steepness of the concentration gradient across the membrane The number of

Steepness of the concentration gradient across the

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steepness of the concentration gradient across the membrane - The number of carriers available in a plasma membrane places an un upper limit, called the transport maximum , on the rate at which facilitated diffusion can occur - Once all the carriers are occupied, the transport maximum is reached, and a further increase in the concentration gradient does not increase the rate of facilitated diffusion - Thus, much like a completely saturated sponge can absorb no more water, the process of carrier-mediated facilitated diffusion exhibits saturation - Substances that move via carrier mediated facilitated diffusion are glucose, fructose, galactose, and some vitamins - Glucose is the body’s preferred energy source for making ATP, enters the body’s cells by carrier mediated facilitation as follows 1. Glucose binds to a specific type of carrier protein called the glucose transporter (GluT) on the outside surface of the membrane 2. As the transporter undergoes a change in shape, glucose passes through the membrane 3. The transporter releases glucose on the other side of the membrane - The selective permeability of the plasma membrane is often regulated to achieve homeostasis - For instance, the hormone insulin, via the action of the insulin receptor, promotes the insertion of many copies of glucose transporters into the plasma membrane of certain cells, thus the effect of insulin to elevate the transport maximum for facilitated diffusion of glucose into the cells, with more glucose transporters available, body cells can pick up glucose from the blood rapidly Osmosis - Type of diffusion in which there is net movement of a solvent through a selectively permeable - Like other types of diffusion, osmosis is s passive process - In living systems, the solvent is water, which moves by osmosis
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- In living systems, the solvent is water, which moves by osmosis across plasma membranes from an area of higher water concentration to an area of lower water concentration - During osmosis, water molecules pass through a membrane by 1. Moving between neighbouring phospholipid molecules in the lipid bilayer via simple diffusion 2. By moving through aquaporins – integral membrane proteins that function as water channels - Occurs only when a membrane is permeable to water but not permeable to certain solutes - Hydrostatic pressure : pressure exerted by a liquid - Osmotic pressure: solution with impermeable solute also exerts a force - Osmotic pressure of a solution is proportional to the concentration of the solute particles that cannot cross the membrane - The higher the solute, the higher the osmotic pressure - The amount of pressure needed to restore the starting condition equals the osmotic pressure - Normally, the osmotic pressure of the cytosol is the same osmotic pressure of the interstitial fluid outside cells - Because the osmotic pressure on both sides of the plasma membrane (which is selectively permeable) is the same, the cell volume remains relatively constant - When the body cells are placed in a solution having a different osmotic pressure than
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