Investigation into how changing the potato catalase enzyme concentration affects the rate of reaction.

Rate

Amount enzyme

If you double the concentration of potato catalyse then the rate should double as well because there are twice as many molecules of enzyme catalyst available that can get hydrogen peroxide substrate molecules attached to there active site. This is because molecules are constantly moving and bumping into on another. When a substrate molecule bumps into an enzyme molecule that is right, it fits into a depression on the surface called the active site. The chance of molecules hitting an enzyme molecule at the right angle is twice as lightly. So the more movement the twice as likely it is to hit an enzyme molecule. At a certain enzyme concentration the reaction will stay the same because all the active sites will have been used up leaving none free for any hydrogen peroxide molecules so they will have to wait for an active site to become available. This is shown by the reaction staying the same, hence the line staying horizontal, on the above graph

All the way thorough the experiment I am not going to change the concentration on hydrogen peroxide, because that will alter the amount of substrate molecules likely to hit an active site.

Preliminary experiment plan

        I will do experiments with 1cm cylinders of potato and add one at a time keeping record of how many 1cm pieces I am adding. I will find the highest and lowest amount of pieces I can go up or down to and still get a readable result.

        I will also test out some of the different concentrations to see which gives the easiest result to read from.

Preliminary experiment results

From my preliminary’s I can see that I need to use 2 moles concentration because any less and the result is not readable and any more and there is too much gas produced. And the lowest amount of pieces I can use is 1, 1cm piece and the highest with still getting a readable amount is ten 1cm pieces. I am going to use five readings ranging from two 1cm pieces to ten 1cm pieces going up in two’s. I am going to use 20ml of hydrogen peroxide so there is enough to stay active all through the experiment, and so that there is enough to keep all the potato pieces submerged under the hydrogen peroxide. I have not controlled PH and temperature meaning I have not got a result as accurate as it could be. I have controlled the substrate mole amount because if I hadn’t then the result I get might be because of the increased or decreased substrate molecule amount instead of the varying enzyme concentration.

This is a plan of the table I will use to record my results.

Risk assessment

• Hydrogen peroxide is very corrosive, all spills on the skin need to be rinsed under cold water, and any spills on the bench need to be wiped up.
• Goggles must be worn if you do not wear glasses.
• If water is spilt on the floor it must be wiped up to save injuries.

Table of results

Procedure

List of apparatus:

• 3 Test tubes/boiling tubes, (one extra just encase needed)
• Delivery tube (that fits tightly to the test tube/boiling tube)
• Water bath
• 300cm3 of 2mole Hydrogen peroxide
• 90 1cm pieces of Potato cylinders
• Knife
• Slate to cut on
• Ruler
• 10cm3 Syringe
• Stop clock

Instructions

Before you start make sure the bung fits tightly into the test tube/boiling tube, so that gas does not escape, you can keep using this one all the way through and washing it out in between experiments, or you can use different ones if they all fit the bung snugly.

1. Get out all equipment and chemicals as shown above, and set them up as shown in the diagram at the beginning. If the potato is not cut up do so now, they need to be very accurately cut to 1cm pieces and continue using the same ruler throughout.

2. Place 20ml of hydrogen into the test tube. Put two pieces of potato, into the test tube with the hydrogen peroxide put the bung in and start the timer. Time for a minute keeping watch of how much gas is being produced.

3. After a minute record how much oxygen has been released, on the table. Wash out the test tube or get a new one, and repeat steps 1 and 2, two more time.

4. Repeat steps 1-3 using 4 pieces of potato, then 6, then 8 and then 10 pieces.

If too much gas is produced you can switch very quickly to another test tube and keep on timing.

Table of results

        

Analysing and considering my evidence

Trends

My graph shows that the amount of oxygen released increased at a steady rate up until eight 1cm Pieces of potato, at which the amount of oxygen released still increased but at a slower rate. I conclude from these trends that potato catalase enzyme affects the rate of reaction but the reaction starts to increase at a slower rate at about eight 1cm pieces. This is because at eight 1cm pieces all the enzyme active sites are in use so the substrate molecules have to wait for one to become available. Up until this point the rate increases as more substrate molecules are released causing more collisions meaning more substrate molecules can fit into the enzyme molecules active site causing more reactions and more oxygen can be produced.

These results match my prediction because from two 1cm pieces to eight 1cm pieces the rate increases at a steady rate, but at eight 1cm pieces and ten 1cm pieces the rate starts increasing at a slower rate.

        My doubling theory has not been proven on this experiment because at two 1cm pieces of potato I had 2.8 cm3 and at four 1cm pieces the amount of oxygen released is 4.2cm3. This is a lot less than double, but at four 1cm pieces there was 4.2cm3 of oxygen released and at eight 1cm pieces there was 9cm3 of oxygen released which is more than doubled so my results do not follow my doubling prediction.

Evaluating your evidence

I think my results came out as expected but my doubling theory did not come out as expected it did not match the prediction, I think I carried out a fair test though because I used very accurate equipment. I did not get any anomalous results my results increased at a steady rate until a certain point the line is straight so I don’t think any of my results were anomalous.

 I think my procedure was accurate but if I had a device for cutting the potato cylinders to exactly the same length then it would be even more accurate. I think my results are accurate. I used the most accurate clock and measuring cylinder I could find in the department to measure my results, but if I had looked outside of the school equipment I could have got more accurately measured test tubes, and stop clock.

I can be sure that my results are reliable because I did all my experiments three times on each amount of potato enzyme. I think I do have enough evidence for my conclusion because I can conclude that my doubling theory did not work but that the more 1cm pieces of potato I added the more oxygen was released up to a certain concentration where it still increased but at a slower rate.