Bacteria
Bacteria are single-cell organisms that are involved in every level of biological processes and are pervasive through every environment where life is found. Conceptually, the development of cellular biology is the grounds on which all modern vitalism is studied, and is the logical space between the merely physical and the social. Therefore, the discovery of bacteria informs practical sciences such as Agriculture to Health. Additionally, the exploitation of bacteria is the basis of many culinary practices which involve fermentation: beer, bread, cheese, and many more.
Bacteria are all but invisible without the use of sophisticated apparatus such as microscopes. Additionally, the differentia of bacteria are largely even more obscure and can only be discovered by genomic analysis.