Chapter 44 - Osmoregulation & Excretion

Chapter 44 - Osmoregulation & Excretion - 44.1...

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44.1 Osmoregulation balances the uptake & loss of water & solutes - osmoregulation = regulation of solute & water concentrations in body fluids by organisms living in hyperosmotic, hypoosmotic, & terrestrial environments - Osmosis - Osmosis: movement of water across a selectively permeable membrane - Occurs when 2 solutions differ in osmolarity/osmotic pressure - Isoosmotic: same osmolarity - no net movement of water - 2 solutions that differ in osmolarity: hyperosmotic >>>>>>> hyposmotic higher concentration of solutes lower concentration of solutes - direction of water flow: hypoosmotic ==> hyperosmotic Osmotic Challenges - (marine animals) isoosmotic to the surroundings - ==> osmoconformer = animal that does not actively adjust its internal osmolarity b/c it is isotonic w/its environment - no tendency to gain/lose water - =/=> osmoregulator = animal whose body fluids have a different osmolarity than the environment it lives in - hypotonic environment: discharge excess water - hypertonic environment: take in water - osmoregulation has an energy cost - osmoregulators must expend energy to maintain osmotic gradients - depends on: 1. How different an animal’s osmolarity is from its surroundings 3. How much work is required to pump solutes across the membrane - accounts for ~5% of resting metabolic rate of many marine & freshwater bony fishes - stenohaline = organisms that cannot tolerate substantial changes in external osmolarity - euryhaline = organisms that can survive large fluctuations in external osmolarity Marine Animals - most marine invertebrates are osmoconformers - total osmolarity (sum of the concentrations of all dissolved substances) is the same as that of seawater - differ from seawater in concentrations of most specific solutes
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Chapter 44 - Osmoregulation & Excretion - 44.1...

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