What term refers to a parasitic particle that infects and resides in the cells of biological organisms?

The term that refers to a parasitic particle that infects and resides in the cells of biological organisms is a virus. Viruses are unique in that they cannot replicate or carry out metabolic processes on their own; they require a host cell to reproduce and to carry out their life cycle. Once inside a host cell, a virus takes over the cell's machinery to produce new virus particles, which can then go on to infect other cells.

Bacteria, on the other hand, are single-celled organisms that can live independently and often reproduce on their own. They can be beneficial or harmful but do not typically reside inside the host cells the way viruses do. Fungus consists of various organisms, including yeasts and molds, which also do not require host cells for their life cycle. Lastly, protozoa are single-celled organisms that can be free-living or parasitic, but they are much larger and more complex than viruses and often do not inhabit cells to the same extent.