3.08.10 - Gas exchange systems and gas transport All...

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Gas exchange systems and gas transport All animals must exchange oxygen and carbon dioxide with their environments. Several physical and biological principles are universally important: All animals (aquatic or terrestrial) use these gases in a dissolved state. Movement of gases across membranes is by diffusion (no active transport of gases). The rate of diffusion depends on: -- the diffusion distance (rate ~ 1/distance 2 ) -- the area for diffusion (rate ~ area) -- the concentration gradient (rate ~ gradient) Diffusion is much faster in air than in water, and… Air contains much more oxygen per liter (about 210 ml of O 2 /liter) than does water (5-10 ml of dissolved O 2 /liter at most ) Gas exchange organs heart Systemic circulation Gas exchange organ Gas exchange without specialized exchange organs is possible in animals that are small, thin, and have low MR. • can manage by diffusion across skin For larger, more active animals, cells are too far from the surface for diffusion to be fast enough. Solution: gas exchange organs, usually connected to the circulatory system ( bulk flow much faster than diffusion) Gas exchange organs Gas exchange without specialized exchange organs is possible in animals that are small, thin, and have low MR. • can manage by diffusion across skin For larger, more active animals, cells are too far from the surface for diffusion to be fast enough. Solution: gas exchange organs, usually connected to the circulatory system ( bulk flow much faster than diffusion) Gas exchange organs: are moist (even in air-breathers) have large surface area are thin (to reduce diffusion distance) usually are ventilated (by breathing) -- keeps concentration gradients across surface high Gas exchange organs Tracheole (cuticle) fluid cells Tracheal systems (insects) Network of hollow, air-filled tubes inside the cuticle, collected to the outside through spiracles (controllable) primarily diffusion -- but through gas , not liquid (faster) trachae & tracheoles near every cell in the body diffusion alone OK for small, inactive insects large, active insects ventilate tracheal system
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Gas exchange organs Aquatic animals usually exchange gases through gills: lots of surface area extensive blood supply usually, must be actively ventilated -- O 2 content low in water; need to keep water near exchange surface refreshed -- water is heavy and viscous: expensive to pump (especially since O 2 content low) -- selection to maximize efficiency of exchange (amount of O 2 extracted from breathed water) Gas exchange organs: fish gills Opercula (gill protectors; gills are inside the mouth cavity Fish often ventilate gills by forcefully opening and closing the mouth and opercula.
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This note was uploaded on 04/03/2010 for the course BIO Bio 5b taught by Professor Chappel/douhan during the Winter '10 term at UC Riverside.

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3.08.10 - Gas exchange systems and gas transport All...

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