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).
Diffusion is one of the processes that allows this to happen. Diffusion diffusion: The movement of particles (molecules or ions) from an area of higher concentration to an area of lower concentration occurs when particles spread.They move from a region where they are in high concentration to a region where they are in low concentration.he higher concentration of carbon dioxide in the air diffuses into the leaf for photosynthesis. Oxygen produced during photosynthesis builds up to higher concentrations and diffuses out of the leaf into the air which has a lower concentration of oxygen. Page: 1  1. 2  2.