I think it might be values.
Difussion occurs from a high concentrated region to a low concentrated region. The velocity of diffussion is proportional to the differential of concentrations. In the lung arrives blood with low levels of oxygen while the long is rich with fresh oxygen so the oxygen flows from the lung tissues to the blood.
The other tissues consume oxygen continually them they get poor in oxygen and so the oxygen that is in the blood diffuses to the tissue that is poor in oxygen.
<span>A pathogen exists in the ground air and living thing but does not need them to live or reproduce. It can be a virus, protozoa, parasite, fungus, or bacterium which can cause infection to human. Some pathogens lead to the disease called malaria which is from a bacteria that released toxins in the body. However, our white blood cells can destroy these pathogens.</span>
I don't know if you have this as an answer choice, but it's part of your conscious. Hope this helps some!
