celltransport-avcdistance…细胞运输-avc的距离…-精选文档.ppt

Transport Across Plasma Membranes (Diffusion and Osmosis) ? The cells inner pool is called: Intracellular fluid. ? In a multicellular organism, the fluid outside the cell is extracellular fluid. ? Movement between fluid compartments are governed in part by gradients, differences in the concentration of materials in one part compared to those in another. Two Kinds of Transport: ? 1. Passive (Diffusion): materials move from regions of higher concentration to regions of lower concentration, without energy expenditure by the cell. ? 2. Active: movement of substances against concentration gradients (from low to high), requiring the expenditure of energy by the cell. Passive Transport and the Movement of Water (Osmosis) Water moves from a region of higher water concentration to a region of lower water concentration. Solution ( Solute and Solvent ) ? Solute: a substance that has been dissolved in a solvent. ? Solvent: a substance capable of dissolving other molecules. Solutions can be: ? Isotonic: two solutions having the same concentration of solutes. ? Cells placed in isotonic solutions maintain their shapes. ? Hypotonic: having a lower concentration of solutes than another solution. ? Cells swell in hypotonic solutions. ? Hypertonic: having a higher concentration of solutes than another solution. ? Cells shrink in hypertonic solutions.