Practical 1 Biology [FINAL]

8/3/2019 Practical 1 Biology [FINAL]

http://slidepdf.com/reader/full/practical-1-biology-final 1/3

Effect of pH on the enzyme catalase

Thet Win HSC Bio Page 1

Aim:

To investigate the effect of pH on the activity of the enzyme catalase which is present in the

liver.

Equipment list:

40 ml of hydrogen peroxide (H2O2)

1 mol L-1 hydrochloric acid in

dropper bottle

1 mol L-1 sodium hydroxide in

dropper bottle

2 mol L-1 hydrochloric acid in

dropper bottle

2 mol L-1 sodium hydroxide in

dropper bottle

Liver

Distilled water

6 test tubes

Cutting board

Safety gloves (latex) and glasses

Electronic balance

Stop watch

Scalpel

10ml measuring cylinder

Universal indicator and pH strips

Safety risks:

Hydrochloric acid, sodium hydroxide and hydrogen peroxide are corrosive to skin and

can cause burns and serious damage if spilt into eyes. To avoid this wear safety glasses.

The liver may have some disease germs that can get inside the body and cause illness.

Wear safety gloves and wash your hands after the practical to avoid this.

The scalpel is very sharp and it can cut through skin so be cautious when using it.

Variables:

Independent- the pH concentration

Dependent- the activity of the enzyme (catalase)

Controlled variable- the hydrogen peroxide ml in each test tube

Control- Test tube 1

Method:

1. Using a measuring cylinder measure 5ml of hydrogen peroxide and pour it into each of

the six test tubes which are labelled 1-6.

2. Do not add any chemicals to test tube 1 and label this as the control.

3.

Using a pH strip and a pH chart determine the pH of the solution in test tube 1.4. Add 5 drops of hydrochloric acid into test tube 2 and then 8 drops into test tube 3.

5. Add 10 drops of distilled water into test tube 4 and then 5 drops of 1mol L -1 sodium

hydroxide into test tube 5 and 5 drops of 2mol L -1 of sodium hydroxide into test tube 6.

6. Using universal indicator strips and the pH chart determine and record the pH of

solution in each test tube from 1-6.

7. Place all test tubes in a water bath and maintain the temperature at 37oC.

8. Wear safety gloves and safety glasses to avoid touching an acid or alkali.

9. Using a scalpel, cutting board and electronic balance measure and cut six pieces of liver

of mass 3g each.

10. Carefully add one piece of liver into test tube 1 and using a stopwatch measure the timetaken by oxygen gas bubbles to reach the top of the test tube.





11. Record the time taken using an appropriate method.

12. Repeat steps 10-11 using the solution in test tubes 2-6.

13. Using a thermometer record the temperature at which the reaction occurred.

14. Repeat the experiment 10 times.

Results/observations:

Test tube Chemicals intest tube

pH Temperature(oC)

Time takenby gas to

reach the

top (s)

TRIAL 1

Time takenby gas to

reach the

top (s)

TRIAL 2

Averagetime taken

(s)

1 Hydrogen

peroxideONLY

4.5 37 12 18 15

2 1 mol L-1

hydrochloricacid +hydrogen

peroxide

2 37 105 95 100

3 2 mol L-1

hydrochloric

acid +

hydrogenperoxide

3 37 135 165 150

4 Distilledwater +

hydrogen

peroxide

6 37 6 14 10

5 1 mol L-1

sodium

hydroxide +hydrogen

peroxide

12 37 120 80 100

6 2 mol L-1

sodium

hydroxide +

hydrogenperoxide

13 37 160 140 150





Conclusion:

The trend observed is a bell shaped curve whereby the activity of the enzyme is greatest around

a pH of 6-7. This is because the enzyme catalase is found in the liver inside the human body and

it requires a neutral i.e. a pH of 7 for optimal metabolic efficiency and function. The

experimental test tubes were also placed in a water bath with a maintained temperature of 37oC

to ensure similar conditions as to what are found inside the body.

This experiment was valid for a number of reasons. One such was that the aim was

appropriately tested. Also the particular results obtained were useful information as it justified

the activity of enzymes at different pH concentrations. In terms of reliability it was quite reliable

as the results were reproduced consistently and the mean was taken.

The reaction which occurred was the decomposition of hydrogen peroxide into hydrogen and

oxygen with the catalase enzyme.

2H2O2(aq) 2H2O(l) + 02(g)

Essentially pH concentration lower or higher than 6/7 results in a slower rate of reaction as the

enzymes don’t work as efficiently. At higher temperatures they die i.e. become denatured and

can no longer function.

Documents

Practical 1 Biology [FINAL]