Classification & Taxonomy — Quick Reference

Hydra & Classification

  • Hydra: small freshwater animal; can bud to reproduce; used to introduce classification.

  • Question: what makes something an animal vs. plant, protist, or fungus? Leads to taxonomy and classification.

Taxonomy and Classification Basics

  • Taxonomy = naming and classification of species.

  • Carl Linnaeus(start): formal classification beginnings; in the 18th century there was limited knowledge (no DNA, no detailed cell differences).

  • As we learn more (especially DNA), classifications can change to reflect relatedness.

Domains

  • There are three domains: 33 domains: bacteria, archaea, and eukarya.

  • Bacteria: prokaryotes with diverse roles (pathogens, digestion, decomposition, nitrogen fixation).

  • Archaea: prokaryotes with distinct DNA/structure; many extremophiles; some resemble eukaryotes more closely in DNA; many live in extreme conditions.

  • Eukarya: eukaryotes with defined nucleus and organelles.

Why the Domain Concept Matters

  • Separate domains (Bacteria, Archaea, Eukarya) reflect major cellular and genetic differences.

Kingdoms (and How They Change)

  • Historically: five-kingdom system; some systems use six kingdoms.

  • Protista: extremely diverse; includes animal-like, plant-like, and fungus-like protists; many are autotrophs or heterotrophs; mostly unicellular, some multicellular; varying cell walls (cellulose in some).

  • Fungi: heterotrophs; no photosynthesis; usually multicellular (some unicellular); cell walls of chitin.

  • Plantae: autotrophs; multicellular; cellulose cell walls.

  • Animalia: mostly multicellular; heterotrophs.

  • Note: classification systems are evolving with new DNA/cell-structure evidence.

Taxonomic Hierarchy (Less Inclusive to More Specific)

  • Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species

  • Species is the most specific level.

Binomial Nomenclature

  • Scientific name = two-part name: Genus + specific epithet.

  • Genus: capitalized, written in italics.

  • Specific epithet: lowercase, written in italics.

  • Rooted in Latin/Greek roots.

  • Purpose: standardized name across regions to avoid confusion from common names.

Why Scientific Names Matter

  • Common names vary by location; scientific names remain standardized and unambiguous.

Mnemonic (example from the material)

  • Dear King Paramecium cares only for green Spirulina (illustrative mnemonic to recall the order of taxonomic groups).

Hydra in Context

  • Hydra is in the kingdom Animalia; taxonomy demonstrates how we categorize organisms as we learn more about biology.

Takeaway

  • Classification evolves with new genetic and cellular data; binomial nomenclature provides stable, universal names for species.