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Tree of Life. Planet Earth is about 4.6 billion years old. Oldest known rocks are about 3.8 billion years old. Oldest fossils (prokaryotes) are about 3.5 billion years old. Tree of Life. All living organisms on this planet share a common ancestor.

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tree of life
Tree of Life
  • Planet Earth is about 4.6 billion years old.
  • Oldest known rocks are about 3.8 billion years old.
  • Oldest fossils (prokaryotes) are about 3.5 billion years old.
tree of life2
Tree of Life
  • All living organisms on this planet share a common ancestor.
  • The tree of life reflects the branching pattern of speciation (phylogenetic history of life) that has occurred since the origin of life.
tree of life3
Tree of Life
  • There is an excellent Tree of Life website in which you can trace the branching pattern of the history of life and explore classification.
tree of life4
Tree of Life
  • There is a hierarchichal classification of life in which organisms are progressively nested within larger and larger categories as more distant relatives are included in the classification (we will explore classification shortly).
  • The highest level of classification is the Domain of which there are three.
domains bacteria and archaea
Domains Bacteria and Archaea
  • Domain Bacteria
  • Domain Archaea
  • The domains Bacteria and Archaea are both prokaryotes (they have no nucleus and the DNA is not arranged in chromosomes). Prokaryote derived from the Greek Pro meaning before and karyon meaning a kernel [i.e. a nucleus]
domain bacteria
Domain Bacteria
  • Includes most of the bacteria people are familiar with including disease-causing species (Salmonella; Vibriocholerae which causes cholera), nitrogen-fixing (Nitrosomonas) and parasites (Borreliaburgdorferi which causes Lyme disease).
domain bacteria11
Domain Bacteria
  • Bacteria play a major role in decomposition and many live symbiotically with other organisms including humans helping to break down or synthesize foods needed by the host.
domain archaea
Domain Archaea
  • The Archaea include many extremophiles, organisms that live in extreme environments.
  • Includes thermophiles which tolerate extreme heat (e.g. live in geysers and hot springs where temps may reach 90 degrees celsius) and halophiles (salt lovers, which live in very saline environments (e.g. Great Salt Lake, Dead Sea)
bacteria and archaea
Bacteria and Archaea
  • Bacteria and Archaea are both prokaryotes and their DNA is arranged in circular structures called plasmids.
  • However, they have substantial differences in their biochemistry, cell wall structure and other molecular details.
bacteria vs archaea
Bacteria vs. Archaea
  • Bacteria are inhibited by antibiotics Streptomycin and Chloramphenicol but Archaea are not.
  • Archaea in common with Eukarya have histone proteins associated with their DNA, have introns in their DNA, and have several kinds of RNA polymerase. Bacteria lack these features.
  • Archaea and Eukarya thus are members of a clade.
domain eukarya
Domain Eukarya
  • Domain Eukarya contains the eukaryotic organisms (from Greek eu true and karyon akernal) which have a true nucleus and DNA arranged in chromosomes.
  • Eukaryotic cells are much larger and complex than prokaryotic cells and contain organelles such as mitochondria, chloroplasts, and lysosomes.
domain eukarya17
Domain Eukarya
  • Domain Eukarya includes three kingdoms the Plantae, Fungi and Animalia.
  • There are also a number of unicellular eukaryotes that may form as many as five other kingdoms. These were formerly grouped in the paraphyletic group the Protista.
domain eukarya18
Domain Eukarya
  • Plantae, Fungi and Animalia are mostly multicellular, but plants are autotrophic (produce their own food by photosynthesis) whereas the fungi and animals are heterotrophic (consume other organisms).
  • Unlike animals, plants remain in one place and produce food through photosynthesis. They trap the energy in sunlight and store it in chemical bonds.
  • The energy stored in chemical bonds can then be used to fuel metabolic processes.
  • To carry out photosynthesis plants must obtain water and minerals from the soil, CO2 from the air, and light from the sun.
  • The structure of plants reflects their need to carry out these tasks.
basic structure of plants
Basic structure of plants
  • Plants have three basic organs:
    • Roots
    • Stems
    • Leaves
  • These organs are organized into two systems: the largely below-ground root system and the above-ground shoot system (stems and leaves).
  • Fungi are heterotrophs and feed by absorption.
  • They secrete enzymes outside their bodies (exoenzymes) which break down complex molecules to simpler ones which the fungus can absorb.
  • Some fungi are unicellular (yeasts), but most are multicellular.
  • Body of multicellular fungi made up of tiny filaments called hyphae.
  • The hyphae form a mass called a mycelium that penetrates the medium the fungus is feeding on.
  • Mushrooms and toadstools are the familiar reproductive structures of fungi.
  • Fungi produce spores which may be sexually or asexually produced
  • Fungi and Animalia share a more recent common ancestor (about 1.5 billion years ago) than they do with Plantae.
  • Fungi are believed to have evolved from flagellated single-celled protistans, which suggests multicellularity arose independently in Fungi and Animalia
  • Since zoology is the study of animals, the kingdom Animalia is the focus of this semester although we will briefly discuss the single-celled protozaon groups.
  • Animals are heterotrophic eukaryotes. Most are multicellular.
  • Except for sponges all animals have tissues which are specialized collections of cells separated from other tissues by membranes.
  • Tissues are arranged together to produce organs and organs are organized into organ systems (e.g. digestive system).
  • Most animals are bilaterally symmetrical and form a large clade called the Bilateria.
  • Bilateral animals have a left and right side, top and bottom, as well as front and rear ends.
  • A smaller number are radially symmetrical (e.g. jellyfish).