Osmolarity And Tonicity In Cells

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Determination of osmolarity and tonicity of solutions In order to predict whether osmosis will occur when a cell is placed in a solution, two characteristics about the solution need to be determined (in this order): 1st the osmolarity 2nd the tonicity. 1st Determine the osmolarity of the solution the cell is placed in. in order to due this, determine whether the solution has a salt that dissociates into ions and, if so, how many ions per molecule are formed upon dissociation. (e.g. NaCl 1 Na+ and 1 Cl- are formed). Calculate the osmolarity of that solution. What is the molar concentration of ALL particles? e.g. 0.15 M NaCl solution = 0.15 moles of Na+ atoms + 0.15 moles of Cl- atoms = 0.30 Osmoles In other words, the solution is said to have an osmolarity of 0.30 Osm (or 300 mOsm) Assume the osmolarity of the ICF of body cells to be 0.300 Osm (300 mOsm) 2nd, determine if the solute is a PENETRATING particle or is NON-PENETRATING. 3rd, determine whether a concentration gradient of NON-PENETRATING particles exist or not. If a gradient exists, determine where the higher concentration of non-penetrating particles exist; in the ICF or the ECF? (Assume the 300 mOsm concentration of particles in the ICF of body cells is composed of non-penetrating particles) 4th, repeat your definition of osmosis in order to determine if water will move: a. into the cell b. out of the cell c. not move into or out of the cell Osmosis is the diffusion of water across a membrane from a region of lower concentration of non-penetrating particles into a region of higher concentration of non-penetrating

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