Find out if different concentrations of catalase (in this case yeast suspension) change the rate of reaction.

Seb Jenner 10A

Catalase Investigation

The aim of this investigation is to find out if different concentrations of catalase (in this case yeast suspension) change the rate of reaction. We are using yeast suspension as the catalase because it is very easy to use and it is the most reactive out of the ones that we tested.

Enzymes are made up of protein molecules, they are also catalysts, this means that they speed up biological reactions. Each type of enzyme can only speed up one kind of reaction, this is because each enzyme’s active site is a different shape and so it can only speed up the reaction of the molecule with the complementary shape. (AQA GCSE Science)

Catalase is found in every cell, it is needed because hydrogen peroxide is poisonous, the catalase reacts with it to divide it into water and oxygen.

This is a diagram of catalase:

Catalase increases the reaction rate of the decomposition of Hydrogen Peroxide into water and oxygen. This equation shows this:

Catalase

Hydrogen Peroxide---------------------->Water + Oxygen

Catalase

2H2O2 ------------------->2H2O+O2

This is a diagram showing how substrates fit together with enzymes into the active site (borrowed from John Grantham)

In order for a the breakdown of Hydrogen Peroxide to occur the molecules must collide with each other with a certain amount of energy, the more often they collide the quicker the rate of breakdown. By increasing the temperature you increase the kinetic energy, meaning that the molecules move more rapidly, therefore the rate of breakdown will be quicker. When the temperature gets to 43°C the enzymes start to denature, therefore changing the shape of their active site, meaning that they can no longer react with other molecules. By 100°C all the enzymes will have been destroyed, this is irreversible. This graph shows how the rate of breakdown would change when the temperature is increased (Encarta):

Variables

Temperature

Increasing the temperature will increase the rate of the reaction up to a point, this is because kinetic energy will be increased meaning that the enzyme molecules will move around more and collide with a greater force with the complementary substrate molecule.

Concentration of Hydrogen Peroxide

The higher the concentration of the Hydrogen Peroxide the quicker the rate of the reaction, this is because there are more substrate molecules so more collisions with catalase molecules that result in more Oxygen being produced.

Concentration of Yeast Solution (catalase)

The higher the concentration of the Yeast ...

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Variables

Temperature

Concentration of Hydrogen Peroxide

Concentration of Yeast Solution (catalase)

The higher the concentration of the Yeast Solution the quicker the rate of the reaction, this is because there are more catalase molecules and so more collisions, therefore the Hydrogen Peroxide molecules can be broken down faster too Oxygen and water.

Surface area of catalase

The greater the surface area of the catalase the more molecules are exposed, which means that there will be more collisions with Hydrogen Peroxide so Oxygen is produced faster.

I chose the concentration of yeast as my variable because it is the simplest variable to measure, and because it is simple to alter.

Apparatus

1 boiling tube
1 measuring cylinder
1 delivery tube
2 syringes (1cm3)
1 beaker
yeast solution (5 %)
hydrogen peroxide (10%)
Bung
Needle

My preliminary experiment showed me that I should use 1cm3 of yeast and 1cm of hydrogen peroxide, this was because they were very reactive and also because if I used more than 1cm3too much oxygen would be displaced. It also showed me that yeast solution was the best catalase to use because it produced the most froth, meaning it had a higher reaction rate. The preliminary experiment also gave me a chance to get accustomed to the equipment that I would be using in our investigation.

I plan on recording the increase in oxygen by recording the decrease in water in the measuring cylinder. I will record my results every five seconds up to thirty seconds.

Method

Put 1cm3 of hydrogen peroxide in test tube.
Put the bung (attached to the delivery tube) on the test tube.
Place the delivery tube in a beaker of water.
Place a measuring cylinder filled with water over the delivery tube.
Put 1cm3 of 5% yeast in to the test tube (using syringe).
Record the volume of Oxygen, over a period of 20 seconds, in the measuring cylinder (subtract 1cm3 of displaced gas).
Repeat method, decreasing concentration of yeast (catalase) by 1% each time.

To insure that I make my experiment safe and fair, I will attempt to keep all the variables (except the concentration of yeast) the same. Hydrogen peroxide is an irritant, so I will wear safety goggles at all times, I will also stand whilst doing the experiment, and keeping loose items of clothing, tucked in so as to prevent an accident.

Prediction

I predict that the greater the concentration of the yeast the faster the reaction rate and therefore the greater the volume of oxygen produced in the 20 seconds that I have allocated. This is because catalase increases the breakdown rate of hydrogen peroxide and the greater the concentration of catalase the more molecules of catalase there will be and the more collisions meaning more breakdowns in the thirty seconds.

In order to alter the concentration of the yeast solution, I will dilute it with water. This is shown below

Tube yeast solution cm3 water cm3 Concentration of yeast

1 1 0 20%

2 0.8 0.2 18%

3 0.6 0.4 16%

4 0.4 0.6 14%

5 0.2 0.8 12%

6 0 1 10%

Results

These results are 1ml short of what we actually got because when we put in the 1ml of yeast it displaces 1ml of gas.

Average:

The Graph on the next page and the results above show that the greater the concentration of catalase, the more oxygen is produced in a shorter space of time. This is because there are more catalase molecules and so more collisions, therefore the Hydrogen Peroxide molecules can be broken down faster too Oxygen and water. One thing that I would have expected to see was a limit in the speed that the reaction occurred with the different concentrations. I obviously should have continued my experiment to achieve these results.

I believe that my results were fairly accurate, however to improve them I could have repeated the experiment, and continued for more than 20 seconds. A problem that I could not overcome was the reliability of the human eye. I may have misread the volume on the measuring cylinder, however without expensive machinery I could not achieve perfection.

Bibliography:

∙ Encarta 99 - enzymes

∙ AQA GCSE Science pages 20 to 23

∙ www.bbc.co.uk/schools/gcsebitesize/biology/humans/enzymes