In this experiment I will be investigating the effect of temperature on the enzyme catalyse in yeast. I will find the optimum temperature of the catalyse when its breaking down the hydrogen peroxide onto water and oxygen.

Enzymes

Introduction

Theory

All living thing have enzymes in them, the enzymes act as catalysts; they speed up chemical reactions. The way they do this is firstly the enzyme fits perfectly round the substrate; this is called the lock and key theory. The enzyme then joins up with another enzyme that has a substrate in it and the substrates then join together to perform a chemical reaction. The enzymes also break down chemical bonds in the same way. In the case of a human body it does this most effectively at 37.5°C, this is called this the optimum temperature.

If the enzyme is in an environment with a low temperature there is less kinetic energy and the kinetic theory tells us, as things get colder they move slower and collide less frequently, this will cause the chemical reaction to slow. As the temperature increases the enzymes atoms inside start to vibrate, the kinetic theory also tells us that as atoms get hotter they move more. So if the enzyme’s molecules vibrate more the enzyme will change shape and so the substrate isn’t going to fit perfectly into it properly, this is shown below.

At this point the enzyme still works but not as efficiently as it would at the optimum temperature. If the enzyme is heated up anymore it will denature and become useless. It will be useless because of the ‘lock and key theory’, the enzyme wont fit the substrate and this means all chemical reactions will have to work without the enzymes that act as a catalyst, this means the chemical reactions become very slow or even stop. If this happened in a human the human would die because chemical reactions needed for everyday life wouldn’t be able to take place e.g. respiration. This is shown below.

Prediction

I think the yeast will work best at 37.5°C, as this is body temperature, if the temperature is higher than this then the enzyme will start to denature which causes is to not work effectively. If the temperature is lower the kinetic theory states the substrate (molecule) will move slower and the rate of reaction will slow. The graph is curved because I think the reaction will less efficient below and above the optimum temperature.

In this experiment doubling the temperature will not double the rate of reaction, this is because the enzyme has an ...

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Prediction

In this experiment doubling the temperature will not double the rate of reaction, this is because the enzyme has an optimum temperature at which it works best at. The reaction doesn’t forever increase as the temperature does.

Preliminary Work

I will do an experiment that gives an approximate idea of the optimum temperature, in this experiment I will use the temperatures 20°C 30°C, 40°C, 50°C, 60°C and 70°C this will make it easier to find the optimum temperature in the actual experiment. It will also let me test my method and see how reliable and accurate it is.

This shows the optimum temperature is around 30°C and 40°C, I chose my temperatures for my actual experiment, they are 34°C, 36°C, 38°C, 40°C and 42°C, to find the optimum temperature.

Precise

To make my experiment precise I will use the finest measurements I can which is cm3, I will be measuring the amount of oxygen produced in the reaction.

Apparatus

20ml of hydrogen peroxide, 10ml of yeast solution, water bath, conical flask, measuring cylinder, stopwatch, rubber tube, tray and rubber stopper with a hole.

Method

Set apparatus up as above.
Set water bath to the right temperature.
Measure 20ml of hydrogen peroxide solution.
Measure 10ml of yeast solution.
Put both solutions in the water bath for 10 minutes
Fill measuring cylinder with water and make sure there are not air bubbles in it, stand it upright in the tray, which also has water in it.
After 10 minutes mix the solutions put the solutions in the conical flask stir twice and put rubber stopper on it.
Start the timer as soon as solutions are stirred and measure how much oxygen is given off after 60 seconds.
Repeat the experiment twice more.

Fair Test

To ensure my test is fair I will I will only change one thing at a time; the temperature. The amount of yeast and hydrogen peroxide solution will stay the same.

Accurate

To make sure my experiment is accurate I will repeat the experiment three times at each temperature and take an average to eliminate any possible errors.

Number and Range

I am going to use 34°C 36°C 38°C 40°C and 42°C, I have chosen these small range of temperatures because I want to find the optimum temperature and my preliminary results tell me the optimum temperature is around 40°C.

Safety

To make this experiment safe I will use a water bath not a Bunsen burner, I will make sure the hydrogen peroxide doesn’t come in contact with my skin or eyes, to do this I will wear goggles and wash my skin if I should come in contact with it.

Results

Conclusion

I have found that around 38°C is the optimum temperature for the enzyme catalyse in yeast. As the temperature rises above the optimum temperature the rate of reaction slows down, the same happens as the temperature falls, I gained this information from my graph.

My results support my prediction, I predicted the catalyse would work best at 37.5°C, as this is the temperature of a human body. I also predicted the graph would curve downwards before and after the optimum temperature due to the enzymes not working efficiently. This is because if the temperature is too high the particles that make the enzyme heat up and vibrate; this causes the enzyme to change shape and therefore following ‘the lock and key theory’ the reaction can’t take place or is too slow. Also when the temperature is lower than the optimum, the kinetic theory tells us the colder the atoms the slower their particles move, this causes the atoms to move slowly and collide less often which causes the rate of reaction to slow. My prediction graph and results graph match, therefore my results match the theory and my prediction.

Evaluation

My experiment was a good way of obtaining the evidence I needed because it was a fair test, I also made sure it was accurate and precise. It allows me to find the optimum temperature.

I think my results are accurate because I did each experiment three times and took an average of all three. I had no odd results, this shows that the way I did my experiment was good at obtaining useful information because my method worked and it proved my theory and prediction correct. My results are reliable; you can tell this if you look at my table you can see the results are very similar. For instance the results for 42°C after 603 seconds are 453, 463 and 443; this proves my method is reliable.

The evidence I have obtained is good enough to support my conclusion because I found the optimum temperature, my preliminary work helped me with this, I found the number and range that enabled me to find the optimum temperature accurately and reliably.

To extend my findings I could use more yeast or hydrogen peroxide in the experiment or I could have a stronger solution of either of the two. I could also use an enzyme other than catalyse such as lipase or protease, to see whether I get the same shaped curve.

I have thought of several different way of measuring the oxygen that is produced by the reaction, I could count the amount of bubbles given off by the reaction but this could be slightly inaccurate because the bubble sizes could differ. Another way I could measure the oxygen by putting a syringe and measuring the amount of gas produced in mm3. I could also try to find the exact optimum temperature by doing a more narrow range. E.g. 37°C 37.5°C and 28°C to find the precise optimum temperature.

Jon Cade Page of