1. List some factors affecting the rate of diffusion of molecules across lipid bilayers: Concentration gradient, Temperature, Pressure 2. What is the difference between a carrier protein and a channel protein? Channel proteins allow that passive diffusion of specific modules down their concentration gradient through a fixed conformational pore, while carrier proteins bind to specific molecules and undergo a conformational change ro transport them across the membrane 3. What is the difference between direct and indirect active transport? Direct active transport uses metabolic energy directly to move molecules against their concentration gradient, while indirect active transport couples the movement of one molecule against its concentration gradient with the movement of another molecule down its concentration gradient 4. Explain the mechanism of the Na+ /K+ pump. The pump binds three intracellular sodium ions (Na+) and one molecule of ATP. The binding of ATP leads to the phosphorylation of the pump at a highly conserved aspartate residue. The phosphorylation of the pump causes a conformational change that releases the sodium ions outside the cell. The pump then binds two extracellular potassium ions (K+). The binding of potassium ions leads to the dephosphorylation of the pump, which returns it to its original conformation.