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.)
