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Principles of Osmoregulation: Water Balance and Solute summarized lectures notes along with relevant pictures and notes from the assigned readings

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Biology 2601A/B
Brent Sinclair

Organismal Lecture 19 Principles of Osmoregulation: Water Balance 1  Osmoregulation: Balancing water and ions in both the cells and the body to allow physiological function Osmolarity/ Osmolality  The amount of “stuff”/solutes in a solution  1 mol of solutes = 1 Osmole  This measurement is cumulative: 0.2 M of 5 things = 1 Osmole  Osmolality = per kg of solvent  Osmolarity = per Litre of solvent Water Properties  Highly polar o Involved in hydrogen bonding o Has a large dielectric constant (large ratio of the permittivity of a substance to the permittivity of free space) o High heat of fusion and vaporisation o Large thermal capacity (takes lots of energy to heat H₂O from one temp to another) o Has cohesion and adhesion (essential to maintain the continuous water column)  Allows proteins to fold, involved in the lipid bilayer Water Interacts with Other Molecules  Can interact with cations and anions  Water molecules hydrogen bind to the protein; this mean the water is not active (can’t interact with other components of the protein)  Keeps ions dissociated (the amount of ions dissociated in a water solution is very high Water in Cells  Regulates pressure  Determines the cell volume in animals o Cell volume is often the bottom level of regulation of water and ion balance  Determines the cell turgor in plants Comparison of Plant and Animal Cells at High and Low Concentrations  Remember that hypoosmotic means that there is more solutes and less water on the inside of the cells; water will move into cells, causing them to burst  Isosmotic means the same amount of water and solutes in both the cell and environment  Hyperosmotic concentration means there is more solutes and less water outside the cells, causing water to move of of the cell ; the cell then shrinks  In comparison to this, in plants, the pressure of the vacuole will control the amount of water flowing in o Since the vacuole has a rigid cell wall, it will not burst in hypoosmotic conditions o Plasmolysis: the process of the cell shrinking and moving away from the cell wall (hyperosmotic situation) Moving Water: Diffusion  Between the 2 solutions is a perforated barrier with holes in it  Shows the diffusion of solutes into a low concentrated area  Note: the pressure remains the same Moving Water: Osmosis  these 2 solutions are separated by a semi-permeable membrane  The membrane is permeable only to water; solutes are unable to diffuse through the membrane  Water will move into the container with the higher solute enclosure (to the left) o This movement causes osmotic pressure Water Can’t Be Moved Actively  There are no ‘active water transporters’ through the cell membrane  Cell has to set up an osmotic gradient that the water can follow  Aquaporins allow water to pass rapidly, but passively, through the membrane Moving Water Requires the Creation of a Gradient  The cytosol of the cell will actively take up nitrates and move them into the cell  Water will follow due to the gradient created by the NO₃  As well, the more subunits of glucose the animal can break down into glycogen and glucose 1-phosphate, the higher the osmotic pressure becomes o (relate this concept back to cold tolerance)  In some ion pumps, the pump only works in one directio
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