Lecture 06/Water transport

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[H⁺]

This is an unbalanced situation, like a bucket of water balanced on top of a door. It took work to get it up there, and that work is just waiting to dump the water on top of whoever opens the door. The potential energyin the proton concentration gradient and the charge gradient can be used to move other things. The charge gradientcan be used to allow positively-charged ions, such as K⁺to move into the cell by passive transport.

4. Cotransport

8.17, 36.2

Fig 8.16In plants, the movement of protons back into the cell is used to bring molecules such as NO₃^-and sucrose into the cell.

Q. If you have plant cells in a solution and you add sucrose, what happens to the pH of the surrounding solution as the sucrose is moved into the cells? protons move into the cell, so [H⁺] on the outside decreases, pH increases

II. Short range transport of H₂O in plants

Let's return to a more detailed examination of how water is moved into and out of cells. Diffusion of a substance across a membrane is governed by Fick's law.

A. Fick's law
Flux = DA(C₁-C₂)
X
Flux = flow of solute from 1 [!]2
A = area
X = thickness of barrier
C = concentration
D = diffusion coefficient (how easily solute passes through barrier)

Therefore, you can increase the rateof exchange by increasing the area or by maintaining a large concentration difference



		[H⁺]
This is an unbalanced situation, like a bucket of water balanced on top of a door. It took work to get it up there, and that work is just waiting to dump the water on top of whoever opens the door. The potential energyin the proton concentration gradient and the charge gradient can be used to move other things. The charge gradientcan be used to allow positively-charged ions, such as K⁺to move into the cell by passive transport.
	4. Cotransport		8.17, 36.2
Fig 8.16In plants, the movement of protons back into the cell is used to bring molecules such as NO₃^-and sucrose into the cell. Q. If you have plant cells in a solution and you add sucrose, what happens to the pH of the surrounding solution as the sucrose is moved into the cells? protons move into the cell, so [H⁺] on the outside decreases, pH increases II. Short range transport of H₂O in plants Let's return to a more detailed examination of how water is moved into and out of cells. Diffusion of a substance across a membrane is governed by Fick's law. A. Fick's law Flux = DA(C₁-C₂) X Flux = flow of solute from 1 [!]2 A = area X = thickness of barrier C = concentration D = diffusion coefficient (how easily solute passes through barrier) Therefore, you can increase the rateof exchange by increasing the area or by maintaining a large concentration difference