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Enzemes Potato Hydrogen Peroxide

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How the concentration of enzymes controls the breakdown of Hydrogen Peroxide?


We are investigating the effect of changing the concentration of the enzyme catalase has on the rate of breaking down of Hydrogen Peroxide.

Background Info-

This experiment will involve some soft potato. Potato has a very high enzyme count, thatÐŽ¦s why we use it in this experiment. This enzyme is called catalase. It is used in our body to break down food and other things that we might digest. A catalase speeds up the rate of reactions. The enzymes are all protean molecules. We will also use Hydrogen Peroxide and washing up liquid. The catalase breaks down the Hydrogen Peroxide into oxygen and water. The more vigorous the reaction the more froth that it creates.

The reaction in the experiment:

Hydrogen peroxide „Ñ- oxygen + water

2H2O2 „Ñ- O2 + H2O

The enzyme can be used around the body to help chemical reactions, it speeds them up! The enzyme breaks up larger molecules into smaller pieces. This is how the enzymes work below I have described some of the things that can affect how well it works.

Fair test/ Factors-

Temp- This can affect the movement of the particles. The higher the temp the faster the particles will move and the more collisions. If the temp of the Hydrogen Peroxide is too low the experiment will fail!

High Temp- It gives them more energy so they move faster this means that they are likely to connect the substrate and the active site. The high temp also gives the particles kinetic energy. This means that the Hydrogen Peroxide will be broken down quicker.

Best Temp- This is the hottest the enzyme can be heated without the active site changing (denaturing). If the active site changes then the reaction will no longer work. From our preliminary test we found out that the optimum temp is 25oc this is around room temp.

PH- All enzymes have an optimum PH, the wrong PH can cause denaturing. The Ph canÐŽ¦t be too acid or alkaline so keep it as near to 7 as possible. If the enzyme denatures then it is no use for breaking down the Hydrogen Peroxide.

Concentration of H2O2- The higher the concentration the more collisions with the active site. This means there is an increased rate of reaction. Creating more froth so the concentration will have to be the same for each of the test tubes. The max we are going to use is 20% H2O2.

Volume of H2O2- The volume must cover the whole of the chip, otherwise the test top/ unexposed layer of the potato wouldnÐŽ¦t react with the Hydrogen Peroxide. Also the more Hydrogen Peroxide added the more likely gas given off will increase. This means that the reaction would make more froth given an unfair test.

Source of enzyme- Different potatoes will have different levels of enzymes in them. If one had more enzymes then another it may be able to breakdown the Hydrogen Peroxide quicker. We are just going to use the same potato (tesco value) for every one!

Concentration of the enzyme- VARIABLE! we can change the size of the potato chip showing more or less surface area. This is changing the concentration of the enzyme. The potato shapes will all be cuboids from 1cm x 1cm x 1cm - 1cm x 1cm x 5cm. 1cm3, 2cm3, 3cm3, 4cm3, 5cm3. The cuboids with the largest surface area has the largest concentration and vice versa.


Potato chips from 1cm x 1cm x 1cm - 1cm x 1cm x 5cm

2 Test tubes

Cutting blade (for the potatoes)


Test tube rack

Boiling tub*

Hydrogen Peroxide

Measuring cylinder

Stop clock

Washing up liquid*


Waterproof trayЎЁ

Test tube plug with thin plastic tubeЎЁ

ЎЁ only in the real test

* only in preliminary test

Preliminary test-

An experiment was carried out to find the optimum temperature for working enzymes.

1. Get the moistened potato and chop to 1cm x 1cm x 3cm

2. Start the water bath at 20oc and let it warm up

3. Pour 10cm3 Hydrogen Peroxide into a test tube

4. Get the potato and put it in an other test tube with some water

5. Put both of these test tubes in the heated boiling tank

6. Wait for about 3-5 minutes then take out the test tubes

7. Tip the potatoÐŽ¦s water in the sink and add the Hydrogen Peroxide

8. Add washing up liquid

9. Check the froth on this for every minute for 3 minutes

10. Do for all the other temperatures measured


Temp - 20oc 30oc 40oc 50oc 60oc

times Height of froth In mm (below)

60s 30 12 10 20 14

120s 35 19 15 30 17

180s 45 24 19 35 20

Optimum temp!

I have declared that a temperature between 20oc and 30oc is the optimum temperature. 30oc was too high and 20oc was too low so I have gone for around 25oc. This means the reaction will have the greatest amount of heat it can have with out denaturing the enzyme.




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