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AS & A Level · AS/A Level

Biology

Membranes and transport

Name: ____________________Date: October 10, 2026
  1. 1.

    Explain why oxygen can cross a phospholipid bilayer directly whereas sodium ions usually require a membrane protein.

    [3 marks] · no calculator
  2. 2.

    A plant cell is placed in a solution of lower water potential than its cytoplasm. Explain the direction of net water movement and the possible effect on the cell membrane.

    [3 marks] · no calculator
  3. 3.

    A potato cylinder increases from 2.40 g to 2.70 g in a solution; its surface is blotted consistently before both weighings. Assume mass change is due only to net water movement. Calculate percentage mass change and infer the net water movement.

    [3 marks]
  4. 4.

    Explain sodium-glucose cotransport in an intestinal epithelial cell, including the indirect role of ATP.

    [3 marks] · no calculator
  5. 5.

    Beetroot discs heated at different temperatures release pigment. Design controls that allow absorbance to be interpreted as membrane permeability rather than unequal tissue amounts or cutting damage.

    [4 marks] · no calculator
  6. 6.

    Uptake of a solute plateaus as external concentration rises and falls when respiration is inhibited. Evaluate whether this proves active transport.

    [4 marks] · no calculator

Original, unofficial practice questions from SubjectScout — not official past-paper questions.

Marking points are indicative, not an official mark scheme. Accept equivalent valid methods and supported interpretations that address the task; award each mark once without requiring the model wording.