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).
What Is Simple Diffusion? In a solution or gas that has an area of high numbers of particles and an area of lower numbers of particles, the particles will diffuse, or move, from the area of higher to the area of lower concentration. This is known as simple diffusion, or passive diffusion. Simple diffusion does not require energy. Instead, it happens by random motion. Random motion is defined as movement that occurs by chance because there is no order or regular system by which the movements of the particles shift in a solution or gas.