2-25 respiratory systems I

2-25 respiratory systems I - RESPIRATORY SYSTEMS, PART I...

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RESPIRATORY SYSTEMS, PART I LIFE 48 – 48.3 48.1 What physical factors govern respiratory gas exchange? - respiratory gases that animals must exchange are oxygen (O 2 ) and carbon dioxide (CO 2 ) - Diffusion is the only means by which respiratory gases are exchanged between the internal body fluids of an animal and the outside medium 48.1.1 Diffusion is driven by concentration differences -Because diffusion results from the random motion of molecules , the net movement of a molecule is always down its concentration gradient. One way biologists express the concentrations of different gases in a mixture is by the partial pressures of those gases 48.1.2 Fick’s law applies to all systems of gas exchange - Fick’s law of diffusion : -where Q = rate at which a gas such as O 2 diffuses between two locations. D = diffusion coefficient (constant) A = cross-sectional area through which the gas is diffusing. P 1 and P 2 = partial pressures of the gas at the two locations. L = path length, or distance, between the two locations. Therefore, ( P 1 P 2 )/ L is a partial pressure gradient 48.1.3 Air is a better respiratory medium than water -slow rate of O 2 diffusion in water limits the efficiency of O 2 distribution from gas exchange surfaces to the sites of cellular respiration even in air-breathing animals -Therefore, there are severe size and shape limits on the many species of invertebrates that lack internal systems for distributing O 2 . Most of these species are very small, but some have grown larger by evolving
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2-25 respiratory systems I - RESPIRATORY SYSTEMS, PART I...

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