Ohio Biology EOC B.DI (Diversity and Classification): classification and taxonomy, phylogeny and cladograms, the domains and kingdoms, biodiversity, and adaptations and niches

What the classification topics demand

The Diversity and Interdependence strand (B.DI) has a classification-and-biodiversity side and an ecology side. This guide covers the classification and biodiversity side: how life is organized and named, how its relationships are displayed, the largest groups, why diversity matters, and how adaptations fit organisms to their roles. (The ecology side, with ecosystems, energy flow, matter cycling, and human impact, is in the ecology and interdependence guide.) The main content statement is B.DI.1 (Biodiversity: genetic and species diversity), supported by B.E.2 (classification expanded to molecular evidence). The recurring crosscutting concepts are patterns and structure and function, and the science practices most in play are developing and using models (reading cladograms) and constructing explanations.

This guide ties together the matching topic pages, each with its own practice questions: classification and taxonomy, phylogeny and cladograms, the domains and kingdoms, biodiversity and its value, and adaptations and niches.

Classification and taxonomy

Organisms are organized into a hierarchy of nested groups: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species (broadest to narrowest). The key rule is that the more levels two organisms share, the more closely related they are: same genus is close, same kingdom is distant. Every species has a two-part scientific name (binomial nomenclature): a capitalized, italicised genus and a lower-case, italicised species, as in Canis lupus. Scientific names are unique and universal, unlike common names. Modern classification groups organisms by shared characteristics and molecular evidence so the groups reflect evolutionary relationships.

Phylogeny and cladograms

A phylogenetic tree or cladogram is a branching diagram of evolutionary history. The tips are species, the nodes are common ancestors, and the rule is that the more recently two species share a node, the more closely related they are; species at the base branch off earliest and are most distant. Judge relatedness by tracing back to the most recent shared branch point, not by how near two tips sit (branches can be rotated). Cladograms are built from shared derived characters: a trait shared by a group indicates a common ancestor, so it groups those species, and the branch point marks where the trait arose. Structural and molecular evidence should agree.

The domains and kingdoms

All life falls into three domains: Bacteria and Archaea (both prokaryotic, single-celled, no nucleus) and Eukarya (all eukaryotes, with a nucleus). The biggest divide is prokaryote versus eukaryote. Within Eukarya are the major kingdoms: Protista (mostly unicellular), Fungi (heterotrophs that absorb nutrients, chitin walls), Plantae (autotrophs that photosynthesise, cellulose walls), and Animalia (heterotrophs that ingest, no walls). Classify by three questions: nucleus? cells? nutrition? Watch the traps that fungi are heterotrophs (not plants) and that cell walls are not unique to plants.

Biodiversity and its value

Biodiversity has two levels in the standards. Genetic diversity (variety of alleles) is a population's insurance: high diversity means some individuals are likely to survive a disease or change, while low genetic diversity makes a population vulnerable because all individuals share the same weaknesses (the monoculture problem). Species diversity (number and abundance of species) supports ecosystem stability, because more species provide backup roles and feeding relationships, making the ecosystem more resilient. Biodiversity arises from evolution (mutation, selection, speciation) and provides humans with food, medicine, and ecosystem services.

Adaptations and niches

An adaptation is an inherited trait that improves survival and reproduction, produced by natural selection. The three kinds are structural (a body part), physiological (an internal process), and behavioral (an action). An organism's habitat is where it lives (its address) and its niche is its role (its job). When species have different niches they use different resources and compete less, so many species coexist, supporting biodiversity; if two species share the exact same niche, the better competitor tends to outcompete the other.

Check your knowledge

A mix of recall and reasoning questions covering the classification topics. Attempt them under timed conditions, then check against the solutions.

1. List the eight levels of the taxonomic hierarchy from broadest to narrowest. (2 marks)
2. State two advantages of a scientific name over a common name. (2 marks)
3. On a cladogram, what does a node represent, and how do you tell which two species are most closely related? (2 marks)
4. Name the three domains of life and state which are prokaryotic. (2 marks)
5. State one characteristic that places a mushroom in kingdom Fungi rather than Plantae. (1 mark)
6. Explain why a monoculture crop with low genetic diversity is at high risk from a new disease. (2 marks)
7. State the difference between genetic diversity and species diversity. (2 marks)
8. State the difference between a habitat and a niche, and explain how different niches let two species coexist. (3 marks)