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Lecture Notes Chapter 44

Lecture Notes Chapter 44 - Chapter 44 Osmoregulation and...

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Chapter 44: Osmoregulation and Excretion Osmoregulation Adjustment of the relative concentrations of water and solutes in the internal environment Movement of H2O and solutes Osmosis 1. The physiological systems of animals operate in a fluid environment 2. The relative concentrations of water and solutes in this environment must be maintained within fairly narrow limits Biological membranes are semipermeable o Differential permeability with respect to certain ions, organic substances, gases, and water Excretion Detoxification and elimination of excess or toxic side products of metabolism Phosphorous, nitrogen Osmotic pressure is the hydrostatic pressure produced by a solution divided by a semipermeable membrane due to a differential in the concentrations of solute. Osmoregulation is the homeostasis mechanism of an organism to reach balance in osmotic pressure. Osmolarity is distinct from molarity because it measures moles of solute particles rather than moles of solute. The distinction arises because some compounds can dissociate in solution, whereas others cannot. Multiple compounds may contribute to the osmolarity of a solution. Cells require a balance between osmotic gain and loss of water Movement of water across a selectively permeable membrane Occurs when two solutions separated by membrane differ in osmotic pressure Osmoregulation is a form of homeostasis Solutes (dissolved substance) – Solvent (water) Freshwater animals show adaptations that reduce water uptake and conserve solutes Desert and marine animals face desiccating environments with the potential to quickly deplete the body water Osmoregulation Regulates solute concentrations and balances the gain and loss of water Osmoregulation balances the uptake and loss of water and solutes based largely on controlled movement of solutes between internal fluids and the external environment Osmoconformers are isoosmotic with their surroundings and do not regulate their osmolarity 1
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only marine animals Osmoregulators expend energy to control water uptake and loss hyperosmotic environment – higher salt concentration than the organism hypoosmotic environment – lower salt concentration that the organism o Stenohaline animals cannot tolerate substantial changes in external osmolarity o Euryhaline animals can survive large fluctuations in external osmolarity A. Marine Animals Most marine invertebrates are osmoconformers Most marine vertebrates and some invertebrates are osmoregulators o Marine bony fishes are hypoosmotic to sea water and lose water by osmosis and gain salt by both diffusion and from food they eat o These fishes balance water loss by drinking seawater Freshwater Animals Freshwater animals constantly take in water from their hypoosmotic environment o Lose salts by diffusion Freshwater animals maintain their water balance by excreting large amounts of dilute urine
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