enzymes did denature at a high temperature resulting in the reaction eventually stopping.
Evaluation
My results were reliable, as I had no anomalies, if I had they would have been visible in my graph, I had also strictly controlled the amounts of water, sugar and yeast in my method resulting in valid data to make a reliable conclusion. To improve this investigation I could see if more sugar affected the rate of respiration, carried out more experiments with lower temperatures of water e.g. 15ºC, 10ºC, 5ºC and even 0ºC, this would give me a better graph showing me a full gradual rise up to 45ºC. I could also have used better equipment, instead of the delivery tube I could have used a burette, this would have made counting the bubbles easier making my results more accurate. I could have also had the end of it in a beaker of limewater then if it turned cloudy/ milky it would have proved that the bubbles were CO2, as this is the test for carbon dioxide. Some things that helped me do a good investigation were preliminary work I had done before the experiments. I went through the stages of setting up my equipment, what I should do and also the amounts of yeast, sugar and water I should use, and also a sensible range of water temperatures. I had also completed a computer simulation of the experiment to give me better knowledge of what I was doing.
