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Chapter 3 Practice Paper: Biological Molecules — question paper

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QQ/S3CBI/CH3

Secondary 3 · Combined Science (Biology) (G2 / G3)

Chapter 3 Practice Paper

Biological Molecules

Duration: 40 minutes
Total: 30 marks
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READ THESE INSTRUCTIONS FIRST

  • Answer all questions.
  • Section A: choose the one correct answer for each multiple-choice question.
  • Section B: answer in the spaces provided; show all necessary working.
  • Give numerical answers to 3 significant figures where appropriate, with units.
  • Biological drawings are not required; describe or label structures in words where asked.
  • The use of a calculator is permitted.

Original practice material written for the MOE Combined Science (Biology) syllabus. It is not an official MOE or school examination paper. Chapter 3 (roles of carbohydrates, fats and proteins; food tests; building units; lock-and-key enzyme action; temperature and pH effects).

For Examiner’s Use
Section A/ 10
Section B/ 20
Total/ 30

Section A: Multiple-choice questions[10 marks]

Choose the one correct answer for each question.

  1. 1

    Which reagent gives a purple colour with protein?

    1. Aiodine solution
    2. Bethanol
    3. Cbiuret solution
    4. DBenedict's solution
    ( )
  2. 2

    Fats are synthesised from which building blocks?

    1. Aglycerol and fatty acids
    2. Bglucose units
    3. Camino acids
    4. Dstarch and glycogen
    ( )
  3. 3

    An enzyme works fastest at 37 °C and not at all at 60 °C. At 60 °C the enzyme has been

    1. Adiluted
    2. Bdigested
    3. Cfrozen
    4. Ddenatured
    ( )
  4. 4

    The active site of an enzyme is

    1. Athe part broken down in digestion
    2. Bshaped to fit one specific substrate
    3. Cdestroyed after each reaction
    4. Dmade of starch
    ( )
  5. 5

    Heated Benedict's solution turns green with a drink. The drink contains

    1. Ano reducing sugar
    2. Ba low concentration of reducing sugar
    3. Ca high concentration of reducing sugar
    4. Dprotein
    ( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided.

  1. 1

    A food scientist tests an unknown sample with three reagents. Iodine gives a blue-black colour. Biuret stays blue. Shaking with ethanol and pouring into water gives a cloudy white layer.

    1. (a)

      State what each of the three results shows about the sample.

      [3]
    2. (b)

      Starch molecules are built up from one kind of small molecule. Name it.

      [1]
    3. (c)

      The scientist also heats a fresh portion with Benedict's solution and it turns brick-red. State what this shows and what the colour suggests about the amount.

      [2]
    4. (d)

      Suggest one role in the diet of the fat found in the sample.

      [2]
  2. 2

    Amylase digests starch to glucose. In an investigation, starch plus amylase was kept at different temperatures and the time for starch to disappear was recorded.

    Results

    Temperature / °CTime for starch to disappear / min
    159.0
    254.5
    352.0
    45no starch digested
    1. (a)

      Calculate the rate of digestion at 25 °C in per minute.

      rate =per minute[1]
    2. (b)

      Describe the trend shown by the results from 15 °C to 45 °C.

      [2]
    3. (c)

      Explain both parts of the trend using enzyme ideas.

      [3]
  3. 3

    A patient recovering from surgery is given a high-protein diet, and their plasma is checked for glucose after meals.

    1. (a)

      Explain why extra protein helps the patient)s recovery.

      [2]
    2. (b)

      Name the carbohydrate)s building unit whose blood level rises after a starchy meal.

      [1]
    3. (c)

      Describe how glucose in a plasma sample could be shown to be a reducing sugar, stating the result expected.

      [3]

— End of paper —