A plant is exposed to a toxin that blocks ABA receptor sites in the plasma membrane. What is the likely consequence of this exposure?

Question

A. Oxygen deprivation will trigger the release of ethylene, which will in turn suppress root growth.
B. Gibberellin production will increase, allowing the plant to access more nutrients in the soil.
C. ABA will enter the cells by an alternative route and normal function will be restored.
D. The plant will lose excess water through transpiration and suffer dehydration.
E. The guard cells will become flaccid and gas exchange will cease.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain?

Gather Content
· What do you already know about ABA? How does it relate to the question?

Consider Possibilities
· What other information is related to the question? Which information is most useful?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

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

D.  The plant will lose excess water through transpiration and suffer dehydration.

Clarify Question
· What is the key concept addressed by the question?
        o The key concept is the function of ABA.
· What type of thinking is required?
        o Apply, because you must take what you know about ABA and apply it to a new situation.
· What key words does the question contain?
        o ABA receptor sites, which are molecules that receive ABA and signal the cell to open ion channels.

Gather Content
· What do you already know about ABA?  How does it relate to the question?
        o The hormone ABA is abscisic acid.
        o ABA binds to receptors in the cell membrane.
        o As a result, K+ and other ion channels open.
        o This causes guard cells to lose K+.
        o Water loss follows, and turgor pressure decreases.
        o This causes guard cells to close.
        o Closed guard cells become flaccid, and cover the openings of the stomata.
        o This prevents excess water loss.
 
Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o ABA acts on the guard cells that surround the stomata, so root function is not impacted.
        o If guard cells do not become flaccid, stomata will remain open, and gas exchange can occur.
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o As soon as you identify the function of ABA, you can deduce what would happen to a plant that did not have functional ABA receptors.
 
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?
        o This question requires you to connect what you know about ABA function in a normal plant with a sudden loss of ABA activity due to the toxin. First, you must recognize that ABA
functions in guard cells that surround the stomata of the leaf. When you recall that ABA causes the stomata to close, you know that by closing, the stomata are preventing excess water loss. Therefore, if ABA is not received by the guard cells, the cells will remain open, which would allow evaporation of water without limit.