Insects do not have lungs as we do, nor do they breathe through their mouths. In
ID: 306472 • Letter: I
Question
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 diffuses into their bodies. The tracheae begin at the surface of the insect's body and penetrate into the interior. Suppose that a tracheae is 1.45 mm long with a cross-sectional area of 1.94 x 10-9m2. The concentration of oxygen in the air outside the insect is 0.685 kg/m3, and the diffusion constant is 1.72 x 10-5 m2/s. If the mass per second of oxygen is diffusing through a trachea is 1.34 x 10-12 kg/s, then find the oxygen concentration at the interior end of the tube.
Explanation / Answer
The density of blood inside will be:
rho-i = rho-o - dm/dt x L/AD
rho-i = 0.685 - 1.34 x 10^-12 x 1.45 x 10^-3/(1.94 x 10^-9 x 1.72 x 10^-5) = 0.627 kg/m^3
Hence, rho-i = 0.627 kg/m^3