Lesson #5 - Classification of Eukaryotic vs Prokaryotic

Linnaeus' Classification System

  • Linnaeus recognized only two kingdoms: animals and plants.

  • Micro-organisms also require classification.

  • Microscopes led to a better understanding of cellular structures.

Classification of Living Things

  • Biologists discovered prokaryotes and eukaryotes.

  • Classification includes domain, kingdom, cell type, and cell structures.

  • Domains: (chart attached on back)

    • Bacteria: Kingdom Eubacteria, prokaryote, cell walls with peptidoglycan, unicellular, autotroph or heterotroph (e.g., Streptococcus, Escherichia coli).

    • Archaea: Kingdom Archaebacteria, prokaryote, cell walls without peptidoglycan, unicellular, autotroph or heterotroph (e.g., Methanogens, halophiles).

    • Eukarya:

      • Protista: Eukaryote, cell walls of cellulose in some (chloroplasts in some), mostly unicellular (some colonial, some multicellular), autotroph or heterotroph (e.g., Amoeba, Paramecium, slime molds, giant kelp).

      • Fungi: Eukaryote, cell walls of chitin, most multicellular (some unicellular), heterotroph (e.g., Mushrooms, yeasts).

      • Plantae: Eukaryote, cell walls of cellulose; chloroplasts, multicellular, autotroph (e.g., Mosses, ferns, flowering plants).

      • Animalia: Eukaryote, no cell walls or chloroplasts, multicellular, heterotroph (e.g., Sponges, insects, fishes, mammals).

Phylogenetic Tree (chart attched on back)

  • A simple phylogenetic tree illustrates evolutionary relationships among the six kingdoms.

  • Archaea includes thermophiles, halophiles, and methanogens.

  • Eubacteria includes photosynthetic bacteria and purple bacteria.

  • Eukaryotes include animals, fungi, protists, and plants.

  • Diagram shows a divergence of ancestral eukaryotic cell to other kingdoms, including nonphotosynthetic eukaryotes, amoebozoa, brown algae, red algae, green algae.

Domains of Life (chart on back)

  • Domain is the highest taxonomic level; there are three domains of life: Eubacteria, Archaea, and Eukaryotes.

  • The diagram shows the most recent common ancestor of all living organisms.

  • Eubacteria: gram positives, purple bacteria, cyanobacteria, flavobacteria, thermotogales, green nonsulfur bacteria.

  • Archaea: methanosarcina, methanobacterium, methanococcus, thermoproteus, pyrodictium, haloarchaea

  • Eukaryotes: slime moulds, entamoebae, fungi, plants, ciliates, flagellates, trichomonads, diplomonads, microsporidia

Domain Composition

  • Domain Eubacteria contains only the Kingdom Eubacteria.

  • Domain Archaea contains only the Kingdom Archaea.

  • Domain Eukaryotes contains four Kingdoms: Protist, Animals, Plants, and Fungi.

Identifying, Naming & Classifying Species

  • Species is the most specific taxon.

  • Organisms in the same species share specific characteristics.

  • Scientists use multiple definitions to classify organisms because there is no single definitive definition of a species.

Species Concepts

  • Morphological Species Concept

    • Focuses on morphology (form & structure/function) of organism bodies (e.g., shape, size).

    • Compares to other similar organisms.

    • Considers change and variation of morphology.

  • Biological Species Concept

    • Focuses on the ability of two organisms to breed AND produce viable/fertile offspring.

  • Anatomical Evidence

    • Anatomical (Morphology) evidence helps determine how closely linked species are.

    • Homologous bone structures (e.g., forelimbs) indicate similar evolutionary history, even if limbs serve different purposes.

  • Physiological Evidence (phenotype)

    • Physiology focuses on organism biochemistry, including protein and enzyme structure & function.

    • Example: Guinea pigs were initially placed under Rodentia but moved to their own taxon after insulin protein studies.

  • Phylogenetic Species Concept

    • Focuses on evolutionary relationships, including specific DNA sequences.

    • Used to categorize past organisms and classify or reclassify species.

    • More shared evidence indicates closer relationships. (e.g. red pandas are more closely related to raccoons than giant pandas)

Human and Chimpanzee DNA

  • Chimpanzees are humans’ closest living relatives; humans and chimps share 98.8%98.8\% of their DNA.

  • Although chimpanzees & humans have many identical genes, they often use them in different ways. Certain genes are being expressed.

Prokaryotes: Eubacteria & Archaea

  • Single-celled organisms.

  • Lack membrane-bound organelles.

  • No nucleus; DNA in the nucleoid region.

  • Smallest organisms on Earth.

  • Dominant life forms in every habitat.

  • Vastly outnumber all living things.

  • Only about 10,000 prokaryote species have been isolated & identified.

  • Hard to identify all prokaryotes because many live in remote locations & extreme conditions

Importance of Prokaryotes

  • Bacteria are prokaryotic organisms (Eubacteria) most familiar to us.

  • Bacteria are responsible for many diseases (infectious bacteria are called pathogens).

  • Pathogens are disease-causing agents, often a viruses or microorganisms, that can lead to human deaths.

  • Bacterial diseases: strep throat, salmonella, tuberculosis, etc.

  • Infect livestock & crops, threatening food sources.

  • Bacteria & Archaea play key roles in recycling nutrients and biogeochemical cycles (e.g., nitrogen-fixing bacteria).

  • Photosynthetic bacteria are major producers of atmospheric oxygen.

  • Mutualism: a relationship where both species benefit.

    • Humans rely on bacteria in the large intestine to produce vitamins K & B12.

  • Bacteria produce antibiotics (substances that kill or weaken microorganisms).

    • Natural antibiotics are produced by bacteria & fungi; synthetic antibiotics are manufactured.

Eukaryotes

  • Multicellular (most) cell.

  • Membrane-bounded organelles.

  • Nucleus for DNA storage.

  • Internal membranes likely developed from the folded cell membrane of an ancestral prokaryotic cell, increasing surface area for material exchange.

  • Mitochondria & Chloroplast used to be a prokaryotic cell but was engulfed by another cell.

  • Their inner membranes are similar to their ancestral prokaryote, while their outer membranes match the cell membrane of eukaryotes.

  • Mitochondria & chloroplast have their own chromosomes (DNA).

  • Originated by endosymbiosis: a single-celled organism lives within the cell(s) of another organism.

  • Mitochondria were once aerobic prokaryotes, related to modern proteobacteria.

    • Inside eukaryotic cells, benefited from a rich food supply, while eukaryotes benefited from excess energy from the aerobic prokaryote.

  • Chloroplast were likely once photosynthetic prokaryotes.

    • Inside early eukaryotes, benefited from carbon dioxide waste produced by eukaryotes, which they used in photosynthesis.

    • Eukaryotes benefited from excess oxygen made by the prokaryotes. (photosynthesis)