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IGCSEBiology
Trial Class

Original practice · 5 questions · 17 marks · about 19 minutes

Osmosis and Water Potential Practice Questions

Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.

These original Cambridge-style questions test the wording and application that students most often lose marks on. They are not official Cambridge questions and do not reproduce any past paper.

Before you open the answers

  • Attempt every question without notes.
  • Show working for calculations and write complete biological statements.
  • Use the suggested time as a guide, not a strict limit on the first attempt.

These are original practice questions. They do not reproduce an official Cambridge paper or official mark scheme.

  1. Question 1

    Paper 4 Extended 3 marks Difficulty 2/5

    Define osmosis using the terms required for an Extended answer.

    Show model answer and marking guidance
    1. Net movement of water molecules.
    2. From a region of higher water potential to a region of lower water potential.
    3. Through a partially permeable membrane.

    Model answer

    Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

    Watch for: Describing the movement of solute, or omitting the membrane.

  2. Question 2

    Paper 4 Both 4 marks Difficulty 3/5

    A plant cell is placed in a concentrated sugar solution. Describe and explain what happens to the cell.

    Show model answer and marking guidance
    1. Water moves out of the cell.
    2. Movement occurs by osmosis through the partially permeable cell membrane.
    3. Outside solution has lower water potential than the cell sap, credited at Extended level.
    4. The cell becomes flaccid and may become plasmolysed as the membrane pulls away from the wall.

    Watch for: Saying the cell wall pulls away; it is the cell membrane and contents.

  3. Question 3

    Paper 5/6 Both 3 marks Difficulty 2/5

    A potato cylinder has an initial mass of 5.20 g and a final mass of 4.55 g. Calculate the percentage change in mass.

    Show model answer and marking guidance
    1. Change = 4.55 − 5.20 = −0.65 g.
    2. Percentage change = −0.65 ÷ 5.20 × 100.
    3. Answer = −12.5%.

    Watch for: Dividing by the final mass instead of the initial mass.

  4. Question 4

    Paper 5/6 Both 4 marks Difficulty 3/5

    State four variables that should be controlled when comparing mass change of potato cylinders in different sugar concentrations.

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    1. Initial length or diameter/surface area of the cylinders.
    2. Source or type of potato tissue.
    3. Volume of solution.
    4. Time left in solution or temperature, with any four specific relevant controls credited.

    Watch for: Listing sugar concentration, which is the independent variable.

  5. Question 5

    Paper 5/6 Extended 3 marks Difficulty 4/5

    A graph of mean percentage mass change crosses zero at 0.42 mol dm⁻³. Explain what this indicates.

    Show model answer and marking guidance
    1. There is no net movement of water at this concentration.
    2. The solution and potato tissue have approximately equal water potential.
    3. 0.42 mol dm⁻³ estimates the internal solute concentration or isotonic point of the tissue.

    Watch for: Saying osmosis has stopped completely; water still moves both ways with no net movement.

Mark the set consistently

Award a point only when the idea is clearly present in the written answer. Correct any missed point in a complete sentence, then test the same skill on a different question several days later.

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