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Biology · May / June 2022 · Paper 62 · Question 1

0610

As printed in the paper

The question as text

A student investigated the effect of temperature on the diffusion of vitamin C. Vitamin C is an important part of a balanced diet and is found in some fruits and vegetables. When vegetables are boiled in water the vitamin C diffuses out into the surrounding water. A dialysis tubing bag filled with vitamin C solution was used to represent a vegetable. The blue dye DCPIP was used as an indicator for the presence of vitamin C. High concentrations of vitamin C decolourise DCPIP quickly. The student used the method described in step 1 to step 14. Step 1 A syringe was used to fill a dialysis tubing bag with 10 cm3 of vitamin C solution. Step 2 The outside of the filled dialysis tubing bag was rinsed by dipping it into a beaker of distilled water. Step 3 A large test-tube was labelled hot. The dialysis tubing bag was put into the large test-tube and secured in place with an elastic band, as shown in Fig. 1.1. Step 4 Steps 1 to 3 were repeated with a second dialysis tubing bag and a large test-tube labelled cold. large test-tube elastic band holding the open end of the dialysis tubing bag in place dialysis tubing bag containing 10 cm3 of vitamin C solution Fig. 1.1 Step 5 The large test-tube labelled hot was half-filled with hot water. Step 6 The large test-tube labelled cold was half-filled with cold water. Step 7 The temperature of the water in the large test-tube labelled hot was measured. Step 8 The temperature of the water in the large test-tube labelled cold was measured. 3 Fig. 1.2 shows the readings on the thermometer used in step 7 and step 8. 40 hot water 35 30 20 cold water 15 10 Fig. 1.2

Read automatically from the paper; the printed page above is exact.

Show the answer and mark scheme

  • 1(a)(i)[2]

    (hot water) 38.5 and (cold water) 17(.0) ;

    °C ;

  • 1(a)(ii)[1]

    (hot test-tube) 6.5 and (cold test-tube) 9(.0) ;

  • 1(a)(iii)[3]

    table drawn with a minimum of two columns and header line ; headings including units ;

    data recorded as 3.5 and 1(.0) and hot / cold or stated

    temperatures ;

  • 1(a)(iv)[1]

    any one from:

    (vitamin C) diffuses, more / faster, at high(er) temperature / in hot water ;

    greater volume of / greater amount of / more, DCPIP used, at high(er) temperature / in hot water ;

  • 1(a)(v)[1]

    to remove vitamin (C) (from the outside of the bag) / idea that rinsing prevents contamination (by vitamin C) ;

  • 1(a)(vi)[2]

    error: volume was not measured ;

    equipment: use a syringe / measuring cylinder / burette

    / graduated pipette ;

    OR

    error: temperature was not controlled ;

    equipment: use a thermostatically controlled water-bath ;

  • 1(a)(vii)[3]

    independent variable: temperature ;

    dependent variable: volume of DCPIP ;

  • 1(b)[6]

    independent variable:

    1 at least two concentrations of sugar solution ;

    dependent variable:

    2 (measuring) mass / volume, before and mass / volume, after or change in, mass / volume (of dialysis tubing or test-tube) ; 3/4/5 variables kept constant, max. three from:

    volume of water (in dialysis tubing / test-tube)
    volume of sugar solution (in dialysis tubing

    / test-tube)

    temperature
    (soaking) time
    type of dialysis tubing / surface area of tubing
    type of sugar

    6/7/8 method, max three from description of how to:

    make sugar solution, concentrations / dilutions
    maintain the temperature (during the investigation)
    make a model cell e.g., knotting dialysis tubing at both ends / other methods of securing dialysis tubing at both ends
    remove excess liquid from the tubing (if mass measured)
    measure, mass / volume / height, of water / sugar solution e.g., use of a balance / measuring cylinder / syringe / ruler 9 repeat the whole investigation at least twice more (three trials) ;
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