Does not require metabolic energy. Depends on the concentration gradient to move things into and out of the cells. When carrier molecules become saturated they transport at their maximum rate. All of available protein channels are working at their max rate. Cannot move substances against their concentration gradients 2. Osmosis - passive It is the diffusion of water (solvent) across a selectively permeable membrane Water tends to move across membranes from an area where there is more water (more water, less solutes), to an area where there is less water (less water, more solutes). Aquaporins, membrane rearrangement Osmotic pressure - if there is a solution which is very concentrated with solutes, water will tend to move into it more strongly than into a weaker solution. This tendency of water to move into a solution is known as osmotic pressure Osmolarity Osmolarity deals with the total amount of solvent and solute in solutions. When solvent and solutes are allowed to move freely there is no net change in the volume of solutions on either side of the membrane. Tonicity Cells have a tendency to shrink or swell when placed in solution, and these are called Isotonic- Same solute and water conc. in and out of cell. Hypotonic- more water inside cell then outside. Hypertonic- more solute inside cell then outside. If a cell is placed in a hypotonic solution, the inside of the cell will have more solutes than the solution, so water will rush in and cause it to lyse . If a cell is placed in an isotonic solution, the inside of the cell will have the same concentration of ions as the solution, so there is no net movement of water into or out of the cell. If a cell is placed in a hypertonic solution, there is more water present in the interior of the cell than in the external solution so water leaves the cell and it becomes crenated 5
Nur 0012 Tonicity deals with only the non-penetrating solutes that will cause movements of water. Sketch a cell in each of the three types of solutions and note which direction water will flow. 4. Active Transport Mechanisms Transport mechanisms involve carrier molecules within the plasma membrane that carry large molecules through the plasma membrane. All mediated transport mechanisms have 3 characteristics in common: 1. Specificity – 2. Competition – 3. Saturation – Primary Active Transport Requires energy provided by the breakdown of ATP to move substances from one side of the membrane to the other. Active transport can move substances against their concentration gradients as long as there is adequate ATP and carrier molecules Active transport can also exchange one substance for another as in the NA+/K+ pump.
You've reached the end of your free preview.
Want to read all 10 pages?
- Fall '16