Explain the role of carrier proteins in active transport across a cell membrane.

Cambridge International IGCSE Biology (0610) — 3.3 Active transport · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Carrier proteins are embedded in the cell membrane.
Molecules from the low‑concentration side bind to the carrier protein.
The carrier protein changes shape using energy from respiration.
The molecule is moved through the membrane against the concentration gradient and released on the high‑concentration side.

Examiner tips

  • Use the word "carrier protein" and "embedded in the membrane". Show the sequence: binding, shape change, movement, release. Mention energy from respiration (ATP) as the source of energy.
  • common_mistakes
  • :
  • Forgetting to state that the carrier protein is embedded in the membrane. Saying the molecule moves down the gradient instead of against it. Omitting the role of energy from respiration.

Mark scheme (4 marks)

  1. Carrier proteins are embedded in the cell membrane
  2. Molecules from the low-concentration side bind to the carrier protein
  3. The carrier protein changes shape using energy from respiration
  4. The molecule is moved through the membrane against the concentration gradient and released on the high-concentration side

Key terms in this question

active transport · carrier proteins

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