The Black Death was an epidemic of bubonic plague, a disease caused by the bacterium Yersinia pestis that circulates among wild rodents where they live in great numbers and density. Such an area is called a âplague focusâ or a âplague reservoirâ.
Diffusion is the net movement of molecules or atoms from a region of high concentration to a region of low concentration.his is also referred to as the movement of a substance down a concentration gradient. A gradient is the change in the value of a quantity (e.g., concentration, pressure, temperature) with the change in another variable (usually distance).
The three types of diffusion in an independent cell are simple  diffusion, facilitated, and active. The function of simple  diffusion is to transfer oxygen. Facilitated diff â¦ usion transports  water or non polar molecules.Active diffusion transports materials  against the concentration gradient.he function of simple  diffusion is to transfer oxygen. Facilitated diff â¦ usion transports  water or non polar molecules.