Technically a microorganism or microbe is a microscopic organism. ... Microorganisms can be bacteria, fungi, archaea, or protists. The term microorganisms do not include viruses and prions, which are generally classified as non-living. What are cells? Cell structure is classified into two main groups: a spherical structure called a sphere and a columnar structure called a coccoid. The development of cells from a single cell starts with forming a sphere that is embedded within the cytoplasm, which is a fluid inside the cell. A pattern of ribosomes - proteins used in the cell's construction - is developed in the sphere.