LJ

M1-Bio2-_CLASSIFICATION_OF_ORGANISMS (1)

Classification of Organisms

Taxonomy and Classification

  • Definition: Classification of living organisms based on shared characteristics.

  • Methods of classification include:

    • Comparison of appearance, anatomy, and structure.

    • Data from development, physical anatomy, biochemistry, DNA, behavior, ecological preferences, reproduction, mobility, and functionality.

  • Organisms are grouped hierarchically into smaller categories based on detailed similarities to aid scientific study.

Historical Perspectives in Classification

  • Early classifications:

    • Humans categorized into groups: Humans, Animals (e.g., cats & fishes), Plants (e.g., trees & grass), Non-living beings (e.g., rocks).

Evolution and Classification

  • Diversity of life on Earth is a result of evolution over billions of years (3.5 - 4.5 billion).

  • Evolution refers to changes in species over time, with fossils serving as evidence of past life and evolutionary processes.

Timeline of Evolution

  • Key events include:

    • Big Bang: approx. 14 billion years ago.

    • Formation of Earth: approx. 4.5 billion years ago.

    • First prokaryotic organisms and the development of eukaryotes: 1.5 billion years ago.

    • Cambrian explosion (~541 million years ago): emergence of diverse life forms (sponges, annelids, arthropods, etc.).

    • Evolution of key organisms: Fish, reptiles, birds, and mammals emerging over time.

Theories of Evolution

  • Several theories address how organisms evolved:

    • Special creation, spontaneous generation (abiogenesis), biogenesis, and chemical evolution.

  • Evidence for evolution includes:

    • Morphology and anatomy (homologous, analogous, and vestigial organs).

    • Lamarckism (use and disuse theory) and Darwinism (natural selection).

    • Paleontology (fossils).

The Six Kingdom Classification Scheme

  • Major kingdoms include:

    • Animalia (multicellular, eukaryotic).

    • Plantae (multicellular, eukaryotic).

    • Fungi (multicellular, eukaryotic).

    • Protista (unicellular and multicellular, eukaryotic).

    • Eubacteria (unicellular, prokaryotic).

    • Archaebacteria (unicellular, prokaryotic).

Characteristics of Major Kingdoms

  • Key characteristics include:

    • Mobility: Eukaryotic, some mobile, others sessile.

    • Nutrition: Heterotrophic vs. autotrophic (photosynthesis and/or chemosynthesis).

    • Cellular structure: Cell walls (cellulose in plants, chitin in fungi, peptidoglycan in bacteria).

Systematics and Taxonomy

  • Systematics: The science of organizing the diversity of life and studying evolutionary relationships.

    • Taxonomy: A branch focusing on identification, classification, and naming organisms.

    • Aristotle's early system classifying organisms by appearance, Linnaeus’s binomial nomenclature system proposed a two-name category for species.

Cladistics

  • Cladistics focuses on monophyletic groups (common ancestors and descendants).

  • Cladograms visually represent the phylogeny of organisms based on derived characteristics.

Linnaean Classification System

  • Hierarchical classification:

    • Domain, Kingdom, Phylum/Division, Class, Order, Family, Genus, Species.

    • Mnemonic for taxonomy: "Did King Philip Call Out For a Good Soup?"

  • Example taxonomy for humans:

    • Domain: Eukarya

    • Kingdom: Animalia

    • Phylum: Chordata

    • Class: Mammalia

    • Order: Primates

    • Family: Hominidae

    • Genus: Homo

    • Species: sapiens.

Classification Comparison

  • Summary of classifications across various systems (Linnaeus, Haeckel, Whittaker, Woese).

  • Cladistics compared with traditional classifications highlighting evolutionary relationships among organisms.

Types of Evidence for Classification

  • Fossil records (relative and radioactive dating) validate evolutionary lineage.

  • Comparative anatomy distinguishes homologous (similar structure) and analogous traits (similar function).

  • Comparative embryology examines developmental stages across species revealing common ancestry.

  • Biochemical information utilizes DNA and protein analysis for evolutionary relationships.

  • Heredity studies inheritance patterns helping classify organisms.

  • Cellular structure, behavior, and geographical range are critical in taxonomy.

Dichotomous Key

  • A tool for identifying organisms through binary choices based on characteristics.

  • Steps include dividing organisms into two groups based on a trait, leading to eventual identification of each specimen's name.

Constructing a Dichotomous Key

  • Process involves separating organisms/features logically until each has distinct characteristics.

  • Methods can include physical traits and observable behaviors.

Summary and Conclusion

  • Classification helps systematize and understand the relationships and traits of the diverse life forms.

  • Acknowledges the complexities and continuous adaptation of organisms over time.