# 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.

> AQA A-Level Biology (7402) — 3.2.3 Transport Across Membranes · Explain · 5 marks

> During intense exercise, muscle cells use glucose rapidly for respiration. Glucose must move from the blood into the muscle cells to maintain the supply.

## Mark scheme (5 marks)

1. Glucose cannot move by diffusion because the concentration gradient is in the wrong direction (glucose is higher inside the cell than in the blood)
2. Active transport is used to move glucose into the muscle cells
3. Active transport moves substances against a concentration gradient
4. Active transport requires energy in the form of ATP / from respiration
5. Carrier proteins in the cell membrane are used to transfer the glucose into the cell

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