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).
active transport requires the usage of energy in the form of ATP to  move something against is concentration gradient. Facilitated  diffusion is a form of simple diffusion i â¦ n that the substance moves  along with its concentration gradient, but it requires the use of a  transport protein.