Microbe Explorer — the six groups in this chapter
From boiling hot springs to deep beneath Antarctic ice, microorganisms are found almost everywhere, in great quantities. Most are harmless — and many are essential: they form the backbone of food webs, and without them there would be no bread, cheese or beer. The groups differ in size, structure, habitat and metabolism. Some — the viruses — are acellular and do not fall within any of the three domains of life.
Size & Scale — why we need microscopes
An object must measure about 100 µm to be visible without a microscope. For perspective: a typical animal cell is roughly 10 µm across, bacterial cells are typically about 1 µm, and viruses can be 10 times smaller than bacteria. Step through the four levels — and switch between the naked eye and a microscope to see the difference.
History Timeline — from the first ferment to the Golden Age
Humans have been living with — and using — microorganisms for far longer than they have been able to see them. Long before the microscope, doctors, philosophers and writers reasoned about contagion, bad air, sanitation and even immunity. Select an event from the timeline to see what was known — and why it mattered.
Tree of Life — four drafts of the family tree
Taxonomy is the classification, description, identification and naming of living organisms. Carolus Linnaeus published Systema Naturae in 1735; since then the tree of life has been redrawn again and again — ending with the three domains used today, which are based on gene sequences rather than outward appearance. Step through the four drafts.
Where does it belong?
Pick an organism, then choose its place in the modern tree. One of them does not belong to any domain.
Name That Microbe — binomial nomenclature
Linnaeus introduced a two-word naming system — genus + specific epithet — so scientists everywhere could discuss organisms with consistent terminology: the genus is always capitalized, the epithet is not, and both names are italicized (Homo sapiens). Within one species there can be several subtypes called strains. Practice the rules below.
Chapter Quiz — An Invisible World
Fourteen questions covering the whole chapter: the long history before the microscope, taxonomy and nomenclature, the types of microorganisms, and the birth of microbiology as a science.