Biological Diversity
Biological Diversity
This domain tests classification, phylogeny, and the distinguishing features of major groups. Questions ask you to place organisms in domains and kingdoms, interpret cladograms, and compare viruses, bacteria, protists, fungi, plants, and animals. You must use structural and molecular evidence rather than superficial similarity.
Core rules and concepts
- Life is classified into three domains: Bacteria, Archaea, and Eukarya. Eukarya includes protists, fungi, plants, and animals.
- Viruses are not cells and are not classified in the three domains; they require a host to replicate.
- Classification hierarchy: domain, kingdom, phylum, class, order, family, genus, species. Scientific names use genus and species.
- Phylogenies use shared derived characters. Homologous structures indicate common ancestry; analogous structures indicate convergent evolution.
- Bacteria are prokaryotic; Archaea differ in cell wall and membrane chemistry; protists are a paraphyletic assemblage; fungi are absorptive heterotrophs with chitin cell walls; plants are photosynthetic; animals are multicellular heterotrophs without cell walls.
Worked example
An organism is unicellular, lacks a nucleus, has peptidoglycan in its cell wall, and reproduces by binary fission. It is placed in domain Bacteria. The absence of a nucleus rules out Eukarya; peptidoglycan is a bacterial cell wall marker that separates Bacteria from Archaea. Binary fission is common in prokaryotes but not diagnostic by itself. The reasoning depends on cell structure and cell wall chemistry, not on habitat or shape alone.
Traps that cost marks
- Calling viruses living cells or placing them in a domain.
- Assuming all bacteria are pathogens.
- Treating protists as a single kingdom with one evolutionary lineage.
- Using analogous structures as evidence of close common ancestry.