Plant Physiology (Biology 327)
- Dr. Stephen G. Saupe; College of St. Benedict/ St.
University; Biology Department; Collegeville, MN 56321; (320) 363 - 2782;
(320) 363 - 3202, fax;
Exam Questions: Gas Exchange/Transpiration
- Both plants and animals must exchange gases with the environment. To do
this successfully required them to solve a number of "problems". Identify
the gas exchange problems that confront both plants and animals. Then describe how
these problems were "solved". Include a discussion of the
photosynthesis/transpiration compromise and why stomata are ideally suited for gas
exchange (i.e. anatomy, size, distribution, location).
- Explain the
mechanism by which guard cells open and close the stomata. Include in your
response a discussion of guard cell structure and mechanics (e.g.,
radial micellation, thickened inner walls), turgor pressure, solute
(osmotic) potential, and solutes (e.g., potassium ions,
carbohydrates, malate, chloride).
- Describe the
function and action of the H+-ATPase in the action of guard
cells. How do we know a proton pump is involved in guard cell action (e.g.,
vanadate, CCCP, fusicoccin)? Explain the mechanism by which this pump is
hypothesized to work (e.g., hyperpolarize membrane, voltage gated
- Data suggest
that potassium ions are the important solute regulating guard cell opening
while sucrose is important for closing guard cells. Explain why potassium
levels increase rapidly and then slowly decline during the day while sucrose
levels show the reverse pattern (they slowly increase during the day and
then decline a little more rapidly).
- Blue light is
a potent regulator of the proton pump. Include a description of how blue
light stimulates the pump through its interaction with zeaxanthin and
- Describe the
effect of light (PAR) on guard cell activity. Why do we expect light to play
a major regulatory role in guard cell action? How do we know photosynthesis
(PAR) is an important regulator of guard cell action? What is the function
of PAR/photosynthesis in guard cell action? Include a discussion of starch,
sucrose, chloroplastic pH, ATP synthesis, cytoplasmic carbon dioxide levels
and cytoplasmic pH.
- Calcium ions play a major role in the signal
pathway to close guard cells/stomata. Explain the role of calcium in guard
cell closure including a discussion of its role in increasing cytoplasmic
calcium concentrations (self-catalytic), its effect on chloride and
potassium ion concentrations, and its effect on the proton pump.
- Describe the effect of water stress on guard
cell activity. Why should water play a role in guard cell action? Include
a discussion of hydropassive and hydroactive controls. Explain the
mechanism of action for both, including the function and source(s) of ABA
and its mechanism of action (e.g., effect on calcium, ROS and other
01/07/2009 � Copyright by SG