Prokaryotic organisms fall into two domains: bacteria and archaea, which contain autotrophs and heterotrophs. Regardless of domain, prokaryotes share common traits of being single-celled organisms that are the smallest and simplest in composition and structure of all organisms. Prokaryotes are further divided into groups within their domains; both groups contain heterotrophs and autotrophs, and a variety of species.
Prokaryotes are divided into two groups depending on how they obtain nutrients, which are autotrophic and heterotrophic methods. Autotrophic prokaryotes are those that obtain food by making it themselves: these organisms primarily use the process of photosynthesis, which involves absorbing sunlight and converting it to usable energy, to produce food. These prokaryotes may also derive energy from inorganic chemicals, and are referred to as chemosynthetic organisms. Cyanobacteria, according to SUNY, are types of prokaryotes that use photosynthesis for food production. While some prokaryotes make their own food for energy, others obtain nutrients by ingesting food particles and organic matter. These organisms, called heterotrophic prokaryotes, are primarily aerobic, and include three distinct species. These types of heterotrophs are: saprotrophic, parasitic and mutualistic organisms. Saprotrophic organisms are decomposers; this group includes the most heterotrophs. Parasites derive food from host species, usually in a predatory manner while mutualistic heterotrophs engage in mutually beneficial relationships with other species to obtain and exchange food and water.