Inclusions accumilate when a cell is grown in the presence of excess nutrients and they are often observed under laboratory conditions. It is a long polymer of repeating hydrophobic units that can have various carbon chains attached to them. Some PHA polymers have plastic like qualities and there is some interest in exploiting them as a form of biodegradable plastic. The function of PHA in bacteria is as a carbon and energy storage product. The general structure of a PHA monomer Glycogen Glycogen is another common carbon and energy stroage product.
Humans also synthesize and utilize glycogen.
Glycogen is a polymer of repeating glucose units. Many organisms will accumilate granules of polyphosphate, since this is a limiting nutrient in the environment. The globules are long chains of phosphate. Photosynthetic bacteria that do not evolve oxygen will often use sulfides as their source of electrons, some of them accumilate sulfur globules. These globules may later be further oxidized and disapper if the sulfide pool dries up.