Identify alveoli and their associated capillaries in a diagram
Separate the air space from the blood network at the gas-exchange boundary.
Section 11.1 · Gas exchange in humans
Core and Extended; Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Recall the four gas-exchange features.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which compartment contains ventilated air?
What you will learn
- Two routes meet at a thin boundary
- Identify by connection and compartment
Identify alveoli and their associated capillaries in a diagram
Two routes meet at a thin boundary
Alveoli are air spaces reached by small airways. Associated capillaries form a blood network close to the alveolar walls. The two routes approach each other at the exchange barrier, allowing oxygen and carbon dioxide to diffuse between air and blood under the usual concentration differences.
The original enlargement shows I as an alveolar air space and J as the surrounding capillary route. The capillary drawing is opened out to make its course visible; its apparent page width does not establish its real diameter. Blood stays in vessels while air stays on the air-space side.
Identify by connection and compartment
An alveolar opening connects towards an air-carrying bronchiole; a capillary connects to other blood vessels and contains blood. These connections help in a new image when the colours or orientation differ. Alveolus is singular and alveoli is plural; neither is the name of the whole lung.
The identification task is different from claiming that every line in a microscopic image is a capillary. Use the supplied boundaries, blood-cell evidence and source labels. A schematic can explain the relationship but cannot replace practical competence in using real specimens or establish clinical findings.
Pause and explain
Which evidence best distinguishes a capillary from a bronchiole in the supplied diagram?
Worked example
Identify I and J in the exchange enlargement.
Show the worked solution
- I is reached by the air route.
- J is the associated blood route.
Answer I alveolar air space; J associated capillary.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Identify I and J and state what moves through each route.
Give me a hint
Distinguish air and blood.
Compare my reasoning
- I is the alveolar air space receiving air.
- J is a capillary carrying blood.
I alveolus with air; J capillary with blood.
Look for these in your work
- Identify both
- Name their different contents
Explain why oxygen exchange does not require air to flow into the capillary as a bulk stream.
Give me a hint
Individual gas molecules cross a boundary.
Compare my reasoning
- Air and blood remain in different compartments.
- Oxygen diffuses across the thin exchange barrier.
Oxygen diffuses across the separating surface into blood; bulk air need not enter the capillary.
Look for these in your work
- Retain the boundary
- Name diffusion
A new schematic reverses the colours of air and blood routes. Does this reverse the anatomical identities?
Give me a hint
Follow the labelled connections.
Compare my reasoning
- Colours are conventions.
- The air-space and blood-route connections still determine identity.
No; alveoli and capillaries are identified by their compartments and connections, not a fixed colour code.
Look for these in your work
- Reject colour-only identification
- Use route evidence
Common mistakes
- Treating an alveolus as a blood cell.
- Assuming any narrow line is a capillary.
What can you explain now?
Which evidence best distinguishes a capillary from a bronchiole in the supplied diagram?
Compare with the explanation
Its blood-route connection beside the alveolus
Use the compartment and route.
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Make it stick
Identify the two compartments and draw opposite oxygen and carbon-dioxide exchange arrows.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.