Tonicity and Osmoregulation

• Solute 


  The minor component in a solution, dissolved in the solvent
• Osmosis


  The net movement of a solvent through a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration
• Solvent


  The major component in a solution, what the solute is dissolved in
• The best explanation for why the solvent moves from low to high concentration is that the solute molecules bounce against the membrane, knocking away the solvent and making it less likely to cross
• Osmosis visualization

  
• Osmolarity


  Total particles per litre of a solution (concentration)
• Hyperosmotic


  The solution with higher osmolarity
• Hypoosmotic


  The solution with lower osmolarity
• Isoosmotic


  When two solutions have the same osmolarity
• Tonicity


  The ability of an extracellular solution to make solvent move in or out of a cell (factoring in relative concentrations but also the cell membrane's permeability to the solutes)
• Hypertonic


  Solution that causes a net flow of water out of a cell when placed in it (A solution will be this if it has a higher solute concentration than that of the cell and the solute can't cross the membrane)
• Hypotonic


  Solution causing a net flow of water into a cell when placed in it (when it has less solute than the cell and the solute can’t cross membrane) so the volume of the cell increases
• Isotonic


  Solution causing zero net flow of water into or out of a cell when placed in it (because of equal amounts of solvent between the two) so the cell stays the same size
• Turgor


  Pressure exerted by cell fluid pressing membrane against the cell wall
• Plasmolysis


  When there's not enough water in a plant cell because of hypertonic conditions, so the cytoplasm shrivels up and the membrane detaches from the cell wall
• Contractile vacuole


  Specialized vacuole in organisms without cell walls living in hypo or hypertonic environments like amoebas or paramecia that lets them pump water to change their size to keep from lysing
• Lysing

  A cell bursting because it's too full of water