28GasExchange1Spr11postred

28GasExchange1Spr11postred - Gas Exchange: Moving molecules...

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1 Gas Exchange: Moving molecules Mostly O 2 What is the Unity of Gas Exchange? What process? How do we model it? What can we do to increase the rate (Don’t look at your notes!) Gas exchange - Unity of Life Gas exchange – Unity of Life Fick’s First Law Physics expression Flux = per unit area of an organ Alternative physics expression Flow = total capacity of an organ J = " D # C # x Flux ( amount / unit area / unit time ) = - diffusion coefficient J A = " DA # C # x Flow ( amount / unit time ) = - diffusion coefficient (area) ( Δ pp) ( Δ pp/ Δ x)
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2 Gas exchange organs Useful properties The Fick Equation Rate or flow = -D*A* ( Δ pp/ Δ x). Want to maximize Rate Can’t do much about D - depends on the medium and the diffusing molecule A - Large area > large flow Δ pp - Difference in partial pressure > large flux/flow Δ x - Thin boundary > large flux/flow Some constraints - Fick equation applies to the materials you want to exchange by diffusion, and to materials you don’t want to exchange! This is important for homeostasis! Gas exchange - Diversity of Life Most important axes of diversity are: Phylogeny Size Metabolic Rate Medium Gas Exchange Unicellular organisms Favorable scaling relationships Large surface/volume Short diffusion distances Unfavorable scaling relationships Viscosity of water Simple diffusion ____________ Gas Exchange Terrestrial Plants Face a problem. Must . .. conserve ____________ Cuticle Regulate temperature Release O 2 Avoid photorespiration Acquire _____ Photosynthesis C&R 36.10
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3 Gas Exchange Terrestrial Plants Face a problem. A difficult tradeoff, made worse by very unfavorable gradients! pp CO 2 low in atmosphere - small inward gradient pp H 2 0 often low in atmosphere - large outward gradient Transpiration to Photosynthesis ratio H 2 O out/CO 2 in Varies, but often about 600!
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28GasExchange1Spr11postred - Gas Exchange: Moving molecules...

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