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Lecture 2-Sept 10.docx

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BIOL 2200
Joseph Rasmussen

Sept 10, 2013 Living organisms all interact with the physical world  Do work against it/ use energy to decrease entropy o Move weight against gravity o Transport solute against concentration gradients o Exclude/eliminate waste substances  All living processes take place within limits set by the physical world Energy transfers  Carbon and oxygen play a major role in biological energy transformations  Oxidation means giving up electrons (+)  Reduction means taking on electrons (-)  The oxidation state of C in CO2 is +4, and in carbohydrates is 0.  How many electrons do each C take up during photosynthesis? o Going from +4 to 0, it takes on 4 electrons How to assign oxidation numbers  We keep track of the e- transfer using oxidation numbers (Ox#)  For each e- transferred the Ox# changes by 1  Some rules for oxidation numbers o In free elements Ox#=0 o For ion with one atom Ox#= charge. (H+ = 1) o Ox# of O in most compounds is -2  H2O2- O is -1 o Ox# of H in most compounds is +1 o For complex ion like SO4-2, the net Ox# = charge (Thus S=+6) Water is the primary medium for life  Organisms are mostly water  Take up nutrients from water  Discharge wastes into water  Regulate their water content  Life first evolved in water o Primary limiting factor for terrestrial organisms  Water is of primary importance to human society Water has many unique properties  Liquid at ambient temperatures  Ice floats on water o Allows fish to live underneath ice in winter  Powerful solvent – H-bonding o Can rip elements out of crystals or rock  Stores a lot of heat- high specific heat o Can suck heat out of warm bodied animals- that’s why you get so cold when your in a lake for hours  Seals have lots of fat to store heat away from water  High viscosity- resists deformation, drag o High resistance in water when swimming  High density- buoyancy Dissolved matter  Dissolved matter is taken up by diffusion in aquatic organisms o Very slow process  When the boundary layer becomes stagnant molecular diffusion rates can o Limit algal photosynthesis o Limit animal or microbial metabolism  Tiny algae have high surface/volume ratios to offset slow diffusion in water Hydrogen ions  Play a major role in dissolving minerals from rocks  Most organisms are highly sensitive to the H+ ion  Indicator species can be use to back-calculate pH though history in mud cores  At high pH
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