Name: Judy Sim Kim LaiClass: 4A

TitleStudying the effects of pH on the activity of pepsin

Problem statementWhat are the effects of pH on the activity of pepsin?

ObjectiveTo study the effects of pH on the activity of pepsin

HypothesisAn acidic medium of pH3 is optimum for the activity of pepsin.

VariablesManipulated: pH of mediumResponding: Rate of reaction catalysed by pepsinFixed: Volume and concentration of albumen suspension, volume and concentration of pepsin

solution and temperature of medium

MaterialsAlbumen suspension, 1% pepsin, 0.1M hydrochloric acid, 0.1M sodium hydroxide solution and distilled water

ApparatusBeakers, droppers, thermometers, test tubes, 5ml syringes, pH paper, a wire gauze, a Bunsen burner, a tripod, a stopwatch and a test-tube rack

Technique usedObserve the condition of mixtures at the beginning of experiment and after 20minutes and record the changes of mixtures.

Procedures

judy/bio/peka/4A/2010

1ml of 0.1M hydrochloric acid + 1ml of 1% pepsin solution

1ml of distilled water + 1ml of 1% pepsin solution

1ml of 0.1M sodium hydroxide + 1ml of 1% pepsin solution

1. Prepare an albumen suspension by mixing egg white with 500ml of distilled water. Boil the suspension and leave it to cool. Discharge large particles using glass wool.

2. Label three test tubes P, Q and R.3. Put 5ml of albumen suspension into each test tube using a syringe.4. Add the following solutions into each test tube:

P - 1ml of 0.1M hydrochloric acid + 1ml of 1% pepsin solutionQ - 1ml of distilled water + 1ml of 1% pepsin solution R- 1ml of 0.1M sodium hydroxide + 1ml of 1% pepsin solution

5. Dip a piece of pH paper into each test tube and record the pH value.6. Immerse all the test tubes in the water bath where the temperature is maintained at 37℃ for

20minutes.7. Observe the conditions of the mixtures at the beginning of the experiment and again after

minutes.8. Record the results in a table.

Results

Test tube pHMixtures

Beginning of the experiment

After 20 minutes

P 3 cloudy clearQ 7 cloudy cloudyR 8 cloudy cloudy

Discussion1. The test tubes need to be immersed in the water bath with the temperature maintained at 37℃

because this is the optimum temperature for the action of pepsin.2. From the results, the cloudy albumen suspension becomes clear when the pH value is 3 in acidic

condition while the albumen remains cloudy in neutral and alkaline condition.3. In acidic condition (pH3), the actionof pepsin on albumen is active because the optimum pH for

activity of pepsin is 3.4. In alkaline and neutral condition (pH7 and 8), the action of pepsin on albumen is unactive

because the optimum pH for activity of pepsin is 3.

ConclusionAn acidic medium of pH3 is optimum for the activity of pepsin.So, the hypothesis is accepted.

judy/bio/peka/4A/2010