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Biology · Oct / Nov 2024 · Paper 61 · Question 1

0610

As printed in the paper

The question as text

A student investigated the movement of water across a membrane by osmosis. Dialysis tubing is made from a type of membrane that is partially permeable. Only small molecules such as water can pass through this membrane. The student used this method: Step 1 Label two test-tubes S and W. Step 2 Put 20 cm3 of distilled water into each of the labelled test-tubes. Step 3 Take a piece of dialysis tubing and knot it at one end to form a bag. Step 4 Put 6 cm3 of sucrose solution into the open end of the dialysis tubing bag. Step 5 Rinse the outside of the dialysis tubing bag with distilled water. Step 6 Use a ruler to measure the distance from the knot at the bottom of the dialysis tubing bag to the bottom of the meniscus in the bag, as shown in Fig. 1.1. finger and thumb holding the dialysis tubing bag bottom of the meniscus distance to measure knotted end Fig. 1.1 Step 7 Place the dialysis tubing bag into test-tube S. Fold the open end of the bag over the top of the test-tube. Use an elastic band to hold the dialysis tubing in place, as shown in Fig. 1.2. 3 elastic band top of the open end of the dialysis tubing bag folded over sucrose solution dialysis tubing bag distilled water test-tube knotted end Fig. 1.2 Step 8 Repeat steps 3 to 7 using test-tube W and 6 cm3 of distilled water instead of sucrose solution in step 4. Step 9 Place both test-tubes into a hot water-bath for 15 minutes. Step 10 After 15 minutes, remove test-tubes S and W from the hot water-bath and put them into a test-tube rack. Step 11 Remove the dialysis tubing bag from test-tube S. Use the ruler to re-measure the distance from the knot at the bottom of the dialysis tubing bag to the bottom of the meniscus in the bag. Step 12 Repeat step 11 with test-tube W.

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

Show the answer and mark scheme

  • 1(a)(i)[3]

    table drawn with minimum of three columns and a header line ;

    suitable headings for (test-)tube and distance with units in mm or cm ;

    recording of four correct measurements (for both S and W, each at 0 minutes and 15 minutes) ;

  • 1(a)(ii)[1]

    correct calculation from candidate’s results for S and W ;

  • 1(a)(iii)[1]

    water has moved into, bag S / the sucrose solution ;

  • 1(b)(i)[1]

    measuring cylinder / AVP ;

  • 1(b)(ii)[1]

    to remove any sucrose solution (from the outside of the dialysis tubing bag) ;

  • 1(b)(iii)[1]

    to ensure that it was the sucrose that was causing the effect / AW ;

  • 1(b)(iv)[2]

    any two from:

    volume of water in the test-tubes ;

    volume of liquid in the tubing bag / AW ;

    time (dialysis tubing bags left in, test-tubes / the water-bath) ;

    temperature (of the water-bath) ;

    type of dialysis, tubing / bag ;

    where the measurements were taken from ;

  • 1(b)(v)[1]

    to identify anomalous results / AW ;

  • 1(b)(vi)[1]

    any one from:

    measure the height of the liquid in the test-tube (at the start and end) ; measure the volume (inside the bag / in the test tube) ;

    measure the, mass of the liquid in bag / water in the test-tube) ;

  • 1(c)[2]

    add Benedict’s (solution / reagent) ;

    heat ;

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