Animal Transport

• Investigation to find the effect of pH on the activity of the enzyme rennin

  1. Step 1: Label 3 test-tubes P, Q, R

  2. Step 2: Add 5 cm3 of milk to each test-tube

  3. Step 3: Add 2 drops of acid to test-tube P

  4. Step 4: Add 2 drops of distilled water to test-tube Q

  5. Step 5: Add 2 drops of alkali to test-tube R

  6. Step 6: Label 3 more test-tubes P1, Q1, R1

  7. Step 7: Add 1 cm3 of 0.1% rennin solution to each of P1, Q1, R1

  8. Step 8: Place all 6 test-tubes in 40°C water bath for 3 minutes

  9. Step 9: Add contents of P1 to P, Q1 to Q, R1 to R

  10. Step 10: Start stopwatch, keep P, Q, R in water bath

  11. Step 11: After 1 minute, remove P, tilt and rotate, observe clotting stage
• Rennin


  Enzyme that changes the protein in milk so it can be digested by another enzyme
• Rennin action


  Causes small lumps or clots to form in milk
• Young mammals feed on milk containing protein
• Rennin changes the protein in milk so it can be digested by another enzyme
• The action of rennin causes small lumps or clots to form in the milk
• Step 4


  A dropping pipette was used to add two drops of distilled water to test-tube Q
• Step 5


  A dropping pipette was used to add two drops of alkali to test-tube R
• Step 6


  Another three test-tubes were labelled P1, Q1 and R1
• Step 7


  A clean syringe was used to add 1 cm3 of 0.1% rennin solution to each of test-tubes P1, Q1 and R1
• Step 8


  All six test-tubes were placed into a water-bath at 40 °C and left for three minutes
• Step 9


  1. The contents of test-tube P1 were added to test-tube P

  2. The contents of test-tube Q1 were added to test-tube Q

  3. The contents of test-tube R1 were added to test-tube R
• Step 10


  Test-tubes P, Q and R were kept in the water-bath and a stop-clock was started
• Step 11


  1. After one minute, test-tube P was removed from the water-bath

  2. It was tipped and rotated as shown in Fig. 1.1

  3. The appearance of the milk was observed, and the stage of clotting was decided by comparing it to the diagrams in Fig. 1.1
• Step 12


  Test-tube P was returned to the water-bath
• Step 13


  Steps 11 and 12 were repeated for test-tubes Q and R
• Step 14


  Steps 11, 12 and 13 were repeated every minute for five minutes
• Test-tube P had some clotting at one minute and was all clotted at two minutes
• Test-tube Q had no clotting at one, two or three minutes but some clotting at four and five minutes
• Test-tube R had no clotting throughout the investigation, and remained unchanged after five minutes
• pH


  Activity of renin
• Optimum pH for the renin enzyme

  • Acidic, where it clots quickly
• Renin


  • Doesn't work at alkaline solution
  • Works slowly in water (neutral conditions)
• Rotation is not being standardised
• Subjective judgement to end point
• Drops source of error as they might not be of same size
• No repeats
• Used acids and alkalis which are irritants
• Hazards require the use of eye protection