Diffusion vs. facilitated transport
a. if diffusion was the only mode of oxygen transport, how long would it take for a molecule of oxygen to diffuse from your lungs to the most distal part of your body (toes)? assume d = 2.1 x 10-5 cm2/s and work the problem for 1-d, 2-d and 3-d.
b. compare this diffusion time with the amount of time a red blood cell travels from your heart to your big toe.

To save energy, the air supply to a 2000 ft office has been shut off overnight and the room temperature has dropped to 40°f. in the morning, the thermostat is reset to 70°f and warm air at 120 f begins to flov in at 200ft'/min. the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct. the air pressure is nearly 1 atm everywhere. ignoring heat transfer with the surroundings and kinetic and potential energy effects, estimate how long it takes for the room temperature to reach 70°f. plot the room temperature as a function of time.