# Explain how oxygen moves from the air sacs (alveoli) in the lungs into the blood during breathing.

> AQA GCSE Biology (8461) — 4.1.3 Transport in cells · Explain · 4 marks

> The alveoli have a large surface area and are surrounded by a dense network of capillaries. The blood arriving at the alveoli has a low concentration of oxygen.

## Mark scheme (4 marks)

1. Oxygen moves by diffusion
2. Oxygen moves from a higher concentration in the alveoli to a lower concentration in the blood
3. There is a concentration gradient between the alveoli and the blood
4. No energy (from respiration) is required / it is a passive process

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