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plasmalyse. On the other hand, if a plant cell is placed in a solution with lower total solute concentration (less negative ys), it will gain water until the turgor pressure counteracts the difference in ys. As a small, uncharged molecule, water can directly cross the lipid bilayer. However, a family of aquaporins(proteins that function as water channels) have been identified. Aquaporins have been shown to play a role in water transport in the mammalian kidney. Recently, aquaporins have also been identified in plant cells. III. Implications Plants can manipulate the movement of solutes into particular compartments by transporting them using the electrical or chemical gradients set up by the proton pump. The movement of solutes influences the movement of water; water will tend to move into compartments with high solute concentrations.

A. Stomata

36.11

1. Open due to change in turgor pressure One example of this is the movement of water into guard cells that causes an increase in turgor pressure and results in a cell shape change that opens the stomata.

2. Mechanism

a. Active transport of H+ out of cell b. Increased membrane potential causes K+ influx c. Coupled transport brings Cl- into cell d. Increased solute concentration(large -ys) ‘ water influx

B. Transpiration

36.8

The rate of water loss through the stomata is also governed by Fick's law. Flux is the transpiration rate. The difference in water potential between the inside and the outside drives the movement of water and the resistance to movement is influenced by the degree of stomatal openning. (Campbell, 4th, pp. 692-696, 700-703) Review: Campbell 712-713, Self-quiz Q#1-5, 10, STS Q#1 ISP chapter 36 self-quiz