<https://sciencing.com/tetrad-microbiology-21759.html>
<http://schema.org/description>
"Microbiology is the study of life-forms so small that they usually can be viewed only through a microscope. These include bacteria, fungi, algae, viruses and protozoa. Bacteria and viruses are prokaryotic organisms, lacking a nucleus. Algae, fungi and protozoa are eukaryotes that have a nucleus. Structures called tetrads, which means \"groups of four,\" exist in bacteria, fungi, algae and protozoans. The term refers to products of cell division in eukaryotes and of organism division in bacteria."
<https://sciencing.com/tetrad-microbiology-21759.html>