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5090/31

Biology 5090/31 — October/November 2022

Cambridge O-Level · Practical Test · worked solutions for every part, with the mark scheme

3
questions
40
marks
75
minutes

Topics Experimental Contexts · Planning Experiments and Investigations · Analysis, Conclusions and Evaluation · Observations and Measurements · Microscopy and Biological Drawing

Q119MExperimental ContextsPlanning Experiments and InvestigationsObservations and MeasurementsAnalysis, Conclusions and EvaluationFree sample

Foods can be tested to determine the types of molecules that they contain.

You are going to investigate the composition of two foods, A and B.

You are provided with the reagents for three different tests.

For the first test:

  • label a test-tube A1
  • place food A on a tile and cut a cube 1 cm×1 cm×1 cm1\,\text{cm} \times 1\,\text{cm} \times 1\,\text{cm} from it
  • carefully cut this cube into three parts, all the same size
  • take one of these three parts, cut it into small pieces and put the small pieces into test-tube A1
  • pour 2 cm32\,\text{cm}^3 of ethanol into test-tube A1
  • place a stopper in the top of the test-tube and shake the test-tube well
  • remove the stopper and place the test-tube in a rack
  • carefully clean your cutting equipment
  • label a test-tube B1
  • repeat the process above using food B, taking care to cut one piece into a similar number of small pieces as for food A.

Allow the solid contents to settle to the bottom of both test-tubes, which should take no more than ten minutes. Continue with the question while the solid contents settle.

For the second test:

  • label one test-tube A2 and another test-tube B2
  • cut the second part of cube A into small pieces and put the small pieces into test-tube A2
  • pour 2 cm32\,\text{cm}^3 of distilled water into test-tube A2
  • use a glass rod to stir the contents of test-tube A2
  • clean the glass rod and your cutting equipment
  • repeat the steps above using the second part of cube B and test-tube B2
  • add 2 cm32\,\text{cm}^3 of biuret reagent to each of test-tubes A2 and B2.
  • stir the contents of test-tubes A2 and B2 for one minute, cleaning the glass rod after stirring A2
  • place the test-tubes in a rack to allow the solid contents to settle.

Return to test-tubes A1 and B1. Continue with the following instructions for test-tubes A1, B1 and the remaining two empty test-tubes:

  • label one empty test-tube A1W and another empty test-tube B1W
  • add 3 cm33\,\text{cm}^3 of distilled water to each of the test-tubes A1W and B1W
  • take test-tube A1 and carefully pour the liquid from the top of the mixture into test-tube A1W
  • take test-tube B1 and carefully pour the liquid from the top of the mixture into test-tube B1W.

For the third test:

  • on a tile, add iodine solution to the third pieces of food A and food B.
(a)
(i)

Explain why it was necessary to clean your cutting equipment after cutting food A.

______

1M
(ii)

Suggest why you were asked to cut A and B into a similar number of small pieces.

______

1M
(b)
(i)

Observe the appearance of the solutions in test-tubes A1W, B1W, A2, B2 and the foods A and B tested with iodine solution. Record your observations in the table.

test reagentobservations food Aobservations food B
ethanol
biuret reagent
iodine solution
7M
(ii)

Using the information in the table, state what you can conclude about the composition of A and B.

test with ethanol ______

test with biuret reagent ______

test with iodine solution ______

6M
(c)

State two possible sources of error in these tests that may have affected the results.

For each source of error suggest how it could be overcome.

  1. source of error = ______
    suggestion = ______
  2. source of error = ______
    suggestion = ______
4M

The rest of this paper

2 more questions
  • Q2Microscopy and Biological Drawing · Experimental Contexts10M
  • Q3Analysis, Conclusions and Evaluation · Experimental Contexts · Planning Experiments and Investigations11M
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