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 happens because particles in gases and liquids move about. However diffusion would be greater in gas than in liquid because the particles in a gas move and spread qu â¦ icker and there is more space to move to.iffusion happens because particles in gases and liquids move about. However diffusion would be greater in gas than in liquid because the particles in a gas move and spread qu â¦ icker and there is more space to move to.