Investigating the effect of the substrate concentration on the decomposition of Hydrogen Peroxide by the enzyme catalase.

* Ph level can also affect enzymes in the same way raising the temperature can. There is a range in which a catalase will work well in when the ph range is changed this affects the number of free hydrogen or hydroxyl ions. This affects the charge on the amino acid residues which make up the enzyme which leads to denaturation. This again changes the shapes of the sites therefore stopping the substrate particles being able to slot in to be broken down.

* Substrate concentration also affects rate of the reaction. As the concentration increases there are more particles which will collide with each other. As there can be more collision between the particles and enzymes there are more chances for successful collisions to occur where catalases can break down hydrogen peroxide.

* Surface area can also affect how quick the reaction is this is as the particles will have a greater area for collisions to occur therefore more successful reactions can take place.

* Enzyme concentration will also affect the rate of the reaction. The higher the concentration of enzymes the more there will be to break down the hydrogen peroxide. This means H202 will be broken down much quicker making the rate of the reaction increase.

Variables

The variables I will control are:

) PH

2) Enzyme concentration

3) Surface area of liver

4) Temperature

The variable that I will change for my investigation is the substrate concentration of hydrogen peroxide.

I will measure the amount of oxygen produced in a set amount of time to make a fair test.

Preliminary work

I used FOCUS software to do some experiments before I actually done my practical. I knew this would help me with my experiment as it would tell me how I could improve my practical. The focus software let me test temperature and enzyme concentration on the enzyme amylase. I found out that if I put the temperature over 37 degrees the enzyme will stop working properly therefore I knew I would keep my experiment at room temperature as enzymes will still work on it. Also I found out that the higher the enzyme concentration got the quicker the rate of the reaction occurred.

Also this software helped me pick my variables and make me do a fair test.

I also done this test with potatoes but I had insufficient results. I think I had bad results as potatoes do not contain much catalase inside there cells so therefore decided to use liver instead. As you can see below here are the results for the bad experiment.

Concentration

0%

0%

5%

20%

Apparatus

Apparatus

Reason why used

Conical flask

Can use bung on it so gas does not escape.

Bung

Blocks air escaping has pipe on it so that gas will only go to where directed e.g. to gas syringe.

Balance top

Very precise at weighing even the lightest objects.

Clamp

Securely can hold gas syringe in place.

Gas syringe

This can efficiently read the amount of gas produced

Scalpel and tweezers

To hold and cut the liver

Delivery tube

To carry oxygen to the gas syringe.

Liver

As it contains high amounts of catalase to break down the hydrogen peroxide.

Hydrogen Peroxide

The substrate in different concentrations as the variable of my experiment.

Stop watch

To time how long my experiment will go on which will be 60 seconds each time.

Diagram

Method

) Set up apparatus( should look similar to above except without liver or hydrogen peroxide yet)

2) Weigh 1g of mashed up liver on a top pan balance and then put the liver into the conical flask.

3) Cautiously measure out 50ml of hydrogen peroxide at 0% concentration in a measuring cylinder.

4) Pour this into the conical flask and securely seal the bung immediately within 2 seconds so that gas cannot escape and start the stop watch straight away.

5) Now gently swirl the conical flask at 60 seconds take the reading of the amount of oxygen that has collected in the gas syringe

6) Clean out the conical flask thoroughly and repeat experiment with 5, 10, 15 and 20% concentrations of Hydrogen peroxide.

7) Repeat each concentration 3 times so that you acquire more accurate results.

8) Calculate the average of each concentration and make graphs.

9) Then from your results work out the rate of each reaction.

Safety

You have to take many safety precautions when dealing which chemicals such as hydrogen peroxide. It is an irritant and can irritate parts such as eyes and skin. Hydrogen Peroxide is a strong oxidising agent even though it is not flammable; it can react with something such as iron and can help support combustion immensely as it is releasing oxygen. In science labs you should always read the labels for example hydrogen peroxide should have the irritant logo on and the oxidising logo.

To help safety in when the experiment takes place some safety precautions must take place below I will state some:

* Wear safety goggles this will prevent chances of hydrogen peroxide getting to your eyes.

* Wear gloves this will prevent chance of hydrogen peroxide getting onto your skin. Therefore there is a less chance of skin irritation.

* Tie hair back if it is long this stops your hair getting in the way. Also as it is out of the way it is better if there is a spillage less chance anything splashes onto your hair.

In case of an accident and you come in contact with hydrogen peroxide below are some precautions you must take:

* If hydrogen peroxide comes in contact with your skin it will temporarily bleach it in a whitish colour. You should immediately wash contacted area with plenty of water. If not done properly you can be left with red blisters.

* If Hydrogen peroxide comes into contact with your eyes you can get severe pain that later goes away. You should wash your eyes out with cold water. If a high concentration of hydrogen peroxide comes into your eye you should consult doctors or physician immediately as it can damage the cornea.

* If you inhale Hydrogen peroxide you will get irritation of nose and throat, which should later subside if it was a low concentration. If it was a high concentration this can cause irritation to lungs or even poisoning therefore you should consult a doctor.

Fair Testing

Variable

How I plan to control variable

Temperature

All the experiments will be carried out at room temperature. I will measure the temperature of each flask at the start to make sure they are around about the same. I will not redo this at the end as the reaction will create heat and raise the temperature anyway.

Enzyme concentration

I will only use 1g of liver for each experiment as this will make sure that there is a accurate amount of catalase in each experiment.

Surface are of liver

I will mash up the liver completely so that it will remove aspects of surface area from my experiment.

The amount of gas lost

The amount of gas lost should be under 2 seconds as I try to seal flask with bung immediately.

The amount of swirling

I will swirl the conical flask at a consistent rate throughout the experiment.

Accuracy

To make my experiment accurate as possible I will try and do a range of things. I will need to do my experiment accurately so that I can obtain correct results. The precautions I will take to do my experiment accurate are:

* Keep all my experiments at room temperature. To do this I will measure the temperature of the room before I start each experiment.

* Use a measuring cylinder to measure out 50ml of Hydrogen peroxide so that I get an even amount in each experiment.

* Use a digital balance top to weigh the liver these are very good weighing devices and will give me precise weight of each liver piece.

* When I start my experiment close bung as quickly as possible and firmly so gas does not escape.

* Use a stop watch to exactly time 60 seconds for each experiment.

* Use a calculator to work out the average rate so I get precise answers.

Prediction

I predict that the higher the concentration of the substrate will be the quicker the break down of Hydrogen peroxide will be. I think this because when the concentration of hydrogen peroxide increases the amount of molecules in the substrate increases therefore more can collide increasing the chance of a successful collision occurring. Therefore if I double the concentration I predict that the substrate will be broken down twice as quick.

I think the enzymes will work at a consistent rate as the test will take place at room temperature. This is because the hydrogen peroxide molecules will have more energy and will cause more collisions with the enzymes. As a result of this enzymes will be breaking down the hydrogen peroxide into water and oxygen quicker. If the temperature increases too much for example over 50 degrees Celsius the active sites on the enzymes will change and become denatured. This will make the break down of hydrogen peroxide stop and will give me bad results.

I also presume that when the concentration gets to high there will be a point where the enzymes will be working as fast as they can all active sites will be occupied at all times and as of this they will not be able to work any faster this means enzymes will reach there Vmax( maximum rate of a enzyme).

I think my results should make a sloping graph to a point where it will not rise anymore. This is because of factors like enzymes reaching there Vmax.

I predict my results will show a positive correlation as higher the concentration the faster the rate of the reaction as more oxygen will be produced.

Results

Gas produced after 1 minute (cm³)

Concentration (%)

Test 1

Test 2

Test 3

0%

0

0

0

5%

4

3

5

0%

21

26

32

5%

68

85

91

20%

71

82

84

Concentration

Average Gas produced after 1 minute(cm³)

0%

0.0

5%

4.0

0%

26.3

5%

81.3

20%

79.0

Concentration

Average rate of reaction (cm³/s)

0%

0.0

5%

0.06

0%

0.44

5%

.355

20%

.316

Rate= Average Volume of Gas

Time Taken

Biology Coursework Page 1