Describe the journey of an oxygen molecule from the trachea to the bloodstream, naming the structures it passes through in the correct order.

Eduqas GCSE Biology — 1.2.2 The respiratory system · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Oxygen enters the trachea, then passes into the bronchi, continues into the bronchioles, reaches the alveoli, and finally diffuses across the alveolar wall into the blood capillaries.

Examiner tips

Use the exact sequence of structures; a single sentence is acceptable.
Show the final step as diffusion into capillaries to get all marks.
Avoid extra words that distract from the required order.
Use UK spelling (e.g., ‘capillaries’).

Common mistakes

Including the larynx or pharynx, which are not part of the respiratory tract for this question.
Omitting the bronchioles or alveoli, breaking the required sequence.
Writing the answer in a paragraph form that obscures the order.

Mark scheme (4 marks)

Oxygen passes from the trachea into the bronchi
Oxygen passes from the bronchi into the bronchioles
Oxygen reaches the alveoli (from the bronchioles)
Oxygen diffuses across the alveolar wall / thin membrane into the blood / capillaries

Key terms in this question

trachea