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Unformatted text preview: Osmoregulation and Excretion 1) Osmosis= the movement of water across a selectively permeable membrane. a) Occurs whenever two solutions separated by a membrane differ in osmotic pressure, or osmolarity (moles of solute per liter of solution). b) Isotonic solution contain about as much solute relative to individual cells(solutions have the same osmolarity) no net loss or gain c) Hypertonic solutions contain a higher concentration of solute relative to individual cells. Net water loss, cell shrinks d) Hypotonic solutions contain a lower concentration of solute relative to individual cells. Net water gain, cell swells e) Water flows by osmosis from a hypoosmotic solution to a hyperosmotic one 2) Adaptations for dealing with water a) Marine environments i) Hypertonic for most vertebrates ii) Drink a lot of water iii) Concentrated urine with lots of salt, little water b) Freshwater environments i) hypotonic ii) Freshwater animals constantly gain water by osmosis and lose slates by diffusion because the osmolarity of their internal fluids is much higher than that of their surroundings. iii) Many freshwater animals maintain water balance by excreting large amounts of very diluted urine. c) Terrestrial environments i) Desiccation= the threat of desiccation id a major regulatory problem for terrestrial plants and animals. Humans die if they lose about 12% of their body water. plants and animals....
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- Spring '07