4 osmoreg 2010 - 5/4/10 1 Osmoregulation and Excretion...

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Unformatted text preview: 5/4/10 1 Osmoregulation and Excretion Biology 5B Excretion is the disposal of nitrogen containing metabolites and other waste products Osmoregulation regulates solute concentrations and balances the gain and loss of water Freshwater animals show adaptations that reduce water uptake & conserve solutes Desert and marine animals face reduce water loss and avoid excess solutes 5/4/10 2 Osmolarity Cells require a balance between osmotic gain and loss of water Osmolarity , the solute concentration of a solution, determines the movement of water across a selectively permeable membrane If two solutions are isosmotic , the movement of water is equal in both directions If two solutions differ in osmolarity, the net flow of water is from the hyposmotic to the hyperosmotic solution Osmolarity is measured as: # of moles solute L solvent You should think of this as the number of particles that can move in a solution; they give the solution its osmotic potential 5/4/10 3 Concept : Osmoregulation balances the uptake and loss of water and solutes Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external environment Impermeable membrane Selectively Permeable Membrane, permeable only to the red molecules Free diffusion of two different molecules Remember: Solutes will move down their own concentration gradient The concentration of each molecule (color dot) will be the same Water will follow the concentration gradient of particles if possible Osmotic Challenges Only some marine animals are Osmoconformers . They are isosmotic with their surroundings and do not regulate their osmolarity. Euryhaline animals can tolerate a great deal of change Osmoregulators expend energy to control water uptake and loss in a hyperosmotic or hyposmotic environment. Animals that can not tolerate substantial changes are Stenohaline . 5/4/10 4 Marine Animals Most marine invertebrates are osmoconformers Most marine vertebrates are osmoregulators Marine bony fishes are hyposmotic to sea water They lose water by osmosis and gain salt by diffusion and from food They balance water loss by drinking seawater and excreting salts Gain of water and salt ions from food Osmotic water loss through gills and other parts of body surface Excretion of salt ions and small amounts of water in scanty urine from kidneys Gain of water and salt ions from drinking seawater (a) Osmoregulation in a saltwater fish 5/4/10 5 Freshwater Animals Freshwater animals constantly take in water by osmosis from their hyposmotic environment They lose salts by diffusion and maintain water balance by excreting large amounts of dilute urine Salts lost by diffusion are replaced in foods and by uptake across the gills Uptake of water and some ions in food Uptake of salt ions by gills Osmotic water gain through gills and other parts of body surface Excretion of large amounts of water in dilute urine from kidneys (b) Osmoregulation in a freshwater fish...
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4 osmoreg 2010 - 5/4/10 1 Osmoregulation and Excretion...

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