Explain the mechanism of gaseous exchange between tissues and blood.

(N/A) $1$. During cellular respiration, cells consume $O_2$ and produce $CO_2$. This creates a lower partial pressure of $O_2$ and a higher partial pressure of $CO_2$ in the tissues compared to the blood.
$2$. Due to this concentration gradient, $O_2$ diffuses from the blood into the tissues.
$3$. Simultaneously, $CO_2$ diffuses from the tissues into the blood.
$4$. This entire process occurs passively through the mechanism of diffusion.