Osmosis and Diffusion Lab - Osmosis and Diffusion Lab...

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Osmosis and Diffusion Lab Jennie Chang Period 6 AP Biology 10/31/11
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Background Information: All molecules in gases and liquids are in constant states of random motion. When molecules are closely packed, they hit each other, bounce off each other, and move away from the point of collision. As a result, the molecules tend to distribute evenly until they reach dynamic equilibrium; individual molecules still move, but in a fashion where so many molecules move in one direction as they do in the opposite direction. Movement from a higher concentration to a lower concentration is known as diffusion. Diffusion also occurs in water separated by a semipermeable membrane but this process is called osmosis. In osmosis, water molecules move from regions of low concentration to regions of high concentration and thus evening out the concentrations toward equilibrium. Only a solute’s water potential affects the rate of osmosis; the size of the solute molecules doesn’t matter. The higher the concentration of solutes, the faster water will flow through the membrane to equalize the concentration because of the higher water potential of the solution. Diffusion is vital to many life functions of a cell because it allows the transport of important nutrients and compounds without having to use any extra metabolic energy. Diffusion is also responsible for the transport and exchange of oxygen and carbon dioxide in the lungs. If a cell is hypertonic to its surroundings, water rushes into the cell, causing it to expand; if that happens in an animal cell, the cell bursts, or cytolizes. If a cell is hypotonic to its surroundings, it loses water and shrinks; this is called plasmolysis. Water potential determines the direction and rate of osmosis. It consists of two components: pressure potential, which is the exertion of pressure on a solution, and osmotic potential, which is the relative concentration of solutes within the two solutions. When the force of gravity(pressure potential) is equal to osmotic potential, water stops entering the tube. The water potential is then at zero and an equilibrium is established. The pressure and water potential can easily be determined with these equations: Water Potential (Ψ) = Pressure Potential (Ψp) + Osmotic Potential (Ψπ). The water potential of a solution is determined by calculating the osmotic potential when the pressure potential is zero. Ψ = Ψp + Ψπ; if Ψp = 0, then Ψ = Ψπ Purpose: The purpose of this lab is to investigate the processes of diffusion and osmosis as well as to investigate the effect of solute concentration on water potential as it relates to plant tissues Materials:
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