4.5.3: Chapter Summary

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Melissa Ha, Maria Morrow, & Kammy Algiers
Yuba College, College of the Redwoods, & Ventura College via ASCCC Open Educational Resources Initiative

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Water and minerals move through the xylem, and sugars move through the phloem. Water potential and transpiration influence how water is transported through the xylem in plants as described by the cohesion-tension theory. Water potential (Ψ) is a measure of the difference in potential energy between a water sample and pure water and is influenced by solute concentration, pressure, gravity, and matric potential. Transpiration is primarily regulated by stomatal opening and closure. Roots must absorb water to replace the water lost through transpiration, and the high solute concentrations in the vascular cylinder results in root pressure. Assimilate containing sucrose move from sources to sinks through the plant’s phloem. Phloem loading increases solute concentration and causes water to move by osmosis from the xylem into the phloem. The positive pressure that is produced pushes water and solutes down the pressure gradient. The sucrose is unloaded into the sink, and the water returns to the xylem vessels.

After completing this chapter, you should be able to...

Define water potential and explain how it is influenced by solutes, pressure, gravity, and the matric potential.
Explain which components of water potential plants can manipulate and describe how.
Define transpiration and identify how environmental factors affect transpiration rate.
Describe the various adaptations that help plants reduce transpiration rate.
Relate the pattern of cell wall thickening in guard cells to their function.
Explain the mechanism by which blue light triggers stomatal opening.
Explain the mechanism by which water stress, signaled by abscisic acid, triggers stomatal closure.
Explain how water moves upward through a plant according to the cohesion-tension theory.
Provide experimental evidence for the cohesion-tension theory.
Explain the function of root hairs.
Define root pressure and explain its mechanism.
Contrast the three pathways of water movement through the roots and identify each cell type or tissue involved.
Distinguish between sources and sinks and provide examples of each.
Explain the process of phloem loading, distinguishing between apoplastic and symplastic pathways.
Explain how assimilate translocations through the phloem according to the pressure-flow hypothesis.

Attribution

Curated and authored by Melissa Ha using 30.5 Transport of Water and Solutes in Plants from Biology 2e by OpenStax (licensed CC-BY). Access for free at openstax.org.

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