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).
example of simple diffusion is osmosis. Facilitated diffusion on the other hand is dependant on carrier proteins to transport it across the membrane. Diffusion is essential for many organisms as it is a feature of a number of processes which control and supply vital substances to the body in order for basic survival.