Answer
The opening and closing of stomata are controlled by the following: 1) light (opening makes sense when dawn comes and carbon dioxide is needed for photosynthesis); 2) carbon dioxide depletion (again, opening makes sense to let carbon dioxide into the leaf for photosynthesis); 3) circadian rhythms, which help anticipate the time when carbon dioxide is needed for photosynthesis; and 4) environmental stresses, which raise levels of the hormone, abscisic acid, when water is scarce, closing stomates to conserve water.
Work Step by Step
This question just asks you to summarize the four items listed on p. 796.
