Critical Thinking Activities - Chapter 37

Question 1. There are two hypotheses for what triggers stomates to open and close. One states flavin pigments absorb blue light and this pigment then activates the proton pump. The second responds to CO2; as its concentration rises, a membrane receptor inactivates the proton pump. Which, if either, do the following observations support? a) The clear guard cells of a ladyslipper orchid lack chloroplasts, yet the guard cells regularly open and close. b) Stomates do not respond when exposed to a narrow band of green light. c) The cells of wilting leaves produce abscisic acid; abscisic acid causes guard cells to close.

Question 2. Nearly all deciduous tree leaves have all stomates on the bottom side; none on the top. On the other hand, corn, oats, lilies, wheat, etc. have as many if not more stomates on the top side of the leaf. Why?

Answers are available to instructors in the Instructor's Manual.
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