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3.3c
| Question | Answer |
|---|---|
| Osmosis is the net flow of water from one side of a selectively permeable membrane to the other. | It is crucial to the body’s water distribution (fluid balance). |
| Imbalances in ----- underlie such problems as diarrhea, constipation, hypertension, and edema (tissue swelling); ---- also is a vital consideration in intravenous (IV) fluid therapy. | osmosis |
| Osmosis | occurs through nonliving membranes, such as cellophane and dialysis membranes, and through the plasma membranes of cells. |
| Osmosis | The usual direction of net movement is from the more watery side, with a lower concentration of dissolved matter, to the less watery side, with a greater concentration of solute. |
| Osmosis | The reason for the accumulation of water on the high-solute side is that when water molecules encounter a solute particle, they tend to associate with it to form a hydration sphere |
| Osmosis | Even though this is a loose, reversible attraction, it does make those water molecules less available to diffuse back across the membrane to the side they came from |
| Osmosis | In essence, solute particles on one side of the membrane draw water away from the other side. Thus, water accumulates on the side with the most solute. |
| Osmosis | All of this assumes that the solute molecules in question can’t pass through the membrane, but stay on one side. |
| Osmosis | The rate and direction of ----- depend on the relative concentration of these nonpermeating solutes on the two sides of the membrane. |
| Significant amounts | of water pass even through the hydrophobic, phospholipid regions of a plasma membrane, but water passes more easily through channel proteins called aquaporins, specialized for water. |
| Cells can increase the rate of ---- by installing more aquaporins in the membrane or decrease the rate by removing them. | osmosis |
| kidney | Certain cells of the ------, for example, regulate the rate of urinary water loss by adding or removing aquaporins. |
| A cell can exchange a tremendous amount of water by osmosis. | In red blood cells, for example, the amount of water passing through the plasma membrane every second is 100 times the volume of the cell. |
| Under such conditions, the water level in side A would fall and the level in side B would rise. It may seem as if this would continue indefinitely until side A dried up. | This would not happen, however, because as water accumulated in side B, it would become heavier and exert more force, called hydrostatic pressure, on that side of the membrane. |
| This would cause some filtration of water from B back to A. At some point, the rate of filtration would equal the rate of “forward” osmosis, water would pass through the membrane equally in both directions, and net osmosis would slow down and stop | At this point, an equilibrium (balance between opposing forces) would exist. The hydrostatic pressure required on side B to halt osmosis is called osmotic pressure. The more nonpermeating solute there is in B, the greater the osmotic pressure. |
| If the solute concentration on side B was half what it was in the original experiment, would the fluid on that side reach a higher or lower level than before? Explain. | When the solute on side B is halved, less water moves there, so the fluid level is lower than before. |
| Reverse osmosis | is a process in which a mechanical pressure applied to one side of the system can override osmotic pressure and drive water through a membrane against its concentration gradient. |
| Reverse osmosis | This principle is used to create highly purified water for laboratory use and to desalinate seawater, converting it to drinkable freshwater—important for arid countries and ships at sea. |
| The body’s principal pump, the heart, drives water out of the smallest blood vessels (the capillaries) by reverse osmosis—a process called | capillary filtration |
| Blood plasma also contains albumin. | In the preceding discussion, side B is analogous to the high-protein bloodstream and side A to the low-protein tissue fluid surrounding the capillaries. |
| Water | leaves the capillaries by filtration, but this is approximately balanced by water reentering the capillaries by osmosis. |
Created by:
Russells3709