Diversity of Life and Taxonomy

Binomial Nomenclature and Scientific Names

Binomial nomenclature is the formal system for naming species, established by Carolus Linnaeus. Each species receives a two-part scientific name: the genus and the species epithet.

• Genus: Capitalized and italicized (e.g., Homo).

• Species: Lowercase and italicized (e.g., sapiens).

• Correct format: Homo sapiens

• Incorrect formats: Homo sapiens (not italicized), Homo Sapiens (species capitalized), homo sapiens (genus not capitalized), Homo (genus only).

Taxonomy is the branch of biology that identifies, names, and categorizes living organisms.

Taxonomic Hierarchy: Inclusive vs. Exclusive

Taxonomic levels organize life from broadest to most specific. Higher levels are more inclusive; lower levels are more exclusive.

• Domain (most inclusive)

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species (most exclusive)

Mnemonic: "King Philip Came Over For Good Soup" (Domain can be added at the top).

The Three Domains of Life

Modern classification recognizes three domains:

• Bacteria: Prokaryotic, single-celled, no nucleus.

• Archaea: Prokaryotic, single-celled, often extremophiles; more closely related to Eukarya than to Bacteria.

• Eukarya: Eukaryotic cells with a nucleus; includes protists, plants, fungi, and animals.

Key Point: Archaea and Bacteria are both prokaryotes, but Archaea are evolutionarily closer to Eukarya.

Whittaker's Five Kingdoms (1969)

Originally, organisms were classified into two kingdoms (plants and animals). Whittaker expanded this to five, based on cell type and nutrition:

Additional info: Modern classification uses domains and supergroups because protists are not monophyletic.

Key Groups: Prokaryotes, Protists, Protostomes, Deuterostomes, Eumetazoans, Parazoans

• Prokaryotes: Bacteria and Archaea; no nucleus.

• Protists: Unicellular eukaryotes; not a monophyletic group.

• Protostomes: Mouth develops first; spiral, determinate cleavage. Examples: Mollusca, Annelida, Arthropoda.

• Deuterostomes: Anus develops first; radial, indeterminate cleavage. Examples: Echinodermata, Chordata.

• Eumetazoans: True animals with tissues and symmetry.

• Parazoans: Sponges; no true tissues, no symmetry.

Phylogenetic Groups and Evolutionary Relationships

Monophyletic, Paraphyletic, Polyphyletic Groups

Phylogenetic trees illustrate evolutionary relationships. Groups are defined by their ancestry:

How to identify: Trace back to the most recent common ancestor. If all descendants are included, it's monophyletic; if some are missing, paraphyletic; if the trait evolved independently, polyphyletic.

Key Terms: Phylogeny, Cladistics, Parsimony, Synapomorphy, Homoplasy

• Phylogeny: Evolutionary history and relatedness among organisms.

• Cladistics: Method for building trees using shared, derived traits (synapomorphies).

• Parsimony: Principle that the simplest explanation (fewest evolutionary changes) is preferred.

• Synapomorphy: Shared, derived trait defining a monophyletic group (e.g., milk in mammals).

• Homoplasy: Similar trait not inherited from a common ancestor; results from convergent evolution (e.g., social behavior in humans and dolphins).

Homology vs. Homoplasy: Homology is similarity due to shared ancestry; homoplasy is similarity due to independent evolution.

Evolutionary Innovations in Plants

Key Plant Innovations and Their Functions

Plants evolved several innovations to adapt to terrestrial life:

Capillary action: Water moves up xylem tubes via cohesion and adhesion.

Seed vs. Fruit: Ovule becomes the seed; ovary becomes the fruit. Seeds are for reproduction; fruits are for dispersal.

Gymnosperms vs. Angiosperms

Gymnosperms: Cone-bearing, wind-pollinated, lack flowers and fruits.

Angiosperms: Flowering plants, efficient pollination, fruits for dispersal.

Synapomorphy: Seed defines seed plants; flower defines angiosperms.

Evolutionary Innovations in Animals

Key Animal Innovations

Animal evolution is marked by innovations related to motility and complexity:

• Tissues: Groups of similar cells; sponges lack true tissues, all other animals have them.

• Symmetry: None (sponges), radial (cnidarians), bilateral (most animals).

• Cephalization: Concentration of nervous system and sense organs at the head; associated with bilateral symmetry.

• Segmentation: Repetition of body parts (annelids, arthropods).

Directional terms: Anterior (front), posterior (rear), dorsal (back), ventral (belly).

Major Animal Groups and Their Features

Additional info: Corals and sea anemones are cnidarians. Chordates are defined by the notochord.

Chordate Groups: Inclusive vs. Exclusive

Chordate classification is hierarchical, from most to least inclusive:

• Eukarya: All organisms with a nucleus.

• Eumetazoa: All animals except sponges.

• Deuterostoma: Echinoderms and chordates.

• Chordata: Animals with a notochord.

• Vertebrata: Chordates with a backbone.

• Gnathostoma: Vertebrates with jaws.

Exceptions: Hagfish are craniates but not vertebrates; lampreys are vertebrates but jawless.

Gnathostome Classes

• Chondrichthyes: Cartilaginous fishes (sharks, rays).

• Osteichthyes: Bony fishes (ray-finned, lobe-finned).

• Amphibia: Ectothermic, shell-less eggs, must reproduce in water.

• Reptilia: Amniotic tetrapods with bony skeleton.

• Aves: Birds; endothermic, feathers, toothless beak.

• Mammalia: Endothermic, mammary glands, fur/hair.

Key innovation sequence: Notochord → Cranium → Vertebral column → Jaws → Four limbs → Amniotic egg → Milk/feathers.

Tetrapods: Vertebrates with four limbs.

Amniotic egg: Shelled, fluid-filled egg; allows reproduction away from water.

Oviparous: Egg-laying; Viviparous: Live birth.

Primates: Bipedalism is a key trait.

Practice Questions and Exam Tips

• Scientific name: Genus capitalized, species lowercase, both italicized.

• Hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

• Three domains: Bacteria, Archaea, Eukarya; Archaea closer to Eukarya.

• Whittaker's five kingdoms: Use cell count, cell type, and nutrition.

• Monophyletic: Ancestor plus all descendants; Paraphyletic: Ancestor plus some; Polyphyletic: No shared ancestor with trait.

• Synapomorphy vs. Homoplasy: Synapomorphy defines monophyletic groups; homoplasy results from convergent evolution.

• Plants: Cuticle, stomata, xylem, lignin, seed, flower, fruit. Gymnosperms lack flowers and fruit; angiosperms have all.

• Animals: Parazoa (sponges), Eumetazoa (true animals), radiates (cnidarians), bilaterians (protostomes, deuterostomes).

• Nesting order: Eukarya → Eumetazoa → Deuterostoma → Chordata → Vertebrata → Gnathostoma.

• Exceptions: Hagfish (craniate, not vertebrate); lampreys (vertebrate, no jaw).