List of Apparatus
Measuring cylinder
Yeast mixture (yeast, plain flour, sugar)
Stirring Rod
10 ml water
Water bath or water at the correct temperature
Diagram
Method
- Measure out 10g of plain flour, 0,5g of sugar, 1.0g of yeast and 20cm cubed of water.
- Carefully mix together the flour, sugar, and yeast.
- Pour this mixture into a beaker and slowly add the water, a little at a time, whilst stirring thoroughly in between.
- Stir the mixture with the glass rod till all lumps are gone and the mixture is consistently smooth.
- Pour the mixture back into the measuring cylinder. Take care that none sticks to the side.
- Record the level of the mixture on the measuring cylinder.
- Place the cylinder somewhere at the appropriate temperature.
- Record the level of the temperature at regular intervals e.g. 10 mins
- Record results in a table of results.
- Repeat the same temperature 3 times.
- Repeat these steps again with the different temperatures.
Fair Testing
- Make sure that all the ingredients are measured out accurately.
- The final solution is to be kept at the chosen temperature constantly.
- Make sure that no solution is lost whilst pouring from beaker to measuring cylinder.
- Make sure all apparatus is clean before use.
- Use plain flour not self-rising.
Safety
In this experiment we used the standard lab safety procedure. We had to be careful with the glass beakers, as glass, unlike plastic, is breakable. We also had to be careful with the water, as some of the temperatures needed in the experiment would scold us.
Table of Results
Conclusion
After repeating my pilot experiment with a wider range of temperatures I have found that at 50°C the enzymes are nearest their optimum heat capacity and caused the dough to rise the most. It rose due to the enzymes anaerobically respiring. At 50°C the yeast rose by 99.0 cm³. This was because the enzymes in the yeast had more kinetic energy at this temperature. In my hypothesis I predicted, with the help of my pilot results, that the higher the temperature, the more carbon dioxide will be produced until it reaches a certain temperature. Using my scientific knowledge, I know that most enzymes are denatured at 100°C. I predicted that maximum carbon dioxide would be produced at the highest temperature I used which was 70°C. My results prove this was not so as by viewing the graph I can tell that at 60°C the carbon dioxide produced was 28 centimetres cubed. This is due to the fact that the enzymes had already begun to denature. I could do more temperatures between the ranges of 40-60° increasing in 2°C. These would be 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C and 60°C. This would pinpoint the exact optimum heat capacity for the enzymes.
In my experiment I used the formula:
Enzymes
Glucose → Carbon Dioxide + Ethanol + Energy
The sugar supplied the glucose, which the enzymes in the yeast converted into carbon dioxide, ethanol and energy. The carbon dioxide bubbles got trapped in the yeast solution raising the level of the mixture.
My graph supports my hypothesis as it is a bell shape. This shows that at first as the temperature rose so did the volume of the yeast. The yeast was increasing due to increased enzyme activity. At 50°C it shows the enzymes activity to be at its greatest giving me the impression that this is the optimum heat capacity of the enzyme. After this the graph shows that activity falls meaning the enzyme has become denatured and will no longer fit its substrate.
Evaluation
After doing each temperature 3 times and finding the average I feel I have enough results and I am happy with them. The experiment was easy to set up, use and it was moderately easy to take the measurements. I am happy with the level of accuracy of my results as there is not much I could improve in the way I did the experiment that would greatly improve my results. I feel I have a few anomalous results with the 50°C cylinder. After 15 minutes one of my three cylinders had a reading of 44 cm³ whilst another one had a reading of 68 cm³. This is the biggest difference between any of the results and I feel that with a difference of 22cm³ I feel that something must have gone wrong with the cylinder that I took the lowest readings off. With high insight I feel that the temperature of this cylinder was probably not maintained at 50°C. I could now redo the three cylinders for 50°C but I do not feel that it would change my overall results. The recordings could have been slightly inaccurate as it was fairly difficult to take the readings off the measuring cylinders. I feel that repeating each temperature three times and taking the average was an appropriate level of accuracy for the experiment in hand.
Although the experiment was fairly easy to do I did come across some difficulties. It is quite hard pouring the solution into the measuring cylinder without getting any stuck to the sides. Also maintaining the correct temperature all the way through the experiment was fairly tricky. From the graph we can see that the enzymes begin to denature at 50°C. I expected the graph to have a more rounded bell shape appearance. From here I could repeat the experiment with more precise temperatures between 40-60° in 2° intervals. This would help me to find the precise optimum heat capacity of the enzymes. Also if I wanted more accurate results of the temperatures used in this experiment, I could repeat everything but do each temperature five times instead of three. This would give an even more precise average. There are many factors that could affect my investigation such as the temperature the yeast respires at as at different temperatures the enzymes in yeast work faster or slower at breaking down the glucose. The amount of yeast will also have an effect on the results; as if we are to use different amounts in each experiment it will form an unfair test. Another factor that could affect our investigation is the percentage of glucose in the yeast. I overcame this by ensuring that an equal amount of glucose in each mixture. I must also make sure to leave all experiments undisturbed during the course of respiring; this means they cannot be stirred. Due to all these factors the results will not be 100% reliable. There will always have to be room for error due to human error.
I feel that the results are enough to support my conclusion as all what I had predicted to come true has done. Although I did have a couple of anomalous results with the 50°C it did not affect my overall results. The results I obtained were not that reliable, as the equipment I was working with was not very advanced. We could not keep the cylinders at the precise temperatures all the time, as we did not have the equipment available to do so. Also the readings could be very slightly out as the mixture forms a meniscus on the cylinders, but I took this into consideration as I took the readings so I believe the readings in themselves are accurate.
Overall I think that my experiment proved my hypothesis correct and I am pleased with my results.
