Which of the following must occur in order to maintain a high pressure potential within guard cells?

Question

A.  Potassium ions must be actively transported out.
B.  Energy must be constantly expended.
C.  Water must exit guard cells by osmosis.
D.  Stomata must take up more oxygen and less carbon dioxide.
E.  The rate of transpiration must increase.

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 how guard cells function? How does it relate to the question?
 
Consider Alternatives
· What other information is related to the question? Which information is most useful?
 
Choose Strategy
· 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

B.  Energy must be constantly expended.

Clarify Question
· What is the key concept addressed by the question?
        o The key concept is the mechanical function of the guard cells.
· What type of thinking is required?
        o Apply, because knowledge of how the guard cells function must be applied to a different concept.
· What key words does the question contain?
        o High pressure potential, which is a high hydrostatic pressure inside a cell.
        o Guard cells, which open and close stomata on the leaf surface.
 
Gather Content
· What do you already know about how guard cells function? How does it relate to the question?
        o High pressure potential is directly related to turgor.
        o Turgor is maintained in plant cells by the active uptake of K+ and other ions.
        o As solute concentration increases through this active uptake, water potential decreases.
        o Water flows into the cell, toward the area of lower water potential.
        o This and any active process requires the use of energy.
 
Consider Alternatives
· What other information is related to the question? Which information is most useful?
        o Gas exchange is not directly related to the mechanics of the guard cells.
        o Any loss of water or ions would cause the guard cells to lose turgor and pressure potential.
 
Choose Strategy
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o To answer this question you must connect the concepts of pressure potential and turgor. To maintain turgor, ions must be actively transported (using ATP) into the cell. This lowers the water potential, which brings water in and increases turgor and the pressure potential.
 
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 The question is asking you to relate the active uptake of ions with increased turgor. If you arrived at the correct answer, well done! If you came up with an incorrect answer, where did the process break down? Did you remember that as pressure potential increases, turgor increases. Turgor is maintained by the active uptake of K+ and other ions.