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Biology · May / June 2022 · Paper 61 · Question 1

0610

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The question as text

Rice contains starch. Amylase is an enzyme that catalyses the breakdown of starch to form reducing sugars. A student investigated the effect of amylase on cooked rice. The student used this method: Step 1 Two small beakers were prepared; each beaker contained 20 g of cooked white rice. One beaker was labelled W and one beaker was labelled A. Step 2 Both of the beakers were put into a 40 °C water-bath. Step 3 A measuring cylinder was used to add 20 cm3 of distilled water to the rice in beaker W. Step 4 The same measuring cylinder was then used to add 20 cm3 of a 1% amylase solution to the rice in beaker A. Step 5 The beakers were left in the water-bath for 10 minutes. Step 6 One test-tube was labelled W10 and a second test-tube was labelled A10. Step 7 After 10 minutes, a glass rod was used to stir the contents of beaker W. Step 8 A clean pipette was used to remove 2 cm3 of the liquid surrounding the rice in beaker W. The 2 cm3 of liquid was put into test-tube W10. Step 9 Steps 7 and 8 were repeated with beaker A and test-tube A10. Step 10 A syringe was used to add 2 cm3 of Benedict’s solution to each of test-tubes W10 and A10. Step 11 Test-tubes W10 and A10 were put into an 80 °C water-bath for five minutes. Step 12 After five minutes, the colours of the contents of test-tubes W10 and A10 were observed. The student’s observations are shown in Fig. 1.1. W10 – started blue and stayed blue A10 – started blue and became orange Fig. 1.1

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Show the answer and mark scheme

  • 1(a)(i)[2]

    table drawn with two, columns / rows with line separating headings from body of table and with suitable headings ;

    recording of blue / no change, in W(10) and orange in A(10) ;

  • 1(a)(ii)[1]

    rice contains starch / starch is broken down to form (reducing) sugar / starch is broken down by amylase / (reducing) sugar is produced when amylase is present ora ;

  • 1(a)(iii)[2]

    any two from:

    mass of rice ;

    type of rice ;

    temperature (of the water-bath) ;

    time (in water-bath after adding rice) ;

    volume of water and, amylase / solution / liquid, added ;

    sample size (removed) ;

    volume of Benedict’s solution (used) ;

  • 1(a)(iv)[1]

    as a control (investigation) / for comparison / to show what would happen if no amylase were present / to show the (colour) change was due to amylase / AW ;

  • 1(a)(v)[1]

    any one from:

    W(10), will change colour / turn, yellow / green / orange / red ;

    a positive result in (test-tube) W(10) ;

    (reducing) sugar present in (test-tube) W(10) ;

    both test-tubes show a positive result with Benedict’s solution ;

  • 1(a)(vi)[1]

    any one from:

    thermostatically controlled water-bath ;

    thermo-isolated container / insulated jacket / (foam) insulation / AW ;

    lid (used on water bath) ;

  • 1(b)[2]

    (test rice with) iodine (solution / reagent) / iodine in potassium iodide solution ; (observe) blue-black colour (if starch present) ;

  • 1(c)(i)[2]

    (the activity of amylase / mass of (reducing) sugar produced), increased and then decreased (as the temperature increased) ;

    peak / optimum / AW, temperature is 35 °C ± 1 °C ;

  • 1(c)(ii)[2]

    6 (mg per minute) ;;

  • 1(c)(iii)[2]

    test at smaller intervals of temperature ;

    select a narrower range of temperatures around 35 °C ;

  • 1(d)[6]

    either – reducing sugar method

    1

    independent variable:

    at least two pH values tested / two pH values stated ;

    2

    dependent variable:

    time to (first) colour change / colour of Benedict’s solution after a set period of time (at 80 °C) of time / mass, of (reducing) sugars ;

    3,4 variables kept constant, max. two from ;;

    volume of pH solution
    concentration of amylase (solution)
    volume / quantity, of amylase (solution)
    type of amylase solution
    temperature
    volume of starch suspension / mass of (starch source) / AW
    concentration of starch suspension (if used)
    source of starch suspension
    volume of Benedict’s (solution)

    5, 6 given method, max. two from ;;

    take (fixed volume of) samples
    (testing with) Benedict’s (solution)
    heat / incubate at 80 °C

    7, 8 new method, max. two from ;;

    use of buffer
    use of colorimeter (for Benedict’s) / colour chart
    use of balance to measure mass (of reducing sugars / precipitate) 9

    repeat investigation twice / at least two replicates ;

    10 relevant safety precaution: gloves / goggles / tongs / test-tube holder ; 11 AVP ; e. g., equilibration time (in the water bath before mixing)

    OR disappearance of starch method

    (cont./…)

    independent variable:

    1

    at least two pH values tested / two pH values stated ;

    dependent variable:

    2

    time for iodine solution to stay yellow-brown / disappearance of starch ; 3, 4 variables kept constant, max. two from ;;

    volume of pH solution
    concentration of amylase
    volume / quantity, of amylase solution
    type of amylase solution
    temperature
    volume of starch suspension / mass of rice / mass of plant tissue / AW
    concentration of starch suspension (if used)
    same source of starch

    5, 6 given method

    take (fixed volume of) samples ;

    samples taken at regular intervals ;

    7, 8 new method, max. two from ;;

    use of buffer
    (testing with), iodine solution
    use of spotting / white, tile

    9

    repeat investigation twice / at least two replicates ;

    10 relevant safety precaution: gloves / goggles ;

    11

    AVP ; e.g. equilibration time (in the water bath before mixing)

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