without diffusion how would we not be able to breathe?

Answer 1

We would still be able to breathe air in and out of our lungs, but we would not be able to exchange gases while the air is in our lungs. The oxygen from the air has to diffuse through the walls of the alveoli (little air sacs) and into the capillaries ... and into the red blood cells. The carbon dioxide has to diffuse in the reverse direction.