What type of biological organisms are most commonly prokaryotes?

Prokaryotes are unicellular organisms characterized by the absence of a nucleus and membrane-bound organelles. Among the listed organism types, bacteria are the most common prokaryotes. They are found in diverse environments, exhibiting a wide range of metabolic pathways and genetic variations. Bacteria play essential roles in ecosystems, such as decomposers and in some cases, they also have beneficial relationships with higher organisms, including humans, through processes like digestion and nutrient cycling.

In contrast, plants, animals, and fungi are all eukaryotic organisms, which means they contain a nucleus and organelles that are compartmentalized within membranes. This key difference in cellular structure is what categorizes them as eukaryotes, distinguishing them from prokaryotic organisms like bacteria.