Enzymes are biological catalysts they can speed up or slow down chemical reactions but they do not get used up they are produced by living cells. Enzymes are made up of proteins. There are three main enzyme groups:
- Carbohydrases these turn carbohydrates into simple sugars.
- Lipases turn fats in to fatty acids and glycerol.
- Proteases turn proteins into amino acids.
All enzymes have an optimal working temperature, which differs according to where the enzymes are going to work for example enzymes in the body work best at 36° as this is the bodies normal working temperature.
Each enzyme has its own specific substance to digest meaning that only certain enzymes can aid the digestion of certain foods, in this case yeast and glucose.
The way that an enzyme recognises what it can digest is through an active site, which is like a lock and the key which fits into this lock is the substrate of that enzyme e.g. lipase’s substrate is fat. This process is called the lock and key theory.
Respiration = glucose + oxygen = carbon dioxide + water
Anerobic respiration = glucose + oxygen = carbon dioxide + alcohol
Prediction / hypothesis.
From the knowledge gained from research and background information it is possible to say that yeast have an optimal working temperature as it is an enzyme. it is also possible to say that if yeast work at a too high temperature then they denature this is when the enzymes cease to work properly, they do not die as they were never alive in the first place. This is what may happen to the yeast in the experiment.
Apparatus
- Test tubes
- Yeast solution
- Test tube rack
- Thermometer
- Bunsen burner
- Beaker
- Tripod
- Wire gauze
- Rubber stopper and glass tube
- sealed off top of syringe
- syringe
- Stop watch
- Large basin
- water bath
Method
Set up the apparatus as shown in the diagram, but do not attach the rubber stopper and glass tube until the yeast is at the right temperature. For each experiment you need to wait for 1 minute before you record the volume of carbon dioxide produced. Start with the coldest temperature so that even if the yeast hardly respires it will not de-nature, you must use all 5 temperatures eventually: 20, 30, 40, 50, 60. When you have sorted this out and the yeast is at the right temperature attach the rubber stopper and glass tubing, have 3 test tubes filled with yeast from the same batch as you need to repeat each temperature 3 times so as to be able to take an average.
You must mix the glucose and yeast ½ an hour before starting the experiment to allow the yeast to start respiring.
Practical techniques to avoid inaccuracies.
Each temperature was done three times to obtain an average. The test tubes were filled using a syringe to the same volume (10cm³). The same batch of yeast was used throughout the experiment so it as always at the same glucose concentration. The temperature of the yeast was measured to find the temperature not the water around it. The size of test tube was kept the same throughout the experiment in case a larger test tube heated quicker and altered the yeast. When taking readings from the thermometer we waited for it to settle and then took the reading as accurately as possible and did no round up or down and just left it as it was. Readings from the blocked off syringe were taken to the nearest whole number as more precise readings could not be taken using the equipment available the readings were also taken when the syringe was vertical so as to try to create more accurate results.
Safety considerations.
As the most of the equipment is glass you have to be careful not to drop it, by holding it carefully, not waving it around. If you accidentally drop a piece of glass equipment and it breaks then you have to clear up the glass as it is a danger to others. If a thermometer breaks then as well as glass you have the liquid inside. Which is normally mercury a poisonous substance. You also must not eat the yeast as it might harm your health. When you are heating you must be careful not to burn your self on the Bunsen burner, tripod, wire gauze or the glass. When carrying out the experiment you must also ware a lab coat and safety glasses.
Preliminary work.
Some preliminary work was needed to find out the range of temperatures needed.
I had to find the highest and lowest suitable temperatures for the experiment so I could work out the range.
These were the results of my preliminary work:
80°c - 0cm³ of gas produced too high temperature
70°c - 0cm³ of gas produced too high temperature
60°c - 0.5cm³ of gas produced
10°c – 0.5cm³ of gas produced
20°c - 1.5cm³ of gas produced
From these results I decided to use the temperatures:
20°c
30°c
40°c
50°c
60°c
Results
The yeast was left for 1 minute each time.
A 10% glucose concentration was used with the yeast all the time.
Analysis
From studying the table of results it is possible to see that 2 results that may have gone wrong, as they are dissimilar to the other two results. These results are my first result for 20°c, which is 4cm³ when the others are 2 cm³, and my second result for 40°c, which is 1 cm³ when the others are 4 cm³.
The graph shows that as the temperature of the yeast increases, so does the production of carbon dioxide. In this experiment, you can see that the production of yeast increased as the temperature rose, from 20°c producing 2.67 cm³ to 40°c producing3.33 cm³. As you can see from the graph as well as the evidence provided as the temperature rose in this experiment so did the production of carbon dioxide. In this experiment this occurred up to a point, which in this case was 40°c after this time as you can see from the graph the production of carbon dioxide went down. The production went down from 3.33 cm³ at 40°c to 1.00 cm³ at 60°c. This pattern occurs because around 40°c is the yeast’s optimum working temperature, this is one of the reasons that our body is kept at a constant temperature, so the enzymes can work efficiently. On either side of this the yeast work less and less efficiently. on the cooler side the yeast just continues to work, but a lot slower, but on the hot side as the temperature increases the yeast firstly start to work slower and then at around 70°c as show in my preliminary work they stop working and even when cooled down still cease to work. When yeast do this they become what is called denatured, which is almost like they have died except that they cannot die as they were never alive.
The graph and results do support my hypothesis as I said that either side of a peak the enzymes will work less and less efficiently. In my hypothesis I did not say that the enzymes would denature, this occurs when the temperature gets too hot for the enzymes to work and as the enzymes were never alive they cannot die so they denature.
Evaluation
The results apart from the two errors are similar to the others at the same temperature and this combined with an average give more accurate results not meaning that they are correct though.
From looking at the table my results seem quite accurate as the temperatures increase evenly the averages increase quiet evenly as well and also the use of an average increases accuracy by if there is one wrong result reducing its affect. From the graph my results seem accurate as well as they are all close to the line of best fit indicating accuracy.
The method did work because it produced a set of results that showed that my hypothesis was right and when placed into the form of a graph gave correlation and with a line of best fit gives reliable results.
From the data gathered I could give the conclusion that out of the 5 temperatures 40°c is the best or most efficient temperature for the enzymes in the yeast to work at.
The inaccuracies in this experiment came from the use of the equipment. The thermometer as some readings were in between two temperatures and the collection of the gas in the syringe end was inaccurate as the scale on the syringe did not go down to a small enough reading so approximations had to be made.
To increase the accuracy in this experiment more accurate apparatus could have been used, an electric thermometer and a more precise device for measuring the gas
To improve this method you need to collect gas for a longer period of time on each one e.g. half an hour. You could also use a larger amount of temperatures e.g. 0c, 5c, 10c, 15c, 20c… up to a higher temperature than before e.g. 10 0°c.
