A potato chip is placed in a dilute salt solution. After 30 minutes, the chip feels firm and has increased in mass. Explain why the potato chip increased in mass.

Cambridge International IGCSE Biology (0610) — 3.2 Osmosis · 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 into the potato cells by osmosis because the cells have a higher solute concentration than the surrounding dilute salt solution.
The water therefore moves down the concentration gradient, from the region of higher water concentration outside to the lower concentration inside.
As water enters the cells, they become turgid, increasing the overall mass of the chip.

Examiner tips

  • Use the term "osmosis" and explain the concentration gradient. Mention the cells become turgid to justify the mass increase. Keep the answer concise and use the exact wording from the mark scheme.

Common mistakes

  • Confusing the direction of water movement. Forgetting to mention the cells become turgid. Using vague terms like "water enters" without linking to osmosis.

Mark scheme (4 marks)

  1. Water moves into the potato cells by osmosis
  2. The potato cells have a lower water concentration / higher solute concentration than the surrounding solution
  3. Water moves down a concentration gradient / from a region of high water concentration to low water concentration
  4. The cells become turgid, increasing the overall mass of the chip

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