Fair test
I have chosen to investigate the effect of temperature change on the respiration rate of yeast, so I must keep the other variable factors the same to make the test a fair test, so that my results can be considered accurate and reliable. This is a list of the factors I must keep the same and how I will keep them analogous.
Amount of glucose, I will keep this factor the same by measuring how much sugar I put in the test tube with the yeast.
Amount of oxygen, this will be kept constant because the air in the room will be the air in the test tube, which means that all the experiments, which will all be performed in the same room, will have the same amount of oxygen.
Equipment used, this will be very easy to control, all I have to do is make sure I set out my experiment each time as it is in the diagram.
Amount of yeast, once again, this is easily controlled by simply measuring the yeast in the test tube.
Amount of water, just like the sugar and the yeast, this will be easily controlled by measuring the amount of water I add to the test tube.
Method
I will set up the experiment as shown in the diagram, then I will use 3g of sugar, 3g of yeast and 10ml of water in the test tube for each experiment. These are the variable factors I will need to keep the same,
Amount of glucose,
Amount of oxygen,
Amount of Sugar,
Amount of yeast,
Amount of water,
The equipment I use.
I will do 7 experiments at 30°,35°,40°,45°,50°,55° and 60° to determine which temperature yeast respires the quickest at, and when the enzymes de-nature.
Safety Precautions
I will wear safety goggles to prevent anything getting into and damaging or irritating my eyes, and i will conduct myself in a calm and sensible manner at times to prevent injury.
Ensuring Reliability
I will repeat my experiment to ensure that my results are reliable. I will use the average of the two results to plot my graph.
Analyzing
From my investigation, I have discovered that just as I predicted, the temperature affects the rate of yeast respiration. The yeast respired more quickly at higher temperatures, but if the temperature becomes too high, the enzymes essential for respiration in yeast become denatured, and this causes the organism ( in this case the yeast) to die. This is illustrated in the graph on the previous page. As you can see, the amount of carbon dioxide produced rises greatly between 30 and 40 degrees centigrade, but after 40 degrees C, the enzymes in the yeast become denatured. The graph shows this clearly, after 40 degrees, the line of best fit falls which shows that the amount of CO2 produced decreases severely, until it almost stops completely, this means respiration has stopped because respiring yeast produces CO2. This is because, the higher the temperature, the higher the energy level of the enzymes and substrate molecules or ‘enzyme substrate complexes’ (see research page 9). The more kinetic energy they have, the more they collide and the more reactions take place between them. The enzyme becomes denatured because the weak chemical bonds which hold the molecule in the specific shape for one substrate, are broken. The increase in molecular collisions and vibrations at higher temperatures, is enough to permanently change the shape of the ‘active site’ (see page 9 of research). When this occurs the enzyme is said to be denatured because it can no longer connect with the substrates to form an enzyme substrate complex as the active site, (where the substrate fits onto the enzyme) is unalterably changed.
The evidence I obtained supports the prediction I made;
‘I predict that the temperature of the yeast will affect it’s rate of respiration. I think this is because the enzymes which are essential for respiration perform differently in different temperatures. In colder temperatures yeast respires more slowly, and at ‘higher temperatures the yeast works faster’ (page 8 of my research), until about 45-50°C ‘when the enzyme molecule becomes denatured, the yeast will stop respiring, and so cause the death of the organism’ (page 8 of my research at the back of this investigation, I have highlighted the relevant parts)’.
The results were exactly as I predicted, when the temperature got higher the yeast respired more, until the heat caused the molecules to vibrate too fast, and the high temperature caused the enzymes to denature. In colder temperatures the yeast did not respire as well because in order to start the reaction, you need a small amount of ‘activation energy’ (page 9 of my research), which at cold temperatures the molecules do not have until they heat up. However, when the molecules heat up, they are not denatured by cold temperatures as they are by hot temperatures.
Evaluation
The procedure was fairly simple to perform, and the evidence I obtained was reliable. The accuracy of my experiment is of course marred by human error, meaning that my experiment is only as accurate as the person who records the results. There was only one anomalous result in my experiment, which was 17.5 cm3 of co2, produced at 60 degrees centigrade. I saw that this result was anomalous, and did not plot it on the graph. The procedure itself was reasonably suitable in that I was able to draw a firm conclusion from the results I obtained, but there were errors in it. These errors were;
1. the water in the beaker could not be consistently kept at the temperature I required, to combat this problem I would need a thermostatically controlled water bath. This would be far more reliable than a beaker full of water and a thermometer.
2. The cork kept leaking at the sides of the test tube and where the tubing went into the test tube via the cork, perhaps to stop this occurring I needed to coat the cork in some kind of waterproof material, e.g plastic, wax, or some kind of water resistant jelly.
3. The bubbles caused by the yeast respiring kept blocking the tubing, which was stopping the CO2 from collecting properly. I had to keep unblocking the experiment by hand. To stop this occurring again, It would be useful to have a larger test tube, which would stop the bubbles reaching the tubing so soon.
4. The burette was not the most reliable of all equipment suitable for this task, a gas syringe would have been far more accurate to measure the amount of CO2 produced. However the burette is far more accurate than counting bubbles of CO2 or using a measuring cylinder, which is nowhere near accurate for the accuracy required in this experiment.
If I wished to expand upon my experiment, I think it would be interesting to extend the enquiry to discover the exact point when all the yeast enzymes become denatured, and stop producing CO2 altogether. Another way to provide additional evidence for the conclusion would be to re-do the experiment, with the suggested improvements, and instead of increasing the temperature 5 degrees every time, I could increase it 1 degree at a time, and find the exact optimum temperature at which the yeast will respire more quickly at than any other temperature.
