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 occurs in gases and with any substance in a solution. Therefore we can say that the definition of diffusion is as follows: Diffusion: The movement of particles from an area of high concentration to an area of low concentration until they spread out evenly. There are two important rules to remember. The larger the particles the slower the rate of diffusion. The greater the difference in concentration the greater the rate of diffusion. This difference is known as the concentration gradient. Example of diffusion in plant cells; Example of diffusion in animal cells