1. "For oxygen to enter the blood, how must the concentration of O2 in the alveoli compare to O2 in the blood?" 2. "For carbon dioxide to leave the blood and enter the alveoli, how must the concentration of CO2 in the blood compare to CO2 in the alveoli?" 3. "When diffusion has reached equil- ibrium, we say that the net movement of the molecules is zero. Does movement stop? Explain."

1. Concentration of O2 in the alveoli must be more than that of the blood

2. Concentration of CO2 in the blood must be more than that of the alveoli

3. Movement does not stop (find the explanation below).

Explanation:

Gaseous exchange i.e. taking in of O2 and taking out of CO2, takes place in the alveoli/air sac of the lungs. However, the movement in and out of O2 and CO2 from the alveoli into the bloodstream and vice versa follows the principles of SIMPLE DIFFUSION. Diffusion is the process whereby substances move from a region of high concentration to a region of low concentration until they are evenly distributed. Based on this, the following will occur:

1. The concentration of O2 in the alveoli must be more than that in the blood in order for oxygen to enter the blood via diffusion.

2. The concentration of CO2 in the blood must be more than that in the alveoli in order for carbon dioxide to leave the blood and enter the alveoli via diffusion.

3. When the rate of diffusion is at equilibrium i.e. no net movement is occuring die to equal concentration of the substance on both sides, the substances begin to move in the opposite direction at an equal rate. Note that, at equilibrium, MOVEMENT DOES NOT STOP, however, there is an equal rate of movement.

not only is it colder, it also becomes darker, less salty, and more dense.