Explain how facilitated diffusion differs from active transport in terms of energy use and direction of movement across the plasma membrane.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Facilitated diffusion does not require ATP or metabolic energy, whereas active transport requires ATP.
Facilitated diffusion moves substances down their concentration gradient (from high to low concentration).
Active transport moves substances against their concentration gradient (from low to high concentration).
Both use integral transmembrane proteins – facilitated diffusion uses channel or carrier proteins, while active transport uses carrier or pump proteins that undergo a conformational change driven by ATP hydrolysis.
Facilitated diffusion moves substances down their concentration gradient (from high to low concentration).
Active transport moves substances against their concentration gradient (from low to high concentration).
Both use integral transmembrane proteins – facilitated diffusion uses channel or carrier proteins, while active transport uses carrier or pump proteins that undergo a conformational change driven by ATP hydrolysis.
Examiner tips
- Use the word "does not require" for facilitated diffusion and "requires" for active transport. State the direction of movement relative to the concentration gradient. Mention the type of protein involved and note the ATP‑driven conformational change for active transport.
- Keep the answer concise – 4 marks can be earned with 4 short points.
Mark scheme (4 marks)
- Facilitated diffusion does not require ATP / metabolic energy, whereas active transport does require ATP / metabolic energy.
- Facilitated diffusion moves substances down / along their concentration gradient (from high to low concentration).
- Active transport moves substances against / up their concentration gradient (from low to high concentration).
- Both processes use (integral / transmembrane) proteins — facilitated diffusion uses channel or carrier proteins, and active transport uses carrier / pump proteins — but only active transport involves a conformational change driven by ATP hydrolysis.
Key terms in this question
facilitated diffusion · active transport
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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