How do guard cells open a stoma?
Reveal answer
Water enters guard cells by osmosis → they become turgid → curve apart → pore opens.
Key words: osmosis · turgid
2(g) GAS EXCHANGE · RECALL
2.43B Stomata and gas exchange
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What is meant by the term flaccid?
Reveal answer
Lacking turgor after water loss.
Key words: flaccid
What is meant by the term abscisic acid?
Reveal answer
A plant hormone involved in responses including stomatal closure during water stress.
Key words: abscisic acid
Open and closed stomata: for Guard-cell solute concentration, give the open stoma and the closed stoma.
Reveal answer
Open stoma: Higher. Closed stoma: Lower.
Key words: Guard-cell solute concentration
Open and closed stomata: for Water movement, give the open stoma and the closed stoma.
Reveal answer
Open stoma: Net entry by osmosis. Closed stoma: Net exit by osmosis.
Key words: Water movement
Open and closed stomata: for Guard-cell state, give the open stoma and the closed stoma.
Reveal answer
Open stoma: Turgid and curved. Closed stoma: Flaccid/less curved.
Key words: Guard-cell state
Open and closed stomata: for Gas and water movement, give the open stoma and the closed stoma.
Reveal answer
Open stoma: Greater exchange and transpiration. Closed stoma: Restricted exchange and reduced transpiration.
Key words: Gas and water movement
True or false, and why? “Guard cells physically push gas through the pore.”
Reveal answer
False. They alter aperture; gases move by diffusion.
True or false, and why? “Stomata always open in light.”
Reveal answer
False. Water stress and other signals can override a light response.
True or false, and why? “Closing stomata stops all water loss.”
Reveal answer
False. It reduces stomatal loss, but cuticular water loss and incomplete closure remain.
How do guard cells close a stoma?
Reveal answer
Water leaves the guard cells by osmosis → they become flaccid → the pore closes.
Key words: flaccid
Which cells control the size of a stomatal pore?
Reveal answer
A pair of guard cells.
Key words: guard cells
Why do many stomata close at night?
Reveal answer
No light → no photosynthesis, so CO₂ is not needed → closing reduces water loss.
Key words: water loss
Why can closing stomata on a hot day slow photosynthesis?
Reveal answer
Less carbon dioxide diffuses in → CO₂ becomes the limiting factor.
Key words: carbon dioxide
What is the pore between two guard cells called?
Reveal answer
A stoma (plural stomata).
Key words: stoma