Biological Diversity and Classification
What to know
Classification organizes life by evolutionary relationships. Understand the hierarchy - domain, kingdom, phylum, class, order, family, genus, species - and that binomial nomenclature uses genus and species (italicized or underlined, genus capitalized). Know the three domains (Bacteria, Archaea, Eukarya) and the major eukaryotic kingdoms (Protista, Fungi, Plantae, Animalia) with distinguishing traits: cell type, cell wall composition, nutrition (autotroph vs. heterotroph), and body organization.
Compare major groups: bacteria (prokaryotic, peptidoglycan walls), archaea (prokaryotic, distinct biochemistry, extreme environments), protists (mostly unicellular eukaryotes), fungi (heterotrophic, chitin walls, absorptive nutrition), plants (multicellular autotrophs, cellulose walls, photosynthesis), and animals (multicellular heterotrophs, no cell walls, most with tissues and motility). Know vertebrate classes and their traits (fish, amphibians, reptiles, birds, mammals) and key invertebrate groups. Understand that classification reflects phylogeny, using shared derived characters, and that molecular data have reshaped traditional groupings. Recognize dichotomous keys as tools for identification.
Traps
- Fungi are not plants. They are heterotrophic and have chitin walls.
- Protista is not a clean clade. It is a convenience grouping of mostly unicellular eukaryotes.
- Bacteria vs. archaea. Both are prokaryotic, but they differ in cell wall and biochemistry.
- Species names. Only the genus is capitalized; both parts are italicized.
Rule of thumb
Classify by asking: prokaryote or eukaryote? Then cell wall? Then nutrition? These three questions separate most major groups.
Worked example
An organism is multicellular, has cellulose cell walls, and photosynthesizes. Prokaryote is ruled out; heterotroph is ruled out; cellulose walls and photosynthesis indicate a plant rather than a fungus (chitin, heterotrophic).