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Introduction: How Ancient Bacteria Changed the World Virtually all metabolic pathways on Earth evolved in prokaryotic cells, before the evolution of eukaryotes The products generated by prokaryotic metabolism changed the Earth’s atmosphere and rocks Fossilized stromatolites from 3 billion years ago contain the fossils of photosynthetic cyanobacteria – These bacteria produced O2 and made Earth’s atmosphere aerobic Copyright © 2009 Pearson Education, Inc. Introduction: How Ancient Bacteria Changed the World Living stromatolites still form in the warm, shallow waters of Shark Bay, western Australia Copyright © 2009 Pearson Education, Inc. PROKARYOTES Copyright © 2009 Pearson Education, Inc. 16.1 Prokaryotes are diverse and widespread Prokaryotes lived alone on Earth for over 1 billion years – They remain the most numerous and widespread organisms on Earth – The total biomass of prokaryotes is ten times that of eukaryotes Copyright © 2009 Pearson Education, Inc. 16.1 Prokaryotes are diverse and widespread Most prokaryotes are 1–5 µm in diameter (vs. 10– 100 µm for eukaryotic cells) More prokaryotes live in your mouth than the total number of humans that have ever lived There are ten times as many prokaryotes living in and on your body as the number of cells in your body Copyright © 2009 Pearson Education, Inc. 16.1 Prokaryotes are diverse and widespread Prokaryotes live in cold, hot, salty, acidic, and alkaline habitats Although some bacteria are pathogenic and cause disease, most bacteria on our bodies are benign or beneficial – Several hundred species of bacteria live in and on our bodies, decomposing dead skin cells, supplying essential vitamins, and guarding against pathogenic organisms Prokaryotes in soil decompose dead organisms, sustaining chemical cycles Copyright © 2009 Pearson Education, Inc. 16.2 Bacteria and archaea are the two main branches of prokaryotic evolution The two prokaryotic domains, Bacteria and Archaea, diverged soon after life on Earth arose Present day Archaea and Eukarya evolved from a common ancestor, complicated by gene transfer between prokaryotic lineages Some genes of Archaea are similar to bacterial genes, some are similar to eukaryotic genes, and some are unique to Archaea Copyright © 2009 Pearson Education, Inc. 16.4 Various structural features contribute to the success of prokaryotes Prokaryotic cell walls maintain cell shape, provide physical protection, and prevent the cell from bursting in a hypotonic environment – In a hypertonic environment, most prokaryotes lose water and shrink away from their wall The cell walls of Archaea and Bacteria differ Video: Prokaryotic Flagella (Salmonella typhimurium) Copyright © 2009 Pearson Education, Inc. 16.4 Various structural features contribute to the success of prokaryotes Bacterial cell walls can be distinguished with a gram stain – Gram-positive bacteria have simple walls with a thick layer of peptidoglycan – Gram-negative bacteria have complex walls with less peptidoglycan and an outer membrane of lipids bonded to carbohydrates Copyright © 2009 Pearson Education, Inc. Capsule 16.4 Various structural features contribute to the success of prokaryotes Some prokaryotes stick to the substrate or each other with hair-like appendages called pili Sex pili join prokaryotes during conjugation Copyright © 2009 Pearson Education, Inc. Pili 16.4 Various structural features contribute to the success of prokaryotes The flagella of Bacteria and Archaea allow them to move in response to chemical and physical signals in their environment The prokaryotic flagellum is a naked protein without microtubules – The flagellum rotates like a propeller Are prokaryotic flagella homologous or analogous to eukaryotic flagella? Copyright © 2009 Pearson Education, Inc. Flagellum Plasma membrane Cell wall Rotary movement of each flagellum 16.4 Various structural features contribute to the success of prokaryotes Some prokaryotes can withstand harsh conditions by forming endospores within an outer cell – The endospore has a thick protective coat – It can dehydrate and is tolerant of extreme heat or cold When conditions improve, the endospore absorbs water and resumes growth, sometimes after centuries Copyright © 2009 Pearson Education, Inc. Endospore 16.4 Various structural features contribute to the success of prokaryotes Some prokaryotic cells have specialized membranes that perform metabolic functions – Aerobic prokaryotes carry out cellular respiration on infoldings of the plasma membrane – Where is cellular respiration carried out in a eukaryote? – Cyanobacteria carry out photosynthesis on infolded thylakoid membranes – Where is photosynthesis carried out in a photosynthetic eukaryote? Copyright © 2009 Pearson Education, Inc. Respiratory membrane Thylakoid membrane 16.4 Various structural features contribute to the success of prokaryotes Prokaryotic DNA forms a circular chromosome – Smaller rings of DNA called plasmids carry genes that may provide resistance to antibiotics or metabolize rare nutrients, among other metabolic activities Many prokaryotes can transfer genes, such as antibiotic resistance genes, within or between species Copyright © 2009 Pearson Education, Inc. Energy source CO2 Light Chemical Photoautotrophs Chemoautotrophs Carbon source Organic Photoheterotrophs Chemoheterotrophs compounds 16.5 Prokaryotes obtain nourishment in a variety of ways In some prokaryotes, metabolic cooperation occurs in surface-coating colonies called biofilms – Biofilms form when cells in a colony secrete signaling molecules that recruit nearby cells – Channels in the biofilm allow nutrients and wastes to move inside and outside the biofilm Biofilms cause ear and urinary tract infections and the dental plaque that produces tooth decay Copyright © 2009 Pearson Education, Inc. 16.6 Archaea thrive in extreme environments— and in other habitats Archaea are among the most abundant cells on Earth They are a major life-form in the oceans Video: Tubeworms Copyright © 2009 Pearson Education, Inc. 16.7 Bacteria include a diverse assemblage of prokaryotes Clades of gram-negative bacteria – Alpha proteobacteria – Rhizobium species live in legume nodules and fix atmospheric N2 – Photosynthetic gamma proteobacteria – Sulfur bacteria oxidize H2S Copyright © 2009 Pearson Education, Inc. 16.7 Bacteria include a diverse assemblage of prokaryotes Clades of gram-negative bacteria – Delta proteobacteria – Myxobacteria form elaborate colonies and congregate into fruiting bodies that release resistant spores – Chlamydias live inside eukaryotic host cells – Chlamydias cause blindness and sexually transmitted disease – Spirochetes are helical bacteria – Spirochetes cause syphilis and Lyme disease Video: Cyanobacteria (Oscillatoria) Copyright © 2009 Pearson Education, Inc. Nitrogen-fixing cells Photosynthetic cells 16.7 Bacteria include a diverse assemblage of prokaryotes Clades of gram-positive bacteria – Actinomycetes are common soil bacteria that decompose organic matter – Streptomyces is a source of many antibiotics – Mycoplasmas lack cell walls – They are the tiniest of all known cells, with diameters as small as 0.1 µm (about 5 times the size of a ribosome) – Cyanobacteria carry out oxygen-generating photosynthesis – Ancient cyanobacteria formed stromatolites that made the atmosphere aerobic Copyright © 2009 Pearson Education, Inc. 16.8 CONNECTION: Some bacteria cause disease Pathogenic bacteria cause disease by producing poisonous exotoxins or endotoxins – Exotoxins are proteins secreted by bacterial cells – Some of the most powerful toxins known are exotoxins, including the toxin that causes lockjaw – Staphylococcus aureus produces several exotoxins, including one that causes deadly toxic shock syndrome Copyright © 2009 Pearson Education, Inc. 16.8 CONNECTION: Some bacteria cause disease Endotoxins are components of the outer membrane of gram-negative bacteria, released when the cell dies or is digested by a defensive cell – Endotoxins produce septic shock, bacterial meningitis, and food poisoning – The most widespread pest-carried disease in the United States is Lyme disease, caused by the spirochaete Borrelia burgdorferi Copyright © 2009 Pearson Education, Inc. Spirochete that causes Lyme disease “Bull’s-eye” rash Tick that carries the Lyme disease bacterium Spirochete that causes Lyme disease Tick that carries the Lyme disease bacterium “Bull’s-eye” rash 16.9 CONNECTION: Bacteria can be used as biological weapons The bacterium that causes anthrax can be used as biological weapons – Bacillus anthracis forms hardy endospores – Weaponizing anthrax involves manufacturing endospores that disperse easily in air, where they are inhaled and germinate in the lungs The Biological Weapons Convention has been signed by 103 nations, who have pledged never to develop or store biological weapons Copyright © 2009 Pearson Education, Inc. 16.10 CONNECTION: Prokaryotes help recycle chemicals and clean up the environment Prokaryotes are key participants in chemical cycles, making nitrogen available to plants and thus animals They also decompose organic wastes and dead organisms to inorganic chemicals Bioremediation is the use of organisms to remove pollutants from soil, air, or water – Prokaryotes are decomposers in sewage treatment and can clean up oil spills and toxic mine wastes Copyright © 2009 Pearson Education, Inc. Rotating spray arm Rock bed coated with aerobic bacteria and fungi Liquid wastes Outflow Rotating spray arm Rock bed coated with aerobic bacteria and fungi Liquid wastes Outflow PROTISTS Copyright © 2009 Pearson Education, Inc. 16.11 Protists are an extremely diverse assortment of eukaryotes Protists constitute several kingdoms within the domain Eukarya Protists obtain their nutrition in a variety of ways – Algae are autotrophic protists – Protozoans are heterotrophic protists, eating bacteria and other protists – Fungus-like protists obtain organic molecules by absorption Copyright © 2009 Pearson Education, Inc. 16.11 Protists are an extremely diverse assortment of eukaryotes Symbiosis is a close association between organisms of two or more species – Endosymbiosis—living within another – Termite endosymbionts digest cellulose in the wood eaten by the host – The protists have endosymbiotic prokaryotes that metabolize the cellulose Copyright © 2009 Pearson Education, Inc. 16.11 Protists are an extremely diverse assortment of eukaryotes Protists are eukaryotes, with – Membrane-bound chromosomes – Multiple chromosomes – Flagella or cilia with 9 + 2 pattern of microtubules Some protists have a very high level of cellular complexity Copyright © 2009 Pearson Education, Inc. 16.12 EVOLUTION CONNECTION: Secondary endosymbiosis is the key to protist diversity What is the origin of the enormous diversity of protists? – Complex eukaryotic cells evolved when prokaryotes took up residence within larger prokaryotes Copyright © 2009 Pearson Education, Inc. Cyanobacterium Primary endosymbiosis Nucleus Heterotrophic eukaryote Evolved into chloroplast Green alga Nucleus Chloroplast Cyanobacterium Primary endosymbiosis Autotrophic eukaryotes Nucleus Heterotrophic eukaryote Evolved into chloroplast Nucleus Chloroplast Red alga Green alga Nucleus Chloroplast Cyanobacterium Primary endosymbiosis Autotrophic eukaryotes Nucleus Heterotrophic eukaryote Evolved into chloroplast Nucleus Chloroplast Red alga Heterotrophic eukaryotes Green alga Nucleus Chloroplast Secondary endosymbiosis Cyanobacterium Primary endosymbiosis Autotrophic eukaryotes Heterotrophic eukaryotes Nucleus Heterotrophic eukaryote Evolved into chloroplast Secondary endosymbiosis Nucleus Chloroplast Red alga Green alga Nucleus Chloroplast Secondary endosymbiosis Remnant of green alga Euglenozoans Cyanobacterium Primary endosymbiosis Autotrophic eukaryotes Heterotrophic eukaryotes Remnant of red alga Nucleus Heterotrophic eukaryote Dinoflagellates Evolved into chloroplast Secondary endosymbiosis Apicomplexans Nucleus Chloroplast Red alga Stramenopiles 16.13 A tentative phylogeny of eukaryotes includes multiple clades of protists The taxonomy of protists remains a work in progress – The names, boundaries, and placement of clades will continue to change as genomes of more protists are sequenced and compared Copyright © 2009 Pearson Education, Inc. Diplomonads Parabasalids Euglenozoans Alveolates Dinoflagellates Apicomplexans Ciliates Stramenopiles Diatoms Brown algae Water molds Forams Radiolarians Red algae Green algae Chlorophytes Charophytes Amoebozoans Land plants Amoebas Slime molds Fungi Choanoflagellates Animals 16.14 Diplomonads and parabasalids have modified mitochondria Diplomonads may be the most ancient surviving lineage of eukaryotes – They have modified mitochondria without DNA or electron transport chains – Most are anaerobic Parabasalids are heterotrophic protists with modified mitochondria that generate some energy anaerobically – The parasite Trichomonas vaginalis is sexually transmitted, feeding on white blood cells and bacteria living in the cells lining the vagina Copyright © 2009 Pearson Education, Inc. Flagella Undulating membrane 16.15 Euglenozoans have flagella with a unique internal structure Euglenozoans are a diverse clade of protists – Their common feature is a crystalline rod of unknown function inside their flagella Euglenozoans include heterotrophs, photosynthetic autotrophs, and pathogenic parasites Video: Euglena Video: Euglena Motion Copyright © 2009 Pearson Education, Inc. 16.16 Alveolates have sacs beneath the plasma membrane Alveolates have membrane-enclosed sacs or alveoli beneath the plasma membrane Dinoflagellates are important members of marine and freshwater phytoplankton – Some live within coral animals, feeding coral reef communities – Dinoflagellate blooms cause red tides Ciliates use cilia to move and feed. Apicomplexans are animal parasites such as Plasmodium, which causes malaria Copyright © 2009 Pearson Education, Inc. 16.16 Alveolates have sacs beneath the plasma membrane Video: Dinoflagellate Video: Paramecium Cilia Video: Paramecium Vacuole Video: Vorticella Cilia Video: Vorticella Detail Video: Vorticella Habitat Copyright © 2009 Pearson Education, Inc. Cilia Macronucleus 16.17 Stramenopiles have “hairy” and smooth flagella Stramenopiles are named for their “hairy” flagellum, usually paired with a “smooth” flagellum – Water molds are fungus-like and decompose dead organisms in freshwater habitats – Diatoms are unicellular, with silicate cell walls – Brown algae are large, complex algae called seaweeds; all are multicellular and most are marine Video: Water Mold Oogonium Video: Diatoms Moving Video: Water Mold Zoospores Video: Various Diatoms Copyright © 2009 Pearson Education, Inc. 16.18 Amoebozoans have lobe-shaped pseudopodia Amoebas move and feed by means of pseudopodia Members of the clade amoebozoans include many free-living amoebas, some parasitic amoebas, and slime molds – All have lobe-shaped pseudopodia Video: Amoeba Video: Plasmodial Slime Mold Streaming Video: Amoeba Pseudopodia Video: Plasmodial Slime Mold Zoom Copyright © 2009 Pearson Education, Inc. 16.18 Amoebozoans have lobe-shaped pseudopodia A plasmodial slime mold is an amoebozoan that forms a plasmodium, a multinucleate mass of cytoplasm – The plasmodium extends pseudopodia through soil and rotting logs, engulfing food by phagocytosis as it grows – Under adverse conditions, the plasmodium forms reproductive structures that produce spores Cellular slime molds live as solitary amoeboid cells – When food is scarce, the amoeboid cells swarm together, forming a slug-like aggregate that migrates, before forming a fruiting body borne on a stalk Copyright © 2009 Pearson Education, Inc. 16.19 Foraminiferans and radiolarians have threadlike pseudopodia Foraminiferans and radiolarians move and feed by means of threadlike pseudopodia Foraminiferans live in marine and freshwater – They have porous tests composed of calcium carbonate, with small pores through which pseudopodia extend Radiolarians produce an internal silicate skeleton – The test is composed of organic materials Copyright © 2009 Pearson Education, Inc. 16.20 Red algae and green algae are the closest relatives of land plants Red algae are typically soft-bodied, but some have cell walls encrusted with hard, chalky deposits Green algae split into two groups, the chlorophytes and the charophytes – The charophytes are the closest living relatives of land plants Copyright © 2009 Pearson Education, Inc. 16.20 Red algae and green algae are the closest relatives of land plants Video: Volvox Falgella Video: Volvox Colony Video: Volvox Daughter Video: Volvox Female Spheroid Video: Chlamydomonas Video: Volvox Inversion 1 Video: Volvox Inversion 2 Video: Volvox Sperm and Female Copyright © 2009 Pearson Education, Inc. Chlamydomonas Volvox colonies 16.20 Red algae and green algae are the closest relatives of land plants The life cycles of most green algae involve the alternation of generations, in which a haploid (n) gametophyte alternates with a diploid (2n) sporophyte generation Copyright © 2009 Pearson Education, Inc. Mitosis Male gametophyte Spores Mitosis Meiosis Gametes Female gametophyte Fusion of gametes Sporophyte Zygote Mitosis Key Haploid (n) Diploid (2n) 16.21 EVOLUTION CONNECTION: Multicellularity evolved several times in eukaryotes Multicellularity evolved in several different lineages, probably by specialization of the cells of colonial protists. – Stramenopile lineage brown algae – Unnamed lineage red algae, green algae, land plants – Opisthokont lineage fungi and animals Multicellular life arose over a billion years ago. By 543 million years ago, diverse animals and multicellular algae lived in aquatic environments; plants and fungi colonized land 500 million years ago Copyright © 2009 Pearson Education, Inc. 1 Unicellular protist Colony Locomotor cells 2 1 Foodsynthesizing cells Unicellular protist Colony Early multicellular organism with specialized, interdependent cells Gamete Locomotor cells 2 1 3 Somatic cells Foodsynthesizing cells Unicellular protist Colony Early multicellular organism with specialized, interdependent cells Later organism that produces gametes Nutritional Mode Energy Source Photoautotroph Sunlight Chemoautotroph Inorganic chemicals Photoheterotroph Sunlight Chemoheterotroph Organic compounds Carbon Source CO2 Organic compounds (a) (b) (c) (d) You should now be able to 1. Compare the characteristics of the three domains of life; explain why biologists consider Archaea to be more closely related to Eukarya than to Bacteria 2. Describe the structures and functions of the diverse features of prokaryotes; explain how these features have contributed to their success 3. Describe the nutritional diversity of prokaryotes; explain the significance of biofilms 4. Describe the diverse types of Archaea living in extreme and moderate environments Copyright © 2009 Pearson Education, Inc. You should now be able to 5. Distinguish between the subgroups of the domain Bacteria, noting the particular structure, special features, and habitats of each group 6. Distinguish between bacterial exotoxins and endotoxins, noting examples of each 7. Describe the positive natural roles of prokaryotes 8. Describe the basic types of protists; explain why biologists currently think that they represent many clades Copyright © 2009 Pearson Education, Inc. You should now be able to 9. Explain how primary endosymbiosis and secondary endosymbiosis led to further cellular diversity 10. Describe the major protist clades noting characteristics and examples of each 11. Describe the life cycle of Ulva, noting each form in the alternation of generations and how each is produced 12. Explain how multicellular life may have evolved in eukaryotes Copyright © 2009 Pearson Education, Inc.