The plant hormone abscisic acid (ABA) is involved in the regulation of photorespiration. Based on this information, ABA likely plays a role in

Question

A.  the opening and closing of stomata.
B.  the photoelectric effect.
C.  cyclic photophosphorylation.
D.  noncyclic photophosphorylation.

Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?

  Gather Content
What do you already know about photo respiration in photosynthesis? What other information is related to the question?

  Choose Answer
Do you have all the information needed to determine what processes ABA regulates in plants?

  Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

A.  the opening and closing of stomata.

Clarify Question
What is the key concept addressed by the question?
        · The question asks you to determine the role of ABA based on its role in photorespiration during photosynthesis.
What type of thinking is required?
        · You are being asked to dissect, or analyze, how ABA might help to regulate photo respiration in plants.

  Gather Content
What do you already know about photo respiration in photosynthesis? What other information is related to the question?
        · Recall that the key enzyme during Calvin cycle carbon fixation is rubisco. This enzyme is essential in taking inorganic carbon dioxide from the air and fixing it in an organic molecule, and under those conditions works as a carboxylase enzyme. However, rubisco also operates as an oxygenase enzyme. Rubisco carboxylase is associated with normal Calvin cycle production of G3P and regeneration of RuBP, whereas rubisco oxygenase activity prevents RuBP from proceeding in the Calvin cycle.
        · Given the potentially adverse effects of photo respiration, how can ABA be used to regulate this process?

  Choose Answer
Do you have all the information needed to determine what processes ABA regulates in plants?
        · Although the answers seem a little complicated, the correct answer is fairly straightforward. If you want to minimize rubisco oxygenase activity and maximize carboxylase activity, what environmental factors would you change in order to do so? Photo respiration is increased when carbon dioxide is low or oxygen is high. By manipulating when stomata open and close, a plant can regulate the relative concentration of both gases, and in this way promote rubisco carboxylase activity. The molecule a plant uses to help regulate stomata opening and closing is ABA.

  Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        · Answering this question correctly depended on your ability to analyze how ABA might help regulate photorespiration during photosynthesis.
        · If you got the correct answer, good job! If you got an incorrect answer, did you remember how photo respiration works? Did you remember that rubisco is both a carboxylase and an oxygenase that is sensitive to levels of carbon dioxide and oxygen? Were you able to correlate ABA with the ability of the plant to open and close stomata and thereby regulate the relative amounts of oxygen and carbon dioxide?