What is meant by the term internal surface area?
Reveal answer
Total moist cell-wall area exposed to leaf air spaces.
Key words: internal surface area
2(g) GAS EXCHANGE · RECALL
2.42B Leaf adaptations for gas exchange
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What is meant by the term transpiration?
Reveal answer
Loss of water vapour from plant surfaces, mainly through stomata.
Key words: transpiration
Leaf structure and gas exchange: for Broad, thin lamina, give the gas-exchange effect and the trade-off or support.
Reveal answer
Gas-exchange effect: Large area and short diffusion distance. Trade-off or support: Large exposed area can increase water loss.
Key words: Broad, thin lamina
Leaf structure and gas exchange: for Spongy air spaces, give the gas-exchange effect and the trade-off or support.
Reveal answer
Gas-exchange effect: Rapid internal gas pathway and large cell surface. Trade-off or support: Moist surfaces lose water vapour.
Key words: Spongy air spaces
Leaf structure and gas exchange: for Stomata, give the gas-exchange effect and the trade-off or support.
Reveal answer
Gas-exchange effect: Adjustable connection to atmosphere. Trade-off or support: Opening couples CO₂ uptake to transpiration.
Key words: Stomata
Leaf structure and gas exchange: for Waxy cuticle, give the gas-exchange effect and the trade-off or support.
Reveal answer
Gas-exchange effect: Limits diffusion through epidermis. Trade-off or support: Conserves water while pores provide controlled exchange.
Key words: Waxy cuticle
Leaf structure and gas exchange: for Xylem, give the gas-exchange effect and the trade-off or support.
Reveal answer
Gas-exchange effect: Maintains moist mesophyll surfaces. Trade-off or support: Replaces transpired water.
Key words: Xylem
True or false, and why? “Air spaces are empty and have no function.”
Reveal answer
False. They form low-resistance pathways for gas diffusion.
True or false, and why? “A broad leaf only helps gas exchange because it has more stomata.”
Reveal answer
False. It also supports large internal surface area and light capture.
True or false, and why? “The waxy cuticle should cover stomata to stop water loss.”
Reveal answer
False. That would block regulated gas exchange; stomata provide controlled openings.
Give three ways a leaf is adapted for gas exchange.
Reveal answer
Large surface area; thin (short diffusion distance); air spaces in the spongy mesophyll; many stomata.
Key words: surface area · thin · stomata
Why does a thin leaf exchange gases quickly?
Reveal answer
Short diffusion distance from the stomata to every mesophyll cell → gases reach cells fast.
Key words: diffusion distance
Which surface of a broad leaf usually has the most stomata?
Reveal answer
The lower epidermis.
Key words: lower
Suggest why having most stomata on the lower surface helps a leaf.
Reveal answer
The lower surface is shaded and cooler → less evaporation → less water loss, while gas exchange still happens.
Key words: water loss
Why are the cell walls of mesophyll cells kept moist?
Reveal answer
Gases dissolve in the water film → then diffuse into the cells.
Key words: dissolve