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The Origin and Evolution of Microbial Life: Prokaryotes and Protists PROKARYOTES 16.7 Prokaryotes have inhabited Earth for billions of years Prokaryotes are the oldest life-forms And remain the most numerous and widespread organisms Figure 16.7 Colorized SEM 650 Three Domains – Archaea, Bacteria, Eukarya 16.8 Bacteria and archaea are the two main branches of prokaryotic evolution Domains Bacteria and Archaea Are distinguished on the basis of nucleotide sequences and other molecular and cellular features Differences between Bacteria and Archaea Table 16.8 16.9 Prokaryotes come in a variety of shapes Prokaryotes may be shaped as Colorized SEM 12,000 Figure 16.9A–C Colorized SEM 3,000 Spheres (cocci) Rods (bacilli) Curves or spirals (vibrio or spirochaete) Colorized SEM 9,000 16.10 Various features contribute to the success of prokaryotes I. External Structures i. Cell wall ii. Pili iii. Flagella II. Reproduction and adaptation III. Specialized internal structures IV. Form colonies V. Varied methods of obtaining food External Structures The cell wall Is one of the most important features of nearly all prokaryotes Is covered by a sticky capsule Capsule Figure 16.10A Colorized TEM 70,000 Some prokaryotes Stick to their substrate with pili Colorized TEM 16,000 Pili Figure 16.10B Flagellum Colorized TEM 14,000 Motility Many bacteria and archaea Are equipped with flagella, which enable them to move Plasma membrane Cell wall Figure 16.10C Rotary movement of each flagellum Reproduction and Adaptation Prokaryotes Have the potential to reproduce quickly in favorable environments Some prokaryotes can withstand harsh conditions By forming endospores TEM 34,000 Endospore Figure 16.10D Internal Organization Some prokaryotic cells Have specialized membranes that perform metabolic functions Figure 16.10E Thylakoid membrane TEM 6,000 TEM 45,000 Respiratory membrane 16.11 Prokaryotes obtain nourishment in a variety of ways As a group Prokaryotes exhibit much more nutritional diversity than eukaryotes Types of Nutrition Autotrophs make their own organic compounds from inorganic sources Photoautotrophs harness sunlight for energy and use CO2 for carbon Chemoautotrophs obtain energy from inorganic chemicals instead of sunlight Heterotrophs obtain their carbon atoms from organic compounds Photoheterotrophs can obtain energy from sunlight Chemoheterotrophs are so diverse that almost any organic molecule can serve as food for some species Figure 16.11A Nutritional classification of organisms Table 16.11 Metabolic Cooperation In some prokaryotes Metabolic cooperation occurs in surfacecoating colonies called biofilms Figure 16.11B Colorized SEM 13,000 16.12 Archaea thrive in extreme environments (extremophiles) — and in other habitats Archaea are common in Salt lakes, acidic hot springs, deep-sea hydrothermal vents Figure 16.12A, B Archaea are also a major life-form in the ocean Plankton dispersal Phytoplankton 16.13 Bacteria include a diverse assemblage of prokaryotes Bacteria are currently organized into several subgroups, LM 13,000 Figure 16.13A, B Colorized TEM 5,000 including Proteobacteria Chlamydias Spirochetes Figure 16.13C, D Nitrogen-fixing cells Photosynthetic cells LM 650 Colorized SEM 2,8000 Gram-positive bacteria Cyanobacteria, which photosynthesize in a plantlike way Colorized SEM 2,800 CONNECTION 16.14 Some bacteria cause disease Pathogenic bacteria cause disease by producing Exotoxins or endotoxins SEM 12,000 Spirochete that causes Lyme disease Figure 16.14A, B “Bull’s-eye”rash SEM 2,800 Tick that carries the Lyme disease bacterium CONNECTION 16.15 Bacteria can be used as biological weapons Bacteria, such as the species that causes anthrax Can be used as biological weapons Figure 16.15 CONNECTION 16.16 Prokaryotes help recycle chemicals and clean up the environment Bioremediation Is the use of organisms to clean up pollution Prokaryotes are decomposers in Sewage treatment and can clean up oil spills and toxic mine wastes Rotating spray arm Rock bed coated with aerobic bacteria and fungi Liquid wastes Figure 16.16A, B Outflow PROTISTS 16.17 The eukaryotic cell probably originated as a community of prokaryotes Eukaryotic cells Evolved from prokaryotic cells more than 2 billion years ago The nucleus and endomembrane system Probably evolved from infoldings of the plasma membrane Mitochondria and chloroplasts Probably evolved from aerobic and photosynthetic endosymbionts, respectively Endosymbiotic Theory Cytoplasm Plasma membrane Ancestral prokaryote A model of the origin of eukaryotes Endoplasmic Nuclear reticulum Nucleus envelope Membrane infolding Aerobic heterotrophic prokaryote Cell with nucleus and endomembrane system Some cells Ancestral host cell Photosynthetic prokaryote Endosymbiosis Mitochondrion Chloroplast Mitochondrion Figure 16.17 Photosynthetic eukaryotic cell 16.18 Protists are an extremely diverse Figure 16.18 LM 275 assortment of eukaryotes Protists Are mostly unicellular eukaryotes Molecular systematics Is exploring eukaryotic phylogeny Alveolates Stramenopila Figure 16.19 Ancestral eukaryote Green algae Red algae Animals Choanoflagellates Fungi Plants Closest algal relatives of plants Amoebozoa Cellular slime molds Plasmodial slime molds Amoebas Brown algae Diatoms Water molds Ciliates Apicomplexans Dinoflagellates Euglenozoans Diplomonads How are Protists classified? 16.19 A tentative phylogeny of eukaryotes includes multiple clades of protists The taxonomy of protists Is a work in progress 16.20 Diplomonads and euglenozoans include some flagellated parasites The parasitic Giardia Is a diplomonad with highly reduced mitochondria Figure 16.20A Colorized SEM 4,000 Euglenozoans Figure 16.20B, C Colorized SEM 1,300 Include trypanosomes and Euglena Colorized SEM 1,300 16.21 Alveolates have sacs beneath the plasma SEM 2,300 membrane and include dinoflagellates, apicomplexans, and ciliates Dinoflagellates Are unicellular algae Figure 16.21A Apicomplexans are parasites Such as Plasmodium, which causes malaria Apex Figure 16.21B Red blood cell TEM 26,000 Cilliates Use cilia to move and feed Cilia LM 60 Macronucleus Figure 16.21C 16.22 Stramenopiles are named for their “hairy” flagella and include the water molds, diatoms, and brown algae This clade includes Fungus-like water molds Figure 16.22A Photosynthetic, unicellular diatoms Figure 16.22B LM 400 Brown algae, large complex seaweeds Figure 16.22C 16.23 Amoebozoans have pseudopodia and include amoebas and slime molds Amoebas Figure 16.23A Move and feed by means of pseudopodia LM 185 A plasmodial slime mold is a multinucleate plasmodium That forms reproductive structures under adverse conditions Figure 16.23B Cellular slime molds Have unicellular and multicellular stages 45 Figure 16.23C Reproductive structure 15 Amoeboid cells LM 1,000 Slug-like aggregate 16.24 Red algae and green algae are the closest relatives of land plants Red algae Contribute to coral reefs Figure 16.24A Green algae May be unicellular, colonial, or multicellular Chlamydomonas LM 80 LM 1,200 Volvox colonies Figure 16.24B The life cycles of many algae Involve the alternation of haploid gametophyte and diploid sporophyte generations Mitosis Male gametophyte Spores Gametes Mitosis Meiosis Female gametophyte Fusion of gametes Sporophyte Zygote Mitosis Figure 16.24C Key Haploid (n) Diploid (2n) 16.25 Multicellularity evolved several times in eukaryotes Multicellularity evolved in several different lineages Probably by specialization of the cells of colonial protists Gamete 2 1 Unicellular protist Figure 16.25 Colony Locomotor cells 3 Foodsynthesizing cells Early multicellular organism with specialized, interdependent cells Somatic cells Later organism that produces gametes Multicellular life arose over a billion years ago