Through which pores do most gases enter and leave a leaf?
Reveal answer
The stomata (mainly on the lower epidermis).
Key words: stomata
2(g) GAS EXCHANGE · RECALL
2.40B Diffusion in plant gas exchange
15 recall questions · Biology only (B): not in Science (Double Award). Answer from memory, reveal the answer, then rate yourself. Ratings stay on this device.
Ratings are saved in this browser on this device, under a KS4 key kept separate from International A Level recall. Written answers are temporary and cleared when you leave the page. Use Reset to clear the ratings on this device.
Why does carbon dioxide move into a leaf in daylight?
Reveal answer
Photosynthesis uses CO₂ → concentration in the air spaces falls → CO₂ diffuses in from the air.
Key words: diffuses · concentration
Which leaf tissue has large air spaces that let gases reach every cell?
Reveal answer
The spongy mesophyll.
Key words: spongy
What is meant by the term diffusion?
Reveal answer
Net movement of particles down a concentration gradient due to random motion.
Key words: diffusion
What is meant by the term gas exchange?
Reveal answer
Movement of respiratory or photosynthetic gases between an organism and its environment.
Key words: gas exchange
Factors affecting gas diffusion: for Concentration gradient, give the change and the effect.
Reveal answer
Change: Steeper difference. Effect: Greater net movement per unit time.
Key words: Concentration gradient
Factors affecting gas diffusion: for Surface area, give the change and the effect.
Reveal answer
Change: Larger exchange area. Effect: More particles cross simultaneously.
Key words: Surface area
Factors affecting gas diffusion: for Diffusion distance, give the change and the effect.
Reveal answer
Change: Thinner barrier. Effect: Shorter route and faster exchange.
Key words: Diffusion distance
Factors affecting gas diffusion: for Medium renewal, give the change and the effect.
Reveal answer
Change: Ventilation or circulation. Effect: Maintains gradients.
Key words: Medium renewal
True or false, and why? “Diffusion means all molecules move in one direction.”
Reveal answer
False. Molecules move randomly both ways; only the net movement follows the gradient.
True or false, and why? “Cells spend ATP to push oxygen across alveoli.”
Reveal answer
False. Oxygen crosses mainly by diffusion; ventilation and circulation maintain gradients.
True or false, and why? “A concentration gradient is a physical slope.”
Reveal answer
False. It is a difference in concentration across distance.
Why does oxygen diffuse out of a leaf in bright light?
Reveal answer
Photosynthesis makes O₂ faster than respiration uses it → higher concentration in the air spaces than outside → diffuses out through the stomata.
Key words: concentration · stomata
Why does carbon dioxide diffuse out of a leaf at night?
Reveal answer
No photosynthesis, but respiration continues → CO₂ concentration in the air spaces rises above the outside air → diffuses out.
Key words: concentration
Suggest why a leaf with petroleum jelly on its lower surface takes in much less carbon dioxide.
Reveal answer
The jelly blocks the stomata on the lower surface → CO₂ cannot diffuse in.
Key words: stomata