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Diffusion, Osmosis, and Algae! Filamentous Algae under normal conditions even distribution of chloroplasts – from cell wall to cell wall Plant cells in salt solution • Cell membranes pull away from the cell wall • Chloroplasts appear to cluster in the center of the cell. Plant cells in distilled water • Space between chloroplasts • Chloroplasts spread out across cell •Small space between adjacent cells. Why these differences in appearance? Osmosis • Water has DIFFUSED into some of these cells making them expand. Water has DIFFUSED out of some of these cells making them shrink. Osmosis • When placed in ISOTONIC, HYPERTONIC, or HYPOTONIC solution, water will diffuse across the cell membrane. • The diffusion of water across a cell membrane is called OSMOSIS. When does diffusion stop? BRIEF REVIEW: • Solutions are mixtures • Particles are evenly distributed throughout the mixture. • The particles are the SOLUTE (solid stuff), the liquid it is mixed in is the SOLVENT (liquid stuff – usually water) Now, Back To Work! ISOTONIC SOLUTIONS • ISO –SAME; TONIC – SOLUTION • Occurs when the concentration of solute (solid) and solvent (liquid) inside and outside the cell are the same. • Cells appear “normal” Solvent 80% Solute 20% Solution = Solvent 80% Solute 20% Cell HYPERTONIC • HYPER – ABOVE; TONIC – SOLUTION • Occurs when the solute concentration in the surrounding solution is higher than the concentration in the cells. • Cells appear to shrivel or shrink. Solvent 80% Solute 20% Solution > Solvent 90% Solute 10% Cell Cell HYPOTONIC • HYPO – LOW; TONIC – SOLUTION • Occurs when the solute concentration in the surrounding solution is lower than the concentration in the cells. • Cells appear to expand. Solvent 90% Solute 10% Solution < Solvent 80% Solute 20% Cell Cell Osmosis • When placed in a HYPERTONIC solution, water moves from inside the cell to the surrounding solution. • It moves from HIGH concentration (inside the cell) to LOW concentration (outside the cell). low low high low same same low Equilibrium reached! Osmosis • When water moves out of a cell, water pressure decreases. • The decrease in pressure allows the cell membrane to pull away from the cell wall. • The organelles appear to cluster in the center of the cell. • This is PLASMOLYSIS. Write a definition for plasmolysis in your own words. Osmosis • When placed in a HYPOTONIC solution, the water moves from the surrounding solution into the cell. • It moves from HIGH concentration (outside the cell) to LOW concentration (inside the cell). high same high same low high high Equilibrium reached! Osmosis What about ISOTONIC solutions? • Molecules are always moving. • Water moves in and out equally. same same Let’s try some practice! Experimental Set ups Demonstrating Osmosis Higher WATER concentration Lower WATER concentration Beaker contains tap water and bag contains 20 % NaCl In the set up does the water in the narrow tube rise, fall down or shows no change? In which direction has the water moved? Is this a Hypertonic, Hypotonic, or Isotonic solution? Water moves from beaker to bag! Beaker and bag contain 20 % NaCl In this set up does the water in the narrow tube rise, fall down, or shows no change? In which direction has the water moved? Net movement of water is the same (going both IN and OUT, therefore overall no Is this a Hypertonic, Hypotonic, or Isotonic solution? movement of water is seen. Higher WATER concentration Lower WATER concentration Beaker contains25 % NaCl and bag contains 20 % NaCl In this set up does the water in the narrow tube rise, fall down or shows no change? In which direction has the water moved? Water moves from bag into Is this a Hypertonic, Hypotonic, beaker or Isotonic solution? On your illustrations from yesterday: • Label the HYPERTONIC solution HYPOTONIC solution ISOTONIC solution • Draw arrows on each illustration to show which direction the water is moving • Label the illustration that shows PLASMOLYSIS