Explain why oxygen moves from the lungs into the blood during breathing.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Cells in the body constantly use oxygen during respiration. The blood arriving at the lungs has a low concentration of oxygen, while the air in the lungs has a high concentration of oxygen.
Model answer (4 marks)
Oxygen moves from the lungs into the blood by diffusion.
The concentration of oxygen is higher in the air of the lungs than in the blood.
Oxygen therefore moves down its concentration gradient, from the high concentration in the lungs to the low concentration in the blood.
This is a passive process and requires no energy.
The concentration of oxygen is higher in the air of the lungs than in the blood.
Oxygen therefore moves down its concentration gradient, from the high concentration in the lungs to the low concentration in the blood.
This is a passive process and requires no energy.
Examiner tips
- Use the word "diffusion" to identify the process.
- Mention the concentration gradient and the direction of movement.
- State that the process is passive and no energy is required.
- Keep the answer concise and use the exact terminology.
Mark scheme (4 marks)
- Identifies the process as diffusion
- States that there is a concentration gradient / difference in concentration between the lungs and the blood
- States that oxygen moves from a region of high concentration (lungs/air) to a region of low concentration (blood)
- States that no energy is required / it is a passive process
Related
- All Eduqas GCSE Biology revision notes →
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- Decode the mark scheme abbreviations →