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Question 81

A plant growing in dry soil is running short of water on a hot day. How do its stomata respond, and what does that response cost it?

  1. They open wider, and the plant cools down faster
  2. They close, and it costs nothing, since photosynthesis carries on unchanged
  3. They stay exactly as they were, since guard cells respond only to light
  4. They close, and less carbon dioxide can then enter the leafCorrect answer

Explanation

Guard cells short of water go limp and the pores between them shut, which is what saves the remaining water, but the same pores are the way in for the gas a leaf needs, so shutting them slows the reaction that builds sugar. Treating closure as free ignores that trade: a sealed leaf keeps its water and stops feeding itself at the same time.

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Question 81: A plant growing in dry soil is running short of water on a… · Plants and Photosynthesis · Questena