Question 4
Why does carbon dioxide move into a photosynthesising leaf without the plant spending any energy?
The right answer is the one marked above.
Because the leaf is using it up, so its concentration inside is lower than outside. Gas diffuses from where it is more concentrated to where it is less, on its own, with no pump and no energy.
Stomata are holes, not valves with a direction. Which way a gas moves through one depends only on which side it is more concentrated.