Exercise 3: Membranes

OutsidePolar hydrophilicheadsNonpolar hydrophobictailsInsideBPolar hydrophilicheadsAFigure 2. A. Fluid Mosaic model of the Cell Membrane B. General Structure of the PhospholipidBilayer1. What determines the flow of water through the membrane?Task 1 - OSMOSIS AND CONCENTRATION GRADIENTSOsmosis is the diffusion of water across a selectively permeable membrane. Osmosis follows thesame laws as diffusion but always refers to water, the principal solvent in cells. A solution is ahomogenous mixture of two or more substances. In a solution, the solvent is the fluid while the solute isthe substance being dissolved in the solvent.Osmosis (Fig. 3) can be simulated using dialysis bags to model cells in different environments,i.e., under hypo-, hyper and isotonic conditions. The terms hypo-, hyper- or isotonic are always relative tothe concentration of the solutes outside.The exercise that follows will allow you to learn about the properties of osmosis in relation toconcentration of solutions.Concentration Hypotonic Isotonic HypertonicSolute inside Low Same HighSolute outside High Same LowTable 1. Osmosis2