Biol172_Chapter44_handout

Biol172_Chapter44_handout - Osmoregulation and Excretion...

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1 Osmoregulation and Excretion are distinct processes that are often coupled in the same system Osmoregulation Regulates solute concentrations and balances the gain and loss of water Excretion Detoxification and elimination of excess or toxic side products of metabolism Phosphorous, nitrogen Osmoregulation The physiological systems of animals operates in a fluid environment The relative concentrations of water and solutes in this environment must be maintained within fairly narrow limits Osmoregulation is a form of homeostasis Movement of water across a selectively permeable membrane Occurs when two solutions separated by membrane differ in osmotic pressure Osmosis H 2 O Osmotic pressure and osmolarity Osmolarity Moles of solute per liter of solution (Osm/L) Osmolarity measures moles of solute particles rather than moles of solute. The distinction arises because some compounds can dissociate For undissociated solutes osmolarity equals molarity Multiple compounds contribute to the osmolarity of a solution. Osmotic pressure and osmolarity Relative Osmolarity Measured in reference to the internal osmolarity of a cell Isoosmotic Hyperosmotic Hypoosmotic Osmotic pressure and cell behavior Hyperosmotic Isosomotic Hypoosmotic
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2 Osmotic Challenges Freshwater animals Show adaptations that reduce water uptake and conserve solutes Desert and marine animals face desiccating environments potential to quickly deplete the body water Osmoregulation Osmoconformers are isoosmotic with their surroundings and do not regulate their osmolarity only marine animals Osmoregulators expend energy to control water uptake and loss In a hyperosmotic or hypoosmotic environment Osmotic Challenges Marine Animals Most marine invertebrates are osmoconformers Most marine vertebrates are osmoregulators Osmotic Challenges Stenohaline animals cannot tolerate substantial changes in external osmolarity Euryhaline animals can survive large fluctuations in external osmolarity Marine bony fishes are hypoosmotic to sea water lose water by osmosis and gain salt by both diffusion and from food they eat These fishes balance water loss by drinking seawater H 2 O H 2 O NaCl Osmoregulation in Saltwater Fishes Gain of water and salt ions from food and by drinking seawater Osmotic water loss through gills and other parts of body surface Excretion of salt ions from gills Excretion of salt ions and small amounts of water in scanty urine from kidneys
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3 Freshwater animals Constantly take in water from their hypoosmotic environment Lose salts by diffusion Freshwater Animals H 2 O H 2 O NaCl Freshwater animals maintain water balance by excreting large amounts of dilute urine Salts lost by diffusion Are replaced by foods and uptake across the gills Osmoregulation in a freshwater fish Uptake of water and some ions in food Osmotic water gain
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Biol172_Chapter44_handout - Osmoregulation and Excretion...

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