Aim

“To see what factors affect the decomposition of hydrogen peroxide by the enzyme catalase which is found in the liver”

Introduction

Enzymes are biological catalysts. They speed up the chemical reactions which go on inside living things. Without them the reactions would be so slow that life would grind to a halt.

Enzymes work by when a substrate molecule bumps into a molecule of the right enzyme; it fits into a depression on the surface of the enzyme molecule.

This depression is called the active site. The reaction then takes place and the molecules of product leave the active site, freeing it for another substrate molecule.

Hydrogen peroxide is a waste product produced during respiration. Hydrogen peroxide is produced to kill off dangerous bacteria.

The hydrogen peroxide is broken down, so that it cannot be dangerous anymore, into water (which is given off when you perspire) and into oxygen (which can be given off when you exhale).

A toxin like hydrogen peroxide must be broken down because if it is kept in the body for too long it can react with cell walls and damage them or break them down.

The variables that affect the decomposition of hydrogen peroxide are:

1. The temperature of the liver

2. The surface area of the liver

3. The pH of the hydrogen peroxide

4. The concentration of the enzymes

The two variables I am going to look at are temperature and surface area.

Hypothesis

I think that when we test the surface area the bigger the surface area the quicker the reaction will be. This is because there are more liver particles that will be exposed to the hydrogen peroxide,

therefore the liver that is ground up will be the quickest reaction.

For temperature it will be the temperature that is forty degrees Celsius because the enzymes in the liver will not exist after the temperature goes over forty degrees Celsius. I know this due to previous experiments that I have carried out.

I think the rate of decomposition will double every ten degrees Celsius that the liver is warmed up, but when the liver goes over forty degrees Celsius, the rate of decomposition will slow down.

Therefore my hypothesis is that the rate of decomposition will be at its fastest with a temperature of forty degrees Celsius and a surface area of grinded liver.

Apparatus

Trough, bung, water, burette, hydrogen peroxide, liver

(1.4g), test tube (with delivery tube), beaker, Bunsen burner, thermometer, tripod, gauze, clamp and boss, stand.

Method

1. Set up the apparatus as in the diagram.

2. Put 1.4g of liver in a test tube with delivery tube. Add sand to all experiments to have a fair test with the liver that is ground up (sand separates the liver easily).

3. Add 10cm’ of hydrogen peroxide to the liver. Replace the bung quickly so that no gas is lost.

4. After 10 seconds record the amount of water displaced in the burette. Record this amount on a table.

5. Repeat steps 1-4 heating the liver to 30’C, 40’C and 50’C.

6. Repeat steps 1-5 with liver weighting 1.4g cut in half, into quarters and ground up.

7. Remember to wear goggles and use all the safety procedures.