The Main Groups of Microorganisms in Terms of their Structure and Function

Essentially single-celled microorganisms.
Possess a cell wall around the cytoplasm, containing DNA and smaller ribosomes than eukaryotes.
Characterized by their different shapes, including spherical (cocci), rod-shaped (bacilli) and spiral (spirilla).
Replicate swiftly through binary fission.
Some bacteria serve useful functions, such as in fermentation or decomposition, while others can be pathogenic, causing diseases like tuberculosis or strep throat.

Not classified as living organisms but as infectious agents.
Much smaller than bacteria.
Consist of a protein coat (capsid) which surrounds and protects their genetic material—either DNA or RNA.
Needs to infect host cells to reproduce, which they do by injecting their genetic material into the host.
Diseases caused by viruses include the common cold, influenza, and more serious infections like HIV/AIDS or COVID-19.

Range from single-celled yeast to multi-cellular organisms like mushrooms.
Have eukaryotic cells with a nucleus, containing multiple chromosomes, and membrane-bound organelles.
Cell wall consists of chitin, different from the plant cell wall which is made up of cellulose.
Reproduce both sexually and asexually via the production of spores.
Decomposers in the ecosystem, breaking down organic matter. Some fungi can cause diseases (mycoses) such as athlete’s foot or ringworm.

Single-celled eukaryotic organisms.
Lack a cell wall but possess complex structures for movement and predation, such as flagella, cilia, or pseudopodia.
Most protozoa are harmless, but some species can cause diseases in humans. For example, the Plasmodium species cause malaria.

Ranges from single-celled organisms to large seaweeds.
Have eukaryotic cells containing chlorophyll and other pigments for performing photosynthesis.
Have an important role in marine and freshwater ecosystems, producing a significant amount of oxygen and serving as food for many organisms.
Some algae can cause problems when they bloom in large numbers, causing red tides or algal blooms which can harm other aquatic life.