Unformatted text preview: Ch 26-28 review Geologic history & biological history have been episodic, marked by revolutions that opened many new ways of life CHANCE likely played a big role in evolution Earth formed about 4.6 bya, along w/ the rest of the solar system Earth's early atmosphere contained water vapor & chem's released by volcanos *oxygen was not present in earth's early atmosphere, or if it was it was in VERY minute quantities WAYS LIFE MAY HAVE BEGAN ON EARTH Instead of forming in the atmos, the 1st organic compounds may have been synthesized near submerged volcanoes & deep-sea vents organic compounds from which the 1st life on Earth arose may have come from space C compounds have been found in some meteorites that landed on Earth The possibility that life is not restricted to Earth is becoming more accessible to scientific testing Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock Chem & physical processes on early Earth may have made simple cells via a seq of stages: 1. Abiotic synthesis of small organic molecules 2. Joining the small molecules into polymers 3. Packaging of molecules into "protobionts" 4. Origin of self-replicating molecules * An RNA polymer was likely the 1st The change to DNA based genetic systems was likely b/c: DNA is chemically more stable & replicates w/ fewer errors (mutations) than RNA All of the following have been synthesized in lab experiments, by scientists studying the origin of life: liposomes liposomes w/ selectively permeable membranes oligopeptides & other oligomers amino acids fossil record chronicles a # of occasions when global environmental changes were so rapid & disruptive that a majority of spp were swept away geologic record has 3 eons: Archaean, Proterozoic, & Phanerozoic Phanerozoic eon has 3 eras: the Paleozoic, Mesozoic, & Cenozoic Stromatolites date back 3.5 bya & r oldest known fossils & resemble bacterial communities found today in some warm, shallow, salty bays Prok's were Earth's sole inhabitants from 3.5 to about 2 bya earliest types of photosynthesis did not produce O2 Oxygenic photosynthesis probably evolved about 3.5 billion years ago in cyanobacteria oldest fossils of euk cells date back 2.1 bya Theory of endosymbiosis mitochondria & plastids were formerly small prok's living w/in larger host cells Modern mitochondria are the descendants of what were once free-living alpha proteobacteria As mitochondria become inactive during periods of O2 debt, what is probably true of their alpha proteobacterial ancestors is that they were obligate aerobes & heterotrophs prok ancestors of mitochondria & plastids probably gained entry to the host cell as engulfed, originally freeliving prokaryotes becoming more interdependent, the host & endosymbionts would have become a single organism Key evidence supporting an endosymbiotic origin of mitochondria & plastids: Similarities in inner membrane structures & functions Both replicate by binary fission (like prok's) Both w/ own circular DNA w/o histones Ribosomes are similar to bacteria Same size as bacteria The oldest known fossils of euk's are of relatively small algae that lived about 1.2 billion years ago Multicell euk's didn't evolve until after "snowball earth" ~500-750mya (life only in water until the earth thawed!) The Cambrian explosion is assoc'd in time w/ the end of the period known as snowball Earth formation of supercontinent Pangaea during the late Paleozoic era (250mya) & its breakup during the Mesozoic era (180mya) explains many biogeographic puzzles Ocean basins became deeper, this lowered the sea level & drained shallow coastal seas Most marine species lived in shallow waters so the formation of Pangaea killed off most of them A major evolutionary episode that corresponded in time most closely w/ the formation of Pangaea was the Permian extinctions Most of the major phyla of animals appear in the fossil record of the first 20 my's of the Cambrian period 2 animal phyla, Cnidaria & Porifera, are older, dating from the late Proterozoic Plants, fungi, & animals colonized land about 500 mya Symbiotic relationships b/w plants & fungi are common today & date from this time CH 27 Prok's Prok's thrive everywhere; even in too acidic, too salty, too cold, or too hot for most other organisms Most prok's are unicellular, but some spp form colonies 3 shapes: spheres (cocci), rods (bacilli), & spirals most prok cells have a cell wall (most w/ peptidoglycan); maintains cell shape, protection, & prevents cell bursting in a hypotonic environ Using Gram stain, scientists classify many bacterial spp into groups based on cell wall composition; Gram-positive has peptidoglycan & Gram-negative less peptidoglycan & often has an outer membrane w/ toxic lipopolysaccharides cell wall of many prok's is covered by a capsule, a sticky layer of polysaccharide or protein Plants, fungi & bacteria all have cell walls, but we classify them diff taxonomically b/c their cell walls are made of very diff biochemicals
Some prok's have fimbriae & pili, that let them to stick to their substrate or other indiv's in a colony prok genome is a ring of DNA that is not surrounded by a membrane & in a nucleoid region Endospores-Not in all bacteria, this structure enables it to germinate after exposure to harsh conditions, such as boiling Sex pilus- structure that permits conjugation to occur Flagellum-req's ATP to function, & permits some spp to respond to taxes Cell wall-an impt source of endotoxin in gram-negative species; composed almost entirely of peptidoglycan Capsule-Not in all bacteria, this slimy material enables cells that possess it to resist the defenses of host organisms Prok's can metabolize N in a variety of ways In N fixation, some prok's convert atmospheric N to ammonia Archaea share certain traits w/ bacteria & other traits w/ euk's 3 types: methanogens (live in cow guts), thermophiles (hot springs), halophiles (salt lakes) Prok's are so impt to the biosphere that if they disappear, any other life would not survive they are very useful to us and other organisms Prok's play a major role in the continual recycling of chem elements b/w living & nonliving components of ecosystems Chemoheterotrophic prok's function as decomposers, breaking down corpses, dead vegetation, & waste products Bioremediation- Using prok's to remove pollutants from the environ (ex: prok's to treat sewage or clean up oil spills) Jams, jellies, preserves, honey, & other foodstuffs w/ high sugar content hardly ever become contaminated by bacteria, even when the food containers are left open at room tm b/c bacteria that encounter this type of environment undergo death by plasmolysis Ch 28 protists ALL are eukaryotic The evolution of euk's from prok's probably: occurred many times; involved endosymbiosis on multiple occasions; allowed for complexity & multicellularity. Diplomonads-- 2 nuclei & possess more 2 identical, functional flagella Parabasalids-- trichomonads; move by flagella & an undulating part of the pm Euglenozoa-- diverse clade w/ predatory heterotrophs, have 1 normal & 1 crystalline-rod-containing flagellum Alveolata membrane-bounded sacs (alveoli) just under the pm ---- dinoflagellates- 1 flagellum oriented at 90 degrees to the 2nd flagellum & an produce potent neurotoxins that cause extensive fish kills, contaminate shellfish, & create severe respiratory irritation to humans ----Apicomplexa- malaria (Plasmodium spp.) ----Ciliophora (ciliates)- paramecium have a process that results in genetic recombination, but is separate from the process wherein the pop size of paramecium 's called conjugation Stramenopila several groups of heterotrophs & certain groups of algae; 1 hairy & 1 smooth flagellum ----Oomycetes- water molds, white rusts, & downy mildews **irish potato famine ---- Diatoms unicellular algae w/ a unique 2part, glass-like wall of hydrated silica; major component of phytoplankton **Concerning diatoms' potential use as drugdelivery systems, the porous nature of their cell walls is the anatomical feature that is most impt for this application ----Golden algae, or chrysophytes- named for their color, which results from their yellow & brown carotenoids ---Brown algae, or phaeophytes- largest & most complex algae; many spp called seaweeds Cercozoa & Radiolarians; amoebas, Foraminiferans, & radiolarians Amoebozoans amoeba that have lobeshaped, rather than threadlike, pseudopodia Rhodophyta- Red algae, usu multicellular; lgst r seaweeds Chlorophyta (caulerpa, chlamydomonas) green algae; 2 identical, functional flagella, roughly parallel to each other & emerging from about the same site **watermelon snow **Members of the green algae often differ from members of the plant kingdom in that some green algae are unicellular Explain the endosymbiotic theory of the origin of eukaryotic cells Discuss 3 ex's of evidence supporting this theory Describe how bacteria protect themselves against environmental threats Give 2 ex's in your explanation The 5-kingdom system of classification has been replaced with a more accurate 3-domain system What were the 5-kingdoms of the old system? What are the 3 domains of life? What kingdom has become obsolete? What are the characteristics that define each of those domains? What evidence did scientists use to develop the 3-domain system? Provide 3 adaptations found in various prok's Explain how these 3 adaptations have ensured the success of prok's Discuss how prok's in earth's early history changed the environments on earth Discuss 2 ways in which prok's continue to have an ecological impact today ...
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- Spring '10
- Bacteria, prok, ecosystems Chemoheterotrophic prok, small prok, prok cells, prok genome