Insects do not have lungs as we do, nor do they breathe

Chapter , Problem 45

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Insects do not have lungs as we do, nor do they breathe through their mouths. Instead, they have a system of tiny tubes, called tracheae, through which oxygen diff uses into their bodies. The tracheae begin at the surface of an insects body and penetrate into the interior. Suppose that a trachea is 1.9 mm long with a cross-sectional area of 2.1 3 1029 m2 . The concentration of oxygen in the air outside the insect is 0.28 kg/m3 , and the diff usion constant is 1.1 3 1025 m2 /s. If the mass per second of oxygen diff using through a trachea is 1.7 3 10212 kg/s, fi nd the oxygen concentration at the interior end of the tube.