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Chapter 3 Practice Paper: Biological Molecules — question paper

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QQ/S3BI/CH3

Secondary 3 · Biology (G2 / G3)

Chapter 3 Practice Paper

Biological Molecules

Duration: 40 minutes
Total: 30 marks
Name:
Class:
Register No.:
Date:

READ THESE INSTRUCTIONS FIRST

  • Write your name, class and register number in the spaces at the top of this page.
  • Answer all questions.
  • Give numerical answers correct to 3 significant figures unless stated otherwise.
  • The number of marks is given in brackets [ ] at the end of each question or part question.
  • The total number of marks for this paper is 30.

Original practice material written for the MOE Biology syllabus. It is not an official MOE or school examination paper. Chemical elements and roles of carbohydrates, fats and proteins; food tests; synthesis of large molecules from smaller units; enzyme mode of action, specificity, and the effects of temperature and pH.

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 food test uses Benedict’s solution and a water bath?

    1. Athe test for starch
    2. Bthe test for reducing sugars
    3. Cthe test for fats
    4. Dthe test for proteins
    ( )
  2. 2

    Starch, glycogen and cellulose are all synthesised from

    1. Aamino acids
    2. Bglycerol
    3. Cfatty acids
    4. Dglucose
    ( )
  3. 3

    An amylase sample digests a starch sample in 25 seconds. The reaction rate is

    1. A25 per second
    2. B0.4 per second
    3. C0.025 per second
    4. D0.04 per second
    ( )
  4. 4

    The ‘lock and key’ hypothesis states that

    1. Aevery enzyme can bind every substrate
    2. Bsubstrates change shape to fit any active site
    3. Cthe active site and substrate have complementary shapes
    4. Denzymes are used up as each reaction ends
    ( )
  5. 5

    An enzyme is heated well above its optimum temperature. The reaction rate falls to zero because

    1. Athe substrate is destroyed by the heat
    2. Bthe enzyme’s active site is denatured and no longer fits the substrate
    3. Cthe enzyme has been used up
    4. Dwater has evaporated from the solution
    ( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided.

  1. 1

    A food scientist tests two unknown solutions, X and Y, and records the results below.

    Food test results

    TestSolution XSolution Y
    Iodine in potassium iodidestays brownstays brown
    Benedict’s (heated)brick-red precipitatestays blue
    Biuretstays blueviolet colour
    Ethanol emulsioncloudy white layerstays clear
    1. (a)

      Identify the food substances present in solution X.

      [2]
    2. (b)

      Identify the food substance present in solution Y.

      [1]
    3. (c)

      State the colour iodine solution shows when starch is present.

      [1]
    4. (d)

      Name the chemical elements present in the substance identified in (b).

      [2]
  2. 2

    The diagram (described) shows an enzyme with a notch-shaped active site and a substrate molecule that slots into it exactly.

    1. (a)

      Name the region labelled where the substrate binds, and the complex formed while the two are joined.

      [2]
    2. (b)

      Explain why this enzyme can bind only one kind of substrate.

      [2]
    3. (c)

      Explain how enzymes make reactions happen fast enough at body temperature.

      [2]
    4. (d)

      State what happens to the enzyme after the products are released.

      [1]
  3. 3

    Equal volumes of amylase and starch suspension were mixed and kept at different temperatures. The time taken for starch to disappear (iodine no longer turning blue-black) was recorded.

    Starch digestion at different temperatures

    Temperature / °CTime for starch to disappear / s
    2080
    3040
    4020
    50no starch digested in 600 s
    1. (a)

      Calculate the rate of starch digestion at 20 °C and at 40 °C, in per second.

      rates =per second[2]
    2. (b)

      Describe and explain the effect of temperature on the rate between 20 °C and 40 °C.

      [3]
    3. (c)

      Explain the result at 50 °C.

      [2]

— End of paper —