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phospholipid molecules in the lipid bilayer via simple diffusion, as previously described, and (2) by moving through aquaporins-integral membrane proteins that function as water channel- Osmosis occurs only when a membrane is permeable to water but is not permeable to certain solutes.Aquaporins-integral membrane proteins that act as water channelsosmotic pressure
-the higher the concentration of solute, the higher the solutions osmotic pressure- The amount of pressure needed to restore the starting condition equals the osmotic pressure.- Notice that the osmotic pressure of a solution does not produce the movement of water during osmosis. Rather it is the pressure that would prevent such water movement.Tonicity- Because the osmotic pressure on both sides of the plasma membrane (which is selectively permeable) is the same, cell volume remains relatively constant. When body cells are placed in a solution having a different osmotic pressure than cytosol, however, the shape and volume of the cells change. As water moves by osmosis into or out of the cells, their volume increases or decreases. A solution’s tonicityis a measure of the solution’s ability to change the volume of cells by altering their water contentisotonic solution-any solution in which a cell, for example a red blood cell, maintains its normal shape and volume.- The concentrations of solutes that cannot cross the plasma membrane are the same on both sides of the membrane in this solution.hypotonic solution-a solution that has a lowerconcentration of solutes than the cystol inside the RBCs. (0.9% NaCl)-Lower concentration of solutes means a higher concentration of water. Water rushes into the cell faster than it can leave, so the cells swell up and eventually burst. Hemolysis-the rupture of red blood cells in a hypotonic solution.Lysis-the rupture of other types of cells due to placement in a hypotonic solutionhypertonic solution-has a higherconcentration of solutes than the cystol inside the RBCs. (ex. 2%NaCl solution)-water molecules move out of the cells faster than they enter, causing the cell to shrink. Crenation-shrinkage of cells. active transport- Some polar or charged solutes that must enter or leave body cells cannot cross the plasma membrane through any form ofpassive transport because they would need to move “uphill,” against their concentration gradients. Such solutes may be able to cross the membrane by a process called active transport. Active transport is considered an active process because energy is required for carrier proteins to move solutes across the membrane against a con- centration gradient.- Two sources of cellular energy can be used to drive active transport: (1) Energy obtained from hydrolysis of adenosine triphosphate (ATP) is the source in primary active transport; (2) energy stored in an ionic concentration gradient is the source in secondary active transport.- Like carrier-mediated facilitated diffusion, active transport processes exhibit a transport maximum and saturation.