Red blood cells need glucose for cellular respiration. Explain how glucose moves from the blood plasma into a red blood cell, and describe what happens to the rate of this movement when glucose concentration in the plasma is very high compared to inside the cell.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Red blood cells lack mitochondria and rely entirely on glucose obtained from the surrounding blood plasma to carry out cellular respiration.
Model answer (5 marks)
Glucose enters a red blood cell by diffusion across the cell membrane.
1. Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration.
2. The cell membrane is selectively permeable, allowing glucose to pass through.
3. When the glucose concentration in the plasma is very high compared with the inside of the cell, the concentration gradient becomes steeper.
4. A steeper gradient increases the driving force for diffusion.
5. Consequently, glucose diffuses into the cell at a faster rate.
1. Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration.
2. The cell membrane is selectively permeable, allowing glucose to pass through.
3. When the glucose concentration in the plasma is very high compared with the inside of the cell, the concentration gradient becomes steeper.
4. A steeper gradient increases the driving force for diffusion.
5. Consequently, glucose diffuses into the cell at a faster rate.
Examiner tips
- Use the word ‘diffusion’ and explain it as movement from high to low concentration.
- Mention the selective permeability of the membrane.
- Show the link between a steeper gradient and a higher rate of diffusion.
- Keep the answer concise and use the exact terminology from the mark scheme.
Common mistakes
- Confusing diffusion with active transport.
- Forgetting to state that the membrane is selectively permeable.
- Not linking the steeper gradient to a faster rate of movement.
Mark scheme (5 marks)
- Glucose moves by diffusion (across the cell membrane)
- Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration
- The cell membrane is selectively permeable / controls what enters and exits the cell
- When glucose concentration in the plasma is very high compared to inside the cell, the concentration gradient is steeper / larger
- A steeper concentration gradient means glucose diffuses into the cell at a faster rate
Key terms in this question
Related
- All WJEC A-Level Biology (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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