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Movement of Substances Osmosis Learning outcomes After completing this chapter, you will able to : • Define osmosis as the passage of water molecules from a region of their higher concentration to a region of their lower concentration through a partially permeable membrane • Describe the importance of water potential gradient in the uptake of water by plants and its effect on plant and animals tissues Special Kind of Diffusion Diffusion • Move from HIGH to LOW concentration – “passive transport” – no energy needed diffusion movement of water osmosis Osmosis : Passive Transport • Osmosis: diffusion of water through a selectively permeable membrane • Water moves from high to low concentrations •Water moves freely through pores. •Solute (green) to large to move across. Channels through cell membrane • Membrane becomes semi-permeable with protein channels – specific channels allow specific material across cell membrane inside cell NH3 H2O salt aa sugar outside cell Solution Solutions are made of solute and a solvent (water) Solute - substance that is dissolved or put into the solvent. Salt and sucrose are solutes. DIFFUSION Solvent - the liquid into which the solute is poured and dissolved. We will use water as our solvent today. Osmosis DILUTE SOLUTION CONCENTRATED SOLUTION Cell membrane partially permeable. Sugar molecule VERY Low conc. of water molecules. Low water potential. VERY High conc. of water molecules. Higher water potential. Inside cell Outside cell Osmosis Cell membrane partially permeable. OSMOSIS High conc. of water molecules. High water potential. Inside cell Low conc. of water molecules. Low water potential. Outside cell Osmosis Cell membrane partially permeable. OSMOSIS Inside cell Outside cell Concentration of water • Direction of osmosis is determined by comparing total solute concentrations – Hypertonic - more solute, less solvent (water) – Hypotonic - less solute, mores solvent (water) – Isotonic - equal solute, equal solvent (water) water hypotonic hypertonic net movement of water =solute = solvent Effect of Water on Cells • Hypertonic Environment – High [solute], low [water] • Hypotonic Environment – High [water], low [solute] Hypertonic • Isotonic Environment – [water] = [solute] Hypotonic Isotonic Osmosis in Sugar Solution 5% sugar solution ENVIRONMENT CELL 5 % sugar solution What is the direction of water movement? equilibrium The cell is at _______________. NO NET MOVEMENT Osmosis in Sugar Solution Water CELL 10 % sugar solution What is the direction of water movement? Osmosis in Sugar Solution 10 % sygar solution ENVIRONMENT CELL Water What is the direction of water movement? Animals and Plant Cells in Isotonic Solution Isotonic Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium) Animals and Plant Cell in High Water Potential Hypotonic Solution Hypotonic Turgid Lyses Result: Water moves from the solution to inside the cell): Cell Swells and bursts open Animals and Plant Cell in Low Water Potentials Hypertonic Crenates Plasmolysis shrinks Result: Water moves from inside the cell into the solution: Cell shrinks Managing water balance • Cell survival depends on balancing water uptake & loss freshwater DIFFUSION balanced saltwater Osmosis… .05 M .03 M Cell (compared to beaker) hypertonic or hypotonic Beaker (compared to cell) hypertonic or hypotonic Which way does the water flow? in or out of cell Summary • Osmosis is Diffusion of water across a selectively permeable membrane. • Occurs until water is balanced on both sides of the membrane. Weeee!!! high low What type of solution are these cells in? A Hypertonic B Isotonic C Hypotonic
