Apparatus:
- 5 test tubes
- 5 beakers
- Yeast balls
- Glucose water (10%)
- Kettle
- Pipette
- Spatula
Diagram:
Variables:
The input variable we used was temperature as we used different temperatures between 20°c and 60°c.
The output variable was the time it took for a yeast ball to rise. The controlled variables were the concentration of glucose, the PH, the amount of yeast balls and the amount of glucose.
We will keep the concentration of glucose constant by only using 10%. We will use an equal number of yeast balls (8) for each test tube and we will use 25cm³ of glucose for each test tube.
Prediction:
I predict that the yeast balls will rise fastest at a temperature of 30°c or 40°c as the optimum temperature for glucose is about 37°c. It is 37°c because this is body temperature. I expect that the temperatures below 30°c will take a very long time to make a yeast ball rise or none will rise at all, as there is not enough energy and because of the collision theory. Similarly, if the temperature is too high the yeast ball will take a long time to rise or not rise at all because the enzyme will denature.
Number:
We will repeat the experiment twice for each different temperature so that our results are more reliable. Our average is then likely to be more accurate than just using our first try.
Range:
We will wait up to 20 minutes for the yeast balls to rise. If none rise in the 20 minutes I will assume there is no reaction. The temperatures we are using are between 20°c and 60°c.
Scientific Knowledge:
If the temperature is too low there will not be enough energy for a reaction to take place because of the collision theory. If the temperature is too high the enzymes will denature and the reaction will not occur. To work properly the temperature needs to be close to the optimum temperature of the enzyme. This is usually body temperature that is 37°c.
Method (with changes):
After doing preliminary work we decided to do the experiment slightly differently to the way we first planned. We prepared 5 test tubes with 4 yeast balls in each. We decided to change the amount of yeast balls because on our first try of using 8 yeast balls nothing happened even at 40°c.
We added the 5 test tubes to water baths of temperatures 20°c, 30°c, 40°c, 50°c and 60°c. We then times how long it took for one yeast ball to rise and noted the time down. We then repeated the experiment for each different temperature so we could get a more reliable average.
Results
Table showing results including averages and rate.
All times in seconds
Analysis
The results show that at 20°c there was no reaction as no yeast balls rose after doing the experiment twice. This would mean that at 20°c there was not enough energy for a reaction to take place. In all of the other experiments at higher temperatures up to 60°c yeast balls did rise. At 30°c the average time was 750 seconds, which was the longest time of all the temperatures where yeast balls rose. This shows that at 30°c there was still not much energy from the heat of the water bath. At 40°c, which in my prediction I thought would be the optimum temperature, the reaction was faster at a rate of 0.002 and with an average time of 490 seconds. It was however 3rd fastest out of 5 so immediately it is obvious that my prediction was not correct. 50°c was the temperature at which the reaction was fastest with the highest rate and the least time. It took 378 seconds till a yeast ball rose. This shows that glucose works best around the temperature of 50°c. At 60°c the reaction was almost as fast as at 50°c taking just 386 seconds for a yeast ball to rise. From the results of the experiment at 40°c, 50°c and 60°c we can work out that the optimum temperature is between 50°c and 60°c. This is because 60°c is only just slower than at 50°c but at 40°c it is a lot slower.
This graph shows how temperature affects the time taken for a reaction to take place. This graph shows us that the reaction was fastest at 50°c and slowest at 30°c. The reaction time started to increase again at 60°c so the reactions peak is at 50°c.
The graph shows how temperature affects the rate of respiration. The higher the temperature got the faster the rate of respiration. It shows that the rate peaked at 50°c and then started to drop at 60°c. 20°c was not included on the graph because no reaction took place at this temperature.
Evaluation
The experiments results differed from what I had predicted. From my results there were no anomalies so my results should have been very accurate. They are accurate because the results for each of the different temperatures are similar and it is unlikely that it went wrong all 3 times. This means that my prediction was wrong.
I predicted that the enzyme would work best at body temperature, which is between 30°c and 40°c but my experiment proved that the enzyme works best at close to 50°c. The optimum temperature for fermentation is about 50°c.
If I were to do this experiment again I would maybe use a higher concentration of glucose because this would mean that the reactions would happen faster and there would be a faster rate. Doing this would mean that I would be able to repeat the experiment for the same time a couple more times and I would therefore be able to get a more accurate average. If I were to do the experiment again I would also time how long it takes for all of the yeast balls to rise because this would mean a larger difference in rates/times between the different temperatures.
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