Explain why an athlete's muscle cells are able to absorb glucose from the blood even when the concentration of glucose inside the muscle cells is higher than the concentration of glucose in the blood.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
During intense exercise, muscle cells use glucose rapidly for respiration. Glucose must move from the blood into the muscle cells to maintain the supply.
Model answer (5 marks)
Glucose cannot move by simple diffusion because the concentration gradient is in the wrong direction – glucose is higher inside the muscle cell than in the blood.
Muscle cells therefore use active transport to move glucose into the cell.
Active transport moves substances against a concentration gradient.
The process requires energy, supplied as ATP from cellular respiration.
Carrier proteins in the cell membrane, such as GLUT4, are used to transfer glucose into the cell.
Muscle cells therefore use active transport to move glucose into the cell.
Active transport moves substances against a concentration gradient.
The process requires energy, supplied as ATP from cellular respiration.
Carrier proteins in the cell membrane, such as GLUT4, are used to transfer glucose into the cell.
Examiner tips
- Use the term ‘active transport’ and explain it moves against a gradient. Include that ATP is the energy source. Mention carrier proteins (e.g., GLUT4) to show mechanism. Keep each point concise to match the 5 marks.
Common mistakes
- Confusing diffusion with active transport. Forgetting to state that ATP is needed. Using the wrong carrier protein name or omitting it entirely.
Mark scheme (5 marks)
- Glucose cannot move by diffusion because the concentration gradient is in the wrong direction (glucose is higher inside the cell than in the blood)
- Active transport is used to move glucose into the muscle cells
- Active transport moves substances against a concentration gradient
- Active transport requires energy in the form of ATP / from respiration
- Carrier proteins in the cell membrane are used to transfer the glucose into the cell
Related
- All AQA A-Level Biology (7402) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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