What are the four major groups of microorganisms?

Microorganisms are classified into four major groups: bacteria, fungi, protozoa, and some algae. Bacteria are single-celled organisms with diverse shapes and functions. Fungi, including molds and yeasts, are responsible for processes like decomposition and fermentation. Protozoa are single-celled, microscopic organisms often found in water, causing diseases like malaria and dysentery. Some algae, also microorganisms, play crucial roles in ecosystems.
Viruses, though microscopic, are distinct and reproduce only inside host cells, causing common ailments like cold and serious diseases like polio. Understanding these groups is essential in comprehending their varied roles in nature and their impact on human health.