Diffusion

• Temperature affects the rate of diffusion, with higher temperatures generally resulting in faster diffusion.
• Diffusion moves small non-polar molecules from an area of high concentration to an area of low concentration
• Lipid rafts have a higher concentration of cholesterol molecules. At high temperatures, these regions are more fluid than the surrounding membrane.
• Phospholipids and proteins are the structural components of the cell membrane.
• When biological membranes are frozen and then fractured. they tend to break along the middle of the cell bilayer because the integral membrane proteins are not strong enough to hold the bilayer together.
• An integral membrane protein must be amphipathic, with at least one hydrophobic region.
• Carrier proteins bind to a substance on one side of the membrane and release it on the other side.
• A channel protein forms a pore through which specific molecules can pass.
• The cell membranes of Antarctica fish might have a high percentage of polyunsaturated fatty acids.
• The fluid mosaic model has been refined to show that the membrane is only fluid across a very narrow temperature range.
• The movement of the hydrophobic gas nitrous oxide into a cell is an example of diffusion across the lipid bilayer.
• A carrier protein exhibits a specificity for a particular type of molecule.
• Water passes quickly through cell membranes because it moves through aquaporins in the membrane.
• Active transport requires energy from ATP.
• In passive transport, no energy input from ATP or other sources is required.
• In active transport, the concentration gradient is against the direction of spontaneous diffusion.
• Tonicity refers to the ability of a solution to cause cells to gain or lose water by osmosis.
• Hypotonic solutions have lower solute concentrations outside the cell than inside, causing water to enter the cell by osmosis.
• Hypertonic solutions have higher solute concentrations outside the cell than inside, causing water to move out of the cell by osmosis.
• Isotonic solutions have equal concentrations on both sides of the membrane, resulting in no net movement of water across the membrane.
• When a plant is submerged in a very hypotonic solution, the cell will become turgid.
• The movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid requires energy from ATP hydrolysis.
• Membrane potential is the voltage across a membrane.
• Proton pumps are necessary to all cell membranes.
• The movement of potassium into an animal cell through the sodium-potassium pump requires an energy source such as ATP.
• Peripheral proteins are loosely bound to the surface of the membrane.
• Cholesterol is found wedged in between the phospholipids.
• Increasing the percentage of cholesterol in the membrane increases the fluidity of the membrane when it is cold.
• Integral membrane proteins are usually transmembrane proteins.