Final answer:
Pleomorphic bacteria are bacteria that show variation in size and shape as a result of environmental conditions or age of the organisms.
Step-by-step explanation:
Bacteria that show variation in size and shape as a result of environmental conditions or age of the organisms are referred to as pleomorphic bacteria. Pleomorphic bacteria are characterized by their ability to change their shape and size in response to their environment or as they age. This variation in shape and size can be observed under a microscope.