Introduction to Systematics

Introduction to Systematics

• Systematics is the branch of biology studying organism types, relationships, and evolutionary history
• Two main goals are:
  • Classifying and naming plant species globally
  • Reflecting evolutionary relationships and common ancestry in plant groupings
• Modern systematics is driven by molecular biology discoveries, especially DNA sequencing
• Phylogenetic trees visually represent evolutionary divergence
  • Oldest ancestors near the base, youngest descendants near the top

Binomial System of Nomenclature

• A standardized naming system for organisms
• Each organism has a unique two-part Latin name (genus + species)
• The genus name is capitalized, while the species name is not
• The name is italicized in print

Taxonomic Hierarchy

• The Linnaean hierarchical system groups organisms by increasing inclusiveness
• Species are grouped into genera, genera into families, families into orders, and so forth, up to kingdoms
• 'Taxon' is a general name given to the members of any level in the hierarchy

Evolutionary History

• Linnaeus' ideas transformed biological classification in the 18th century
• Darwin's theory of evolution revolutionized biology in the 19th century
• Molecular sequencing significantly changed phylogenetic understanding in the 20th century

Defining and Classifying Organisms

• Biologists use specific organism features for classification:
  • Presence/absence of a nucleus
  • Unicellular/multicellular structure and organelles
  • Mode of nutrition
  • Presence/absence of cell walls
  • Cell wall composition
  • Motility
  • Reproduction methods
  • Life cycle patterns

The Cell Nucleus

• The nucleus is an organelle containing the majority of genetic material (DNA)
• A nuclear membrane surrounds the nucleus

Cellular Organization

• Some organisms are unicellular, while others are multicellular
• Some unicellular organisms form filaments, sheets, or colonies

Nutrition Strategies

• Autotrophs produce their own food (photoautotrophs use sunlight, chemoautotrophs use chemicals)
• Heterotrophs obtain nutrients from other organisms (herbivores, carnivores, omnivores, saprophages)

Cell Walls

• Most organisms, except animals and some protists, have cell walls
• Bacteria have peptidoglycan cell walls
• Fungi have chitin cell walls
• Plant cells have cellulose cell walls

Motility

• Many organisms are motile (able to move)
• Various movement methods include flagella, cilia, or pseudopodia
• Some are sessile (attached)

Reproduction

• Reproduction can be asexual (no gametes) or sexual (fusion of gametes)
• Common asexual methods include fission, budding, and spore formation
• Sexual reproduction often involves alternation of generations

Life Cycles

• Three basic types of life cycles exist:
  • Zygotic meiosis (haploid organisms, diploid zygotes)
  • Gametic meiosis (diploid organisms, haploid gametes)
  • Sporic meiosis (alternation of generations)

Domains of Life

• Currently, three domains of life are recognized:
  • Archaea (also called Archaebacteria), Bacteria (also called Eubacteria), and Eukarya (or eukaryotes)
• Archaea and bacteria are prokaryotic (no nucleus or membrane-bound organelles)
  • DNA is circular

Viruses

• Viruses are characterized by a nucleic acid core (DNA or RNA) surrounded by protein
• Viruses require living cells to replicate
• Classification:
• Size, nucleic acid, and metabolic capabilities are important
• Symmetry (helical or icosahedral (20-sided)) is significant
• Some have envelopes, derived from host cell membranes
• Viruses are non-cellular
• Conical and rod-shaped capsids: some viruses have these shapes