2 concentration is the diffusion of water across a semipermeable membrane 3 What type of tubing is used in this experiment 4 What vegetable is placed in the hypertonic and hypotonic solutions BJECTIVES Understand the concepts and differences between selective permeability active vs passive transport diffusion and osmosis Describe the movement of water across the plasma membrane when a cell is surrounded by a hypotonic hypertonic or isotonic solution Understand the effect of temperature on diffusion rate Understand the effect of solutes complexity or molecular size on the rate of osmosis or membrane permeability respectively NTRODUCTION mportant Terms Solute A substance dissolved in a solution Solvent The liquid in which a solute is dissolved to form a solution Concentration gradient The gradual difference in concentration of a dissolved substance solute in a solution between a region of high density and one of lower density Cells must exchange nutrients wastes and gases with their surroundings The plasma membrane is sometimes called the cell s gatekeeper since it controls the movement of substa into and out of cells The plasma membrane can act as a gatekeeper because of its selective permeability Selective permeability means the membrane will allow some substances to pass across but it will prevent the movement of other substances There are two basic types of movement across the