When comparing bacteria, fungi, protozoa, and algae, the largest organism typically belongs to the fungi group. Specifically, the Armillaria ostoyae, commonly known as the honey fungus, holds the record as one of the largest living organisms on Earth. This fungus can cover thousands of acres of land through its extensive mycelial network, which can be found beneath the soil.
On the other end of the spectrum, bacteria are generally considered the smallest organisms. Among bacteria, the genus Mycoplasma includes some of the smallest known cells, measuring approximately 0.2 to 0.3 micrometers in diameter. These tiny organisms can thrive in various environments and are often characterized by their lack of a cell wall, allowing them to adopt different shapes.
In summary, the largest organism is the honey fungus (a type of fungus), while the smallest is typically represented by bacteria, particularly those in the Mycoplasma genus.