Plant Physiology

The Plant Cell, Jan 2014, www.plantcell.org © 2014 American Society of Plant Biologists. All rights reserved.

www.plantcell.org/cgi/doi/10.1105/tpc.114.tt0114

Study / exam questions (understanding and comprehension)

• True or false: Compared to molecules of similar molecular weight, water has an unusually high boiling point.

• Imagine two adjoining cells, the left one with a water potential of -0.5 MPa and the right one with a water potential of -0.2 MPa. Will the water move from Left to Right, or Right to Left?

• What is the source of energy that drives water movement through the plant body?

• The flow of water from soil to root is affected by both the water potential difference between soil and root and the conductance of the root.

o Describe a condition that would change the water potential gradient across the surface of the root.

o Describe a condition that would change the hydraulic conductance of the root system.

• What are aquaporins? In terms of Fick’s Law, which parameter do they affect?

• Describe three ways that aquaporin activity is regulated.

• How does the Casparian strip affect water movement into the plant?

• Identify and describe the three pathways through which water can move from the soil to the stele of the root.

• Xylem is described as a “vulnerable pipeline”: vulnerable to what?

• What are pit membranes, what are they composed of, and how do their structural properties affect cavitation resistance?

• Order these plants according to the water potential at which they experience 50%

loss of conductivity, from least negative to most negative: o Sugar maple o Mangrove o Cottonwood o Ceonothus

• Which are usually wider, tracheids or vessels? How does increased xylem diameter

affect flow and sensitivity to cavitation?

• What is one strategy that a plant with very wide vessels (e.g., grapevine) can use to avoid freezing-induced embolism formation?

• The high vein density of angiosperm leaves enables them to have a high rate of photosynthesis. Explain the connection between vein density and photosynthesis in terms of hydraulic conductance.

• Describe two ways that leaves can act as “disposable fuses” to protect the integrity of the water column in large braches.

• What are stomatal crypts and how do they influence transpiration: by changing driving force or conductance?

• You can check your understanding of the uptake and transport of water through this excellent interactive tutorial http://ats.doit.wisc.edu/biology/pb/wr/wr.htm. (At the time of publication, this was a functioning link – hopefully it still is.)