Why is ventilation needed in Humans.

This photo of a mayfly larva shows how oxygen gets into the cells of the mayfly's body.

What gas diffuses into the gills from the water?

What diffuses out of the gills into the water?

How does the wafting of the gills affect the concentration gradient between the oxygen in the water and the oxygen dissolved in the blood inside the gills?

These are the gills of a fish How does a fish maintain a large concentration gradient?	Humans are able to live on land because they have "internal gas exchange surfaces" in the form of lungs.
What would happen to the concentration of CO2 in the alveoli if the air in the lungs never moved? How would the rate of diffusion of CO2 out of the blood change if the air in the lungs didn't move? Describe the change in the rate of diffusion of oxygen into the blood capillaries if you hold your breath. Why is it necessary to ventilate the lungs?