Biology 5090/61 — May/June 2018
Cambridge O-Level · Alternative to Practical · worked solutions for every part, with the mark scheme
Topics Experimental Contexts · Analysis, Conclusions and Evaluation · Observations and Measurements · Planning Experiments and Investigations · Use of Techniques, Apparatus and Materials · Microscopy and Biological Drawing
A student investigated the digestion of protein in mammals.
He used:
- a solution of protein that is milky in appearance
- a solution of an enzyme that is found in the stomach of mammals
- a pH solution with a particular pH value
- some distilled water.
He knew that, as the protein was digested, the protein solution would turn from milky to clear.
He set up four test-tubes, A, B, C and D, and put of protein solution into each one. He then placed the four test-tubes in a water bath for 5 minutes.
After 5 minutes, he added other solutions to the 4 test-tubes so that their contents were as shown:
| A | B | C | D |
|---|---|---|---|
| protein solution | protein solution | protein solution | protein solution |
| 5 drops of distilled water | 5 drops of pH solution | 5 drops of distilled water | 5 drops of pH solution |
| distilled water | distilled water | enzyme solution | enzyme solution |
He returned the 4 test-tubes to the water bath and observed them for the next 5 minutes.
At 3 minutes, the contents of test-tube D became clear.
At 5 minutes, the contents of test-tube C became clear.
At 5 minutes, the contents of test-tubes A and B remained milky.
Use this information to complete the table, including the column heading.
| ______ / ______ | observations: A | observations: B | observations: C | observations: D |
|---|---|---|---|---|
| 0 | milky | milky | ||
| 1 | milky | milky | ||
| 2 | milky | milky | ||
| 3 | milky | milky | ||
| 4 | milky | milky | ||
| 5 | milky | milky |
Explain what the student could conclude about the digestion of protein from these results.
Suggest a suitable temperature for the water in the water bath and explain why that temperature should be used.
Suggest a suitable piece of apparatus:
for measuring the volume of enzyme solution = ______
for adding the pH solution = ______
Explain why distilled water was added to test-tubes A, B and C.
______
Giving full experimental details, design an experiment based on test-tube D to investigate the effect of different pH values on the action of this enzyme.
State and explain one safety precaution that should be taken when this experiment is carried out.
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