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Cambridge IGCSE Biology practice

Paper 6 structured question: Osmosis

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Osmosis

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An investigation is conducted to observe osmosis using dialysis tubing filled with sugar solutions of varying concentrations placed in distilled water. The change in mass of the tubing bags is recorded after 30 minutes.

Results Table

Results of Osmosis Investigation

The table shows the change in mass of dialysis tubing bags containing different sugar concentrations after 30 minutes in distilled water.

Sugar concentration (%)Change in mass (g)
0+0.5
10+0.3
200
30-0.2
  1. a

    Explain why the bag with 0% sugar concentration gained mass.

    Aim for approximately 2 distinct marking points.

    [2]
  2. b

    Suggest one control variable that should be kept constant during this investigation and explain why.

    Aim for approximately 2 distinct marking points.

    [2]

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Paper 6 structured question: Osmosis

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Method

Method for Osmosis Investigation

1. Cut equal lengths of dialysis tubing and soak in water to soften. 2. Tie one end of each tubing to form a bag. 3. Fill each bag with 10 cm³ of sugar solution at different concentrations (0%, 10%, 20%, 30%). 4. Tie the open end securely. 5. Blot dry and weigh each bag. 6. Place each bag in separate beakers containing 100 cm³ distilled water. 7. Leave for 30 minutes at room temperature. 8. Remove bags, blot dry, and weigh again. 9. Record the change in mass for each bag.

Sugar concentration (%)Initial mass (g)Final mass (g)Change in mass (g)
05.05.5+0.5
105.15.4+0.3
205.05.00
305.25.0-0.2
  1. a

    Identify the independent variable in this investigation.

    Aim for approximately 1 distinct marking point.

    [1]
  2. b

    Describe how you would measure the dependent variable in this investigation.

    Aim for approximately 2 distinct marking points.

    [2]