Ch2 Adaptations to the Physcial Environment - Water and Nutrients6.pdf

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University of Toronto St. George
University College Courses
Spencer Barrett

Water Retention in Marine Animals  hypo-osmotic orgnms are surrounded by water w/ a salt conc. higher than their bodies  tend to lost water, must drink seawater to replace  salts in water and food and by diffusion through body surfaces must be excreted by gills and kidneys  sharks and rays:  retain urea (nitrogenous by-product of protein metabolism in vertebrates) in blood (instead of excreting it)  urea conc. of up to 2.5% (compared to <0.03% in other vertebrates) raise osmotic pot. of blood to the level of seawater w/o any increase in conc. of Na and Cl ions -  thus, the mvmt of water across a shark’s body is balanced (neither gain nor loss)  they don’t have to drink extra salt water to replace water loss by osmosis  but urea impairs protein function  they accumulate high conc. of trimethylamine oxide to protect proteins from –ve effects  freshwater rays don’t accumulate urea Animals Must Excrete Excess Nitrogen without Losing Too Much Water  most carnivores consume excess N 
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