BI110 Lecture Notes - Lecture 18: Facilitated Diffusion, Active Transport, Atp Hydrolysis
Document Summary
Net diffusion of water molecules across a selectively permeable membrane by diffusion. In response to differences in concentration of solute molecules. Selectively permeable membrane must allow water molecules to pass but not solute molecules. Moves from low solute concentration to high solute concentration. Solute concentration determines the rate of diffusion. Solute can be anything that can be dissolved in water. From hypotonic solution (lower concentrations of solute molecules), to hypertonic solution (higher concentrations of solute molecules. Solutions on each side are isotonic when the concentration is same on both sides. No osmotic movement of water in either direction. Active transport requires direct/indirect input of energy derived from atp hydrolysis (or another source of energy) Moves substances against their concentration gradients; requires cells to expend energy. Facilitated diffusion also depends on membrane transport proteins. The same protein that transports substance also hydrolyzes atp to power transport directly. Instead use a favourable concentration gradient of substance as their energy source.