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Experiment - AP Biology Osmosis Lab

             Cells are able to move through selective permeable cellular membranes. They must regulate moving necessary materials in and out of the cell in order to maintain homeostasis. Because of a cell's aqueous environment, it allows water to pass by osmosis or aquaporins. With osmosis, water can move throughout the membranes of a cell, down its concentration gradient. Water moves from areas of high potential and low solute concentration to areas of low potential and high solute concentrations. Diffusion is known as the simplest form of movement, where solutes spread from a high concentration area to a low concentration. This process requires no energy, but the movement of a low concentration to a high concentration requires energy by ATP. Since water molecules surround solute molecules, solutes decrease the concentration of free water. To describe the solutions separated by selectively permeable membranes, there are three terms: hypertonic (higher solute concentration and a lower water potential as compared to the other solution), hypotonic (lower solute concentration and a higher water potential than the other solution), and isotonic (equal water parts). .
             Part I. Agar Lab.
             Purpose: This lab is all about finding out if there is a correlation between "cell " size/surface area, and diffusion rates.
             Hypothesis: Cells with a larger surface area to volume ratio are more efficient with diffusion because there is more surface area to absorb the solute with a smaller volume to diffuse into. More solutes enter the cell with a larger surface area to volume ratio.
             - 2% agar containing NaOH and the pH-indicator dye phenolphthalein.
             - 1% phenolphthalein solution.
             - 0.1M HCl.
             - 0.1 M NaOH.
             - Squares of hard, thin plastic (from disposable plates); non-serrated knives; or scalpels from dissection kits.
             - Metric rulers.
             - Petri dishes and test tubes.
             - 2% agar with phenolphthalein .
             1. Place some phenolphthalein in two test tubes.

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