A student places a thin slice of fresh potato into a beaker of concentrated salt solution. After 30 minutes, the student notices that the potato slice has become soft and flexible. Explain why the potato slice became soft and flexible.

Cambridge International IGCSE Biology (0610) — 3.1 Diffusion · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Water moves out of the potato cells by osmosis.
Water moves from the potato cells (higher water concentration) to the salt solution (lower water concentration) down the concentration gradient.
The potato cells lose water and become flaccid.
Turgor pressure is reduced or lost, so the cells no longer push against the cell wall, making the tissue soft and flexible.

Examiner tips

  • Use the word ‘osmosis’ to show understanding of the process. Explain the direction of water movement in terms of concentration gradients. Mention loss of turgor pressure as the reason for softness. Keep each point concise to fit the 4‑mark structure.

Common mistakes

  • Confusing diffusion with osmosis. Failing to mention the concentration gradient. Over‑explaining the cell wall mechanics or using vague terms like ‘pressure’ without specifying turgor.

Mark scheme (4 marks)

  1. Water moves out of the potato cells by osmosis
  2. Water moves from the potato cells (higher water concentration / less concentrated) to the salt solution (lower water concentration / more concentrated), down the concentration gradient
  3. The potato cells lose water and the cells become flaccid
  4. Turgor pressure is reduced / lost, so the cells no longer push against the cell wall, causing the tissue to become soft and flexible

Related

More Diffusion questions

▶ Try answering this question with AI marking (free) →