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All 12 Flashcards — Properties of gas-exchange surfaces
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Question
What is a gas-exchange surface?
Answer
The thin boundary where gases pass between the body and the environment — e.g. the wall of an **alveolus** in the lung.
Question
By what process do gases cross a gas-exchange surface?
Answer
**Diffusion** — the passive net movement of particles from **high** to **low** concentration.
Question
Why is no energy needed for gas exchange?
Answer
Diffusion is **passive**: particles move on their own down the **concentration gradient**, so no energy (ATP) is used.
Question
Name the four features of a good gas-exchange surface.
Answer
**Large** surface area, **thin** (short diffusion distance), **moist** and **permeable**.
Question
Why does a large surface area help gas exchange?
Answer
More gas can diffuse across **at the same time**, so exchange is faster.
Question
Why does a thin surface help gas exchange?
Answer
The wall is only **one cell thick**, giving a **short diffusion distance**, so diffusion is fast.
Question
Why is the gas-exchange surface moist?
Answer
A thin film of water lets the gases **dissolve** before they cross the membrane.
Question
In which direction does oxygen diffuse in the lungs?
Answer
From the **alveolar air into the blood** (from higher to lower oxygen concentration).
Question
In which direction does carbon dioxide diffuse in the lungs?
Answer
From the **blood into the alveolar air** (from higher to lower carbon dioxide concentration).
Question
How does ventilation help maintain the gradient?
Answer
Fresh air keeps alveolar **oxygen high** and **carbon dioxide low**, so the gradient stays steep.
Question
How does blood flow help maintain the gradient?
Answer
It carries blood away and brings fresh blood in, keeping capillary **oxygen low** and **carbon dioxide high**.
Question
What happens to diffusion if the concentrations on both sides become equal?
Answer
Net diffusion **stops** — which is why the gradient must be kept **steep** by ventilation and blood flow.
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Full study notes for Properties of gas-exchange surfaces
Topic 2.6 hub
Gas exchange
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