The main idea
Don't overthink this unit. It is merely: a) a description of how prokaryotes work, and b) a description of how they fit into the tree of life.
Describe the conditions of life on the early Earth and the four stages that might have produced the first cells on Earth.
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Physical conditions on the early earth differed significantly from today, especially in the lack of atmospheric oxygen -
Life may have evolved from inorganic matter via four main stages:
- Abiotic synthesis of small organic molecules
- Polymerization of these small molecules into macromolecules
- Packaging of these molecules into "protobionts"
- The origin of self-replicating molecules that could undergo natural selection and eventually make inheritance possible
Several steps important to life have been demonstrated to self-organize in the laboratory -
RNA might have served as the earliest genetic material and enzymes (ribozymes)
Describe the diverse roles, abundance, shapes and structures of prokaryotic life
Prokaryotes (=Monera) represent the simplest life forms, and fossils indicate they were the earliest living things.
- They lack membrane-bound organelles, and elements of their ribosomes function differently
- They have structures that are either unique or are constructed in a unique way (pili, endospores, capsules, cell walls)
- They can be characterized by their shapes (coccus, bacillus or spirillum), reactions to dyes (e.g. Gram stain) and colony shape and color or molecular tools.
- They obtain nutrition a variety of ways: (chemo- and, photo-autotrophic and, heterotrophic)
- Two domains (see below for more detail): Bacteria and Archaea
Compare the characteristics of the three domains of life and explain why Archaea are considered to be more closely related to Eukarya than to Bacteria
Two domains of prokaryotes:
- Archaea are simpler, but show molecular homologies with eukaryotes; mostly extreme environments (thermophiles, halophiles)
- Bacteria are important in food chains, fixing nitrogen and processing nutrients, as disease organisms (and potential biological weapons), or environmental remediation
- Know differences between Bacteria and Archaea (16.8)!
Eukaryotes
- The eukaryotic cell has membrance-bound organelles and probably originated as a community of prokaryotes (mitochondria and chloroplasts from symbiotes)
- The simplist groups of eukayotes are termed "Protists", but this is probably a polyphyletic group
- Three main divisions based on feeding and size: Protozoa (single-celled heterotrophs), Algae (single-celled autotrophs) and Seaweeds (multi-celled autotrophs)
Explain the endosymbiotic theory of eukaryote origins and how multicellular life likely evolved from colonial protists
- Review endosymbiotic theory (section 4.16) and distinguish between primary and secondary endosymbiosis (Fig. 16.12)
- True multicellularity requires specialization of cells, interdependence and coordination
- Multicellular life evolved from colonial protists several times independently
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