Ch3 Adaptations to the Physical Environment6.pdf

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University of Toronto St. George
University College Courses
Spencer Barrett

Cold Temperatures and Freezing  temp. below freezing point of water are very common on earth  when living cells freeze, the crystal structure of ice disrupts most life processes and may damage delicate cell structures  many organisms cope by maintaining their body temp., or by activating chemical mechanisms to tolerate or resist freezing  marine vertebrates are susceptible to freezing in cold seawater (how does blood and body tissues freeze solid in liquid water?)  dissolved substances in seawater depress the freezing temp.  pure water freezes at 0°C, seawater, -2°C  vertebrates contain less salt content than seawater, freezing at higher temp. than it  fish can’t keep high salt conc. in their bodies because it interferes with biochemical processes  instead, they raise their conc. of compounds like glycerol (and glycoproteins)  10% glycerol solution lowers freezing point of water by 2.3°C  some terrestrial animals also use this approach (containing as much as 30%)  supercooling:  sometimes, liquids can cool below freezing point w/o ice crystals developing  ice generally forms around some object (called a seed; a small ice crystal or other particle); in the absence of seeds, pure water may cool more than 20°C w/o freezing  such supercooling has been recorded to -8°C in reptiles and -18°C in invertebrates  glycoproteins coat developing crys
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