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Chapter 16 Microbial Life: Prokaryotes and Protists PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko Figure 16.0_1 Figure 16.0_2 Chapter 16: Big Ideas Prokaryotes Protists Figure 16.0_3 PROKARYOTES © 2012 Pearson Education, Inc. 16.1 Prokaryotes are diverse and widespread Prokaryotic cells are smaller than eukaryotic cells. – Prokaryotes range from 1–5 µm in diameter. – Eukaryotes range from 10–100 µm in diameter. The collective biomass of prokaryotes is at least 10 times that of all eukaryotes. © 2012 Pearson Education, Inc. Figure 16.1 16.1 Prokaryotes are diverse and widespread Prokaryotes live in habitats – too cold, – too hot, – too salty, – too acidic, and – too alkaline for eukaryotes to survive. Some bacteria are pathogens, causing disease. But most bacteria on our bodies are benign or beneficial. © 2012 Pearson Education, Inc. 16.1 Prokaryotes are diverse and widespread 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. © 2012 Pearson Education, Inc. 16.2 External features contribute to the success of prokaryotes Prokaryotic cells have three common cell shapes. – Cocci are spherical prokaryotic cells. They sometimes occur in chains that are called streptococci. – Bacilli are rod-shaped prokaryotes. Bacilli may also be threadlike, or filamentous. – Spiral prokaryotes are like a corkscrew. – Short and rigid prokaryotes are called spirilla. – Longer, more flexible cells are called spirochetes. © 2012 Pearson Education, Inc. Figure 16.2A Cocci Bacilli Spirochete Figure 16.2A_1 Cocci Figure 16.2A_2 Bacilli Figure 16.2A_3 Spirochete 16.2 External features contribute to the success of prokaryotes Nearly all prokaryotes have a cell wall. Cell walls – provide physical protection and – prevent the cell from bursting in a hypotonic environment. When stained with Gram stain, cell walls of bacteria are either – Gram-positive, with simpler cell walls containing peptidoglycan, or – Gram-negative, with less peptidoglycan, and more complex and more likely to cause disease. © 2012 Pearson Education, Inc. Figure 16.2B 16.2 External features contribute to the success of prokaryotes The cell wall of many prokaryotes is covered by a capsule, a sticky layer of polysaccharides or protein. The capsule – enables prokaryotes to adhere to their substrate or to other individuals in a colony and – shields pathogenic prokaryotes from attacks by a host’s immune system. © 2012 Pearson Education, Inc. Figure 16.2C Tonsil cell Capsule Bacterium 16.2 External features contribute to the success of prokaryotes Some prokaryotes have external structures that extend beyond the cell wall. – Flagella help prokaryotes move in their environment. – Hairlike projections called fimbriae enable prokaryotes to stick to their substrate or each other. © 2012 Pearson Education, Inc. Figure 16.2D Flagella Fimbriae 16.3 Populations of prokaryotes can adapt rapidly to changes in the environment Prokaryote population growth – occurs by binary fission, – can rapidly produce a new generation within hours, and – can generate a great deal of genetic variation – by spontaneous mutations, – increasing the likelihood that some members of the population will survive changes in the environment. © 2012 Pearson Education, Inc. 16.3 Populations of prokaryotes can adapt rapidly to changes in the environment The genome of a prokaryote typically – has about one-thousandth as much DNA as a eukaryotic genome and – is one long, circular chromosome packed into a distinct region of the cell. Many prokaryotes also have additional small, circular DNA molecules called plasmids, which replicate independently of the chromosome. © 2012 Pearson Education, Inc. Figure 16.3A Chromosome Plasmids 16.3 Populations of prokaryotes can adapt rapidly to changes in the environment Some prokaryotes form specialized cells called endospores that remain dormant through harsh conditions. Endospores can survive extreme heat or cold. © 2012 Pearson Education, Inc. Figure 16.3B Endospore 16.4 Prokaryotes have unparalleled nutritional diversity Prokaryotes exhibit much more nutritional diversity than eukaryotes. Two sources of energy are used. – Phototrophs capture energy from sunlight. – Chemotrophs harness the energy stored in chemicals. © 2012 Pearson Education, Inc. 16.4 Prokaryotes have unparalleled nutritional diversity Two sources of carbon are used by prokaryotes. – Autotrophs obtain carbon atoms from carbon dioxide. – Heterotrophs obtain their carbon atoms from the organic compounds present in other organisms. © 2012 Pearson Education, Inc. 16.4 Prokaryotes have unparalleled nutritional diversity The terms that describe how prokaryotes obtain energy and carbon are combined to describe their modes of nutrition. – Photoautotrophs obtain energy from sunlight and use carbon dioxide for carbon. – Photoheterotrophs obtain energy from sunlight but get their carbon atoms from organic molecules. – Chemoautotrophs harvest energy from inorganic chemicals and use carbon dioxide for carbon. – Chemoheterotrophs acquire energy and carbon from organic molecules. © 2012 Pearson Education, Inc. Figure 16.4 Sunlight Photoautotrophs Chemicals Chemoautotrophs Oscilliatoria Unidentified “rock-eating” bacteria Photoheterotrophs Chemoheterotrophs Rhodopseudomonas A Bdellovibrio attacking a larger cell CO2 Organic compounds CARBON SOURCE ENERGY SOURCE Figure 16.4_1 Photoautotrophs Oscilliatoria Figure 16.4_2 Photoheterotrophs Rhodopseudomonas Figure 16.4_3 Chemoautotrophs Unidentified “rock-eating” bacteria Figure 16.4_4 Chemoheterotrophs A Bdellovibrio attacking a larger cell 16.5 CONNECTION: Biofilms are complex associations of microbes Biofilms – are complex associations of one or several species of prokaryotes and – may also include protists and fungi. Prokaryotes attach to surfaces and form biofilm communities that – are difficult to eradicate and – may cause medical and environmental problems. © 2012 Pearson Education, Inc. 16.5 CONNECTION: Biofilms are complex associations of microbes Biofilms are large and complex “cities” of microbes that – communicate by chemical signals, – coordinate a division of labor and defense against invaders, and – use channels to distribute nutrients and collect wastes. © 2012 Pearson Education, Inc. 16.5 CONNECTION: Biofilms are complex associations of microbes Biofilms that form in the environment can be difficult to eradicate. Biofilms – clog and corrode pipes, – gum up filters and drains, and – Coat the hulls of ships. © 2012 Pearson Education, Inc. Figure 16.5 16.6 CONNECTION: Prokaryotes help clean up the environment Prokaryotes are useful for cleaning up contaminants in the environment because prokaryotes – have great nutritional diversity, – are quickly adaptable, and – can form biofilms. © 2012 Pearson Education, Inc. 16.6 CONNECTION: Prokaryotes help clean up the environment Bioremediation is the use of organisms to remove pollutants from – soil, – air, or – water. © 2012 Pearson Education, Inc. 16.6 CONNECTION: Prokaryotes help clean up the environment Prokaryotic decomposers are the mainstays of sewage treatment facilities. – Raw sewage is first passed through a series of screens and shredders. – Solid matter then settles out from the liquid waste, forming sludge. – Sludge is gradually added to a culture of anaerobic prokaryotes, including bacteria and archaea. – The microbes decompose the organic matter into material that can be placed in a landfill or used as fertilizer. © 2012 Pearson Education, Inc. 16.6 CONNECTION: Prokaryotes help clean up the environment Liquid wastes are treated separately from the sludge. – Liquid wastes are sprayed onto a thick bed of rocks. – Biofilms of aerobic bacteria and fungi growing on the rocks remove much of the dissolved organic material. – Fluid draining from the rocks is sterilized and then released, usually into a river or ocean. © 2012 Pearson Education, Inc. Figure 16.6A Rotating spray arm Rock bed coated with aerobic prokaryotes and fungi Liquid wastes Outflow Figure 16.6A_1 Rotating spray arm Rock bed coated with aerobic prokaryotes and fungi Liquid wastes Outflow Figure 16.6A_2 Rotating spray arm Rock bed coated with aerobic prokaryotes and fungi 16.6 CONNECTION: Prokaryotes help clean up the environment Bioremediation is becoming an important tool for cleaning up toxic chemicals released into the soil and water by industrial processes. Environmental engineers change the natural environment to accelerate the activity of naturally occurring prokaryotes capable of metabolizing pollutants. © 2012 Pearson Education, Inc. Figure 16.6B 16.7 Bacteria and archaea are the two main branches of prokaryotic evolution New studies of representative genomes of prokaryotes and eukaryotes strongly support the three-domain view of life. – Prokaryotes are now classified into two domains: – Bacteria and – Archaea. – Archaea have at least as much in common with eukaryotes as they do with bacteria. © 2012 Pearson Education, Inc. Table 16.7 16.8 Archaea thrive in extreme environments— and in other habitats Archaeal inhabitants of extreme environments have unusual proteins and other molecular adaptations that enable them to metabolize and reproduce effectively. – Extreme halophiles thrive in very salty places. – Extreme thermophiles thrive in – very hot water, such as geysers, and – acid pools. © 2012 Pearson Education, Inc. Figure 16.8A 16.8 Archaea thrive in extreme environments— and in other habitats Methanogens – live in anaerobic environments, – give off methane as a waste product from – the digestive tracts of cattle and deer and – decomposing materials in landfills. © 2012 Pearson Education, Inc. Figure 16.8B 16.9 Bacteria include a diverse assemblage of prokaryotes The domain Bacteria is currently divided into five groups, based on comparisons of genetic sequences. 1. Proteobacteria – are all gram negative, – share a particular rRNA sequence, and – represent all four modes of nutrition. © 2012 Pearson Education, Inc. 16.9 Bacteria include a diverse assemblage of prokaryotes – Thiomargarita namibiensis is a type of proteobacteria that – is a giant among prokaryotes, typically ranging up to 100–300 microns in diameter, – uses H2S to generate organic molecules from CO2, and – produces sulfur wastes, seen as small greenish globules in the following figure. © 2012 Pearson Education, Inc. Figure 16.9A 16.9 Bacteria include a diverse assemblage of prokaryotes – Proteobacteria also include Rhizobium species that – live symbiotically in root nodules of legumes and – convert atmospheric nitrogen gas into a form usable by their legume host. – Symbiosis is a close association between organisms of two or more species. – Rhizobium is an endosymbiont, living within another species. © 2012 Pearson Education, Inc. Figure 32.13B Shoot Bacteria within vesicle in an infected cell Nodules Roots 16.9 Bacteria include a diverse assemblage of prokaryotes 2. Gram-positive bacteria – rival proteobacteria in diversity and – include the actinomycetes common in soil. – Streptomyces is often cultured by pharmaceutical companies as a source of many antibiotics. © 2012 Pearson Education, Inc. Figure 16.9B 16.9 Bacteria include a diverse assemblage of prokaryotes 3. Cyanobacteria – Cyanobacteria are the only group of prokaryotes with plantlike, oxygen-generating photosynthesis. – Some species, such as Anabaena, have specialized cells that fix nitrogen. © 2012 Pearson Education, Inc. Figure 16.9C Photosynthetic cells Nitrogen-fixing cells 16.9 Bacteria include a diverse assemblage of prokaryotes 4. Chlamydias – Chlamydias live inside eukaryotic host cells. – Chlamydia trachomatis – is a common cause of blindness in developing countries and – is the most common sexually transmitted disease in the United States. © 2012 Pearson Education, Inc. Figure 16.9D 16.9 Bacteria include a diverse assemblage of prokaryotes 5. Spirochetes are – helical bacteria and – notorious pathogens, causing – syphilis and – Lyme disease. © 2012 Pearson Education, Inc. Figure 16.9E 16.10 CONNECTION: Some bacteria cause disease All organisms are almost constantly exposed to pathogenic bacteria. Most bacteria that cause illness do so by producing a poison. – Exotoxins are proteins that bacterial cells secrete into their environment. – Endotoxins are components of the outer membrane of gram-negative bacteria. © 2012 Pearson Education, Inc. Figure 16.10 16.11 SCIENTIFIC DISCOVERY: Koch’s postulates are used to prove that a bacterium causes a disease Koch’s postulates are four essential conditions used to establish that a certain bacterium is the cause of a disease. They are 1. find the bacterium in every case of the disease, 2. isolate the bacterium from a person who has the disease and grow it in pure culture, 3. show that the cultured bacterium causes the disease when transferred to a healthy subject, and 4. isolate the bacterium from the experimentally infected subject. © 2012 Pearson Education, Inc. 16.11 SCIENTIFIC DISCOVERY: Koch’s postulates are used to prove that a bacterium causes a disease Koch’s postulates were used to demonstrate that the bacterium Helicobacter pylori is the cause of most peptic ulcers. The 2005 Nobel Prize in Medicine was awarded to Barry Marshall and Robin Warren for this discovery. © 2012 Pearson Education, Inc. Figure 16.11 16.12 CONNECTION: Bacteria can be used as biological weapons Bacteria that cause anthrax and the plague can be used as biological weapons. – Bacillus anthracis killed five people in the United States in 2001. – Yersinia pestis bacteria – are typically carried by rodents and transmitted by fleas, causing the plague and – can cause a pneumonic form of plague if inhaled. © 2012 Pearson Education, Inc. Figure 16.12 16.12 CONNECTION: Bacteria can be used as biological weapons Clostridium botulinum produces the exotoxin botulinum, the deadliest poison on earth. Botulinum blocks transmission of nerve signals and prevents muscle contraction. © 2012 Pearson Education, Inc. PROTISTS © 2012 Pearson Education, Inc. 16.13 Protists are an extremely diverse assortment of eukaryotes Protists – are a diverse collection of mostly unicellular eukaryotes, – may constitute multiple kingdoms within the Eukarya, and – refer to eukaryotes that are not – plants, – animals, or – fungi. © 2012 Pearson Education, Inc. 16.13 Protists are an extremely diverse assortment of eukaryotes Protists obtain their nutrition in many ways. Protists include – autotrophs, called algae, producing their food by photosynthesis, – heterotrophs, called protozoans, eating bacteria and other protists, – heterotrophs, called parasites, deriving their nutrition from a living host, and – mixotrophs, using photosynthesis and heterotrophy. © 2012 Pearson Education, Inc. Figure 16.13A Autotrophy Caulerpa, a green alga Heterotrophy Giardia, a parasite Mixotrophy Euglena Figure 16.13A_1 Autotrophy Caulerpa, a green alga Figure 16.13A_2 Heterotrophy Giardia, a parasite Figure 16.13A_3 Mixotrophy Euglena 16.13 Protists are an extremely diverse assortment of eukaryotes Protists are found in many habitats including – anywhere there is moisture and – the bodies of host organisms. © 2012 Pearson Education, Inc. Figure 16.13B Figure 16.13B_1 Figure 16.13B_2 16.13 Protists are an extremely diverse assortment of eukaryotes Recent molecular and cellular studies indicate that nutritional modes used to categorize protists do not reflect natural clades. Protist phylogeny remains unclear. One hypothesis, used here, proposes five monophyletic supergroups. © 2012 Pearson Education, Inc. 16.14 EVOLUTION CONNECTION: Secondary endosymbiosis is the key to much of protist diversity The endosymbiont theory explains the origin of mitochondria and chloroplasts. – Eukaryotic cells evolved when prokaryotes established residence within other, larger prokaryotes. – This theory is supported by present-day mitochondria and chloroplasts that – have structural and molecular similarities to prokaryotic cells and – replicate and use their own DNA, separate from the nuclear DNA of the cell. © 2012 Pearson Education, Inc. Figure 16.14_s1 Primary endosymbiosis Evolved into Cyanobacterium chloroplast 2 Nucleus Heterotrophic eukaryote 1 Figure 16.14_s2 Primary endosymbiosis Green alga Chloroplast Evolved into Cyanobacterium chloroplast 2 3 Nucleus Heterotrophic eukaryote 1 Autotrophic eukaryotes Chloroplast Red alga Figure 16.14_s3 Primary endosymbiosis Green alga Chloroplast Evolved into Cyanobacterium chloroplast 2 3 Nucleus Heterotrophic eukaryote 1 Autotrophic eukaryotes Chloroplast Red alga 4 Heterotrophic eukaryotes 16.14 EVOLUTION CONNECTION: Secondary endosymbiosis is the key to much of protist diversity Secondary endosymbiosis is – the process in which an autotrophic eukaryotic protist became endosymbiotic in a heterotrophic eukaryotic protist and – key to protist diversity. © 2012 Pearson Education, Inc. Figure 16.14_s4 Primary endosymbiosis Secondary endosymbiosis Green alga Chloroplast Evolved into Cyanobacterium chloroplast 2 3 Nucleus Heterotrophic eukaryote 1 Autotrophic eukaryotes Chloroplast Red alga 4 Heterotrophic eukaryotes 5 Figure 16.14_s5 Primary endosymbiosis Secondary endosymbiosis Green alga Remnant of green alga Chloroplast Evolved into Cyanobacterium chloroplast Euglena 2 3 Nucleus Heterotrophic eukaryote 1 Autotrophic eukaryotes Chloroplast Red alga 4 Heterotrophic eukaryotes 5 16.15 Chromalveolates represent the range of protist diversity Chromalveolates include – diatoms, unicellular algae with a glass cell wall containing silica, © 2012 Pearson Education, Inc. Figure 16.15A 16.15 Chromalveolates represent the range of protist diversity Chromalveolates include – diatoms, unicellular algae with a glass cell wall containing silica, – dinoflagellates, unicellular autotrophs, heterotrophs, and mixotrophs that are common components of marine plankton, © 2012 Pearson Education, Inc. Figure 16.15B 16.15 Chromalveolates represent the range of protist diversity Chromalveolates include – diatoms, unicellular algae with a glass cell wall containing silica, – dinoflagellates, unicellular autotrophs, heterotrophs, and mixotrophs that are common components of marine plankton, – brown algae, large, multicellular autotrophs, © 2012 Pearson Education, Inc. Figure 16.15C 16.15 Chromalveolates represent the range of protist diversity Chromalveolates include – diatoms, unicellular algae with a glass cell wall containing silica, – dinoflagellates, unicellular autotrophs, heterotrophs, and mixotrophs that are common components of marine plankton, – brown algae, large, multicellular autotrophs, – water molds, unicellular heterotrophs, © 2012 Pearson Education, Inc. Figure 16.15D 16.15 Chromalveolates represent the range of protist diversity Chromalveolates include – diatoms, unicellular algae with a glass cell wall containing silica, – dinoflagellates, unicellular autotrophs, heterotrophs, and mixotrophs that are common components of marine plankton, – brown algae, large, multicellular autotrophs, – water molds, unicellular heterotrophs, – ciliates, unicellular heterotrophs and mixotrophs that use cilia to move and feed, © 2012 Pearson Education, Inc. Figure 16.15E Mouth 16.15 Chromalveolates represent the range of protist diversity Chromalveolates include – diatoms, unicellular algae with a glass cell wall containing silica, – dinoflagellates, unicellular autotrophs, heterotrophs, and mixotrophs that are common components of marine plankton, – brown algae, large, multicellular autotrophs, – water molds, unicellular heterotrophs, – ciliates, unicellular heterotrophs and mixotrophs that use cilia to move and feed, and – a group including parasites, such as Plasmodium, which causes malaria. © 2012 Pearson Education, Inc. 16.16 CONNECTION: Can algae provide a renewable source of energy? Fossil fuels – are the organic remains of organisms that lived hundreds of millions of years ago and – primarily consist of – diatoms and – primitive plants. © 2012 Pearson Education, Inc. 16.16 CONNECTION: Can algae provide a renewable source of energy? Lipid droplets in diatoms and other algae may serve as a renewable source of energy. If unicellular algae could be grown on a large scale, this oil could be harvested and processed into biodiesel. Numerous technical hurdles remain before industrial-scale production of biofuel from algae becomes a reality. © 2012 Pearson Education, Inc. Figure 16.16 16.17 Rhizarians include a variety of amoebas The two largest groups of Rhizaria are among the organisms referred to as amoebas. Amoebas move and feed by means of pseudopodia, temporary extensions of the cell. © 2012 Pearson Education, Inc. 16.17 Rhizarians include a variety of amoebas Foraminiferans – are found in the oceans and in fresh water, – have porous shells, called tests, composed of calcium carbonate, and – have pseudopodia that function in feeding and locomotion. © 2012 Pearson Education, Inc. Figure 16.17A Figure 16.17A_1 Figure 16.17A_2 16.17 Rhizarians include a variety of amoebas Radiolarians – are mostly marine and – produce a mineralized internal skeleton made of silica. © 2012 Pearson Education, Inc. Figure 16.17B 16.18 Some excavates have modified mitochondria Excavata has recently been proposed as a clade on the basis of molecular and morphological similarities. The name refers to an “excavated” feeding groove possessed by some members of the group. Excavates – have modified mitochondria that lack functional electron transport chains and – use anaerobic pathways such as glycolysis to extract energy. © 2012 Pearson Education, Inc. 16.18 Some excavates have modified mitochondria Excavates include – heterotrophic termite endosymbionts © 2012 Pearson Education, Inc. Figure 16.13B 16.18 Some excavates have modified mitochondria Excavates include – heterotrophic termite endosymbionts, – autotrophic species, – mixotrophs such as Euglena © 2012 Pearson Education, Inc. Figure 16.13A_3 Mixotrophy Euglena 16.18 Some excavates have modified mitochondria Excavates include – heterotrophic termite endosymbionts, – autotrophic species, – mixotrophs such as Euglena, – the common waterborne parasite Giardia intestinalis, © 2012 Pearson Education, Inc. Figure 16.13A Autotrophy Caulerpa, a green alga Heterotrophy Giardia, a parasite Mixotrophy Euglena 16.18 Some excavates have modified mitochondria Excavates include – heterotrophic termite endosymbionts, – autotrophic species, – mixotrophs such as Euglena, – the common waterborne parasite Giardia intestinalis, – the parasite Trichomonas vaginalis, which causes 5 million new infections each year of human reproductive tracts, © 2012 Pearson Education, Inc. Figure 16.18A Flagella Undulating membrane 16.18 Some excavates have modified mitochondria Excavates include – heterotrophic termite endosymbionts, – autotrophic species, – mixotrophs such as Euglena, – the common waterborne parasite Giardia intestinalis, – the parasite Trichomonas vaginalis, which causes 5 million new infections each year of human reproductive tracts, and – the parasite Trypanosoma, which causes sleeping sickness in humans. © 2012 Pearson Education, Inc. Figure 16.18B 16.19 Unikonts include protists that are closely related to fungi and animals Unikonta is a controversial grouping joining – amoebozoans and – a group that includes animals and fungi, addressed at the end of this unit on protists. © 2012 Pearson Education, Inc. 16.19 Unikonts include protists that are closely related to fungi and animals Amoebozoans have lobe-shaped pseudopodia and include – many species of free-living amoebas, – some parasitic amoebas, and – slime molds. © 2012 Pearson Education, Inc. Figure 16.19A 16.19 Unikonts include protists that are closely related to fungi and animals Plasmodial slime molds – are common where there is moist, decaying organic matter and – consist of a single, multinucleate mass of cytoplasm undivided by plasma membranes, called a plasmodium. © 2012 Pearson Education, Inc. Figure 16.19B Figure 16.19B_1 Figure 16.19B_2 16.19 Unikonts include protists that are closely related to fungi and animals Cellular slime molds – are common on rotting logs and decaying organic matter and – usually exist as solitary amoeboid cells, but when food is scarce, amoeboid cells – swarm together, forming a slug-like aggregate that wanders around for a short time and then – forms a stock supporting an asexual reproductive structure that produces spores. © 2012 Pearson Education, Inc. Figure 16.19C 16.20 Archaeplastids include red algae, green algae, and land plants Archaeplastids include: – red algae, – green algae, and – land plants. © 2012 Pearson Education, Inc. 16.20 Archaeplastids include red algae, green algae, and land plants Red algae – are mostly multicellular, – contribute to the structure of coral reefs, and – are commercially valuable. © 2012 Pearson Education, Inc. Figure 16.20A 16.20 Archaeplastids include red algae, green algae, and land plants Green algae may be unicellular, colonial, or multicellular. – Volvox is a colonial green algae, and – Chlamydomonas is a unicellular alga propelled by two flagella. © 2012 Pearson Education, Inc. Figure 16.20B Volvox Chlamydomonas Figure 16.20B_1 Volvox Figure 16.20B_2 Chlamydomonas 16.20 Archaeplastids include red algae, green algae, and land plants Ulva, or sea lettuce, is – a multicellular green alga with – a complex life cycle that includes an alternation of generations that consists of – a multicellular diploid (2n) form, the sporophyte, that alternates with – a multicellular haploid (1n) form, the gametophyte. © 2012 Pearson Education, Inc. Figure 16.20C_s1 Mitosis Male gametophyte Spores Mitosis Gametes Female gametophyte Key Haploid (n) Diploid (2n) Figure 16.20C_s2 Mitosis Male gametophyte Spores Mitosis Gametes Female gametophyte Fusion of gametes Zygote Key Haploid (n) Diploid (2n) Figure 16.20C_s3 Mitosis Male gametophyte Spores Mitosis Meiosis Gametes Female gametophyte Fusion of gametes Sporophyte Zygote Mitosis Key Haploid (n) Diploid (2n) Figure 16.20C_2 16.21 EVOLUTION CONNECTION: Multicellularity evolved several times in eukaryotes The origin of the eukaryotic cell led to an evolutionary radiation of new forms of life. Unicellular protists are much more diverse in form than simpler prokaryotes. © 2012 Pearson Education, Inc. 16.21 EVOLUTION CONNECTION: Multicellularity evolved several times in eukaryotes Multicellular organisms (seaweeds, plants, animals, and most fungi) are fundamentally different from unicellular organisms. – A multicellular organism has various specialized cells that perform different functions and are interdependent. – All of life’s activities occur within a single cell in unicellular organisms. © 2012 Pearson Education, Inc. 16.21 EVOLUTION CONNECTION: Multicellularity evolved several times in eukaryotes Multicellular organisms have evolved from three different lineages: – brown algae evolved from chromalveolates, – fungi and animals evolved from unikonts, and – red algae and green algae evolved from achaeplastids. © 2012 Pearson Education, Inc. Figure 16.21A Green algae Other green algae Charophytes Land plants Amoebozoans Unikonts Ancestral eukaryote Archaeplastids Red algae Nucleariids Fungi Choanoflagellates Key All unicellular Both unicellular and multicellular All multicellular Animals 16.21 EVOLUTION CONNECTION: Multicellularity evolved several times in eukaryotes One hypothesis states that two separate unikont lineages led to fungi and animals, diverging more than 1 billion years ago. A combination of morphological and molecular evidence suggests that choanoflagellates are the closest living protist relative of animals. © 2012 Pearson Education, Inc. Figure 16.21B Nucleariids Fungi A nucleariid, closest living protistan relative of fungi 1 billion years ago Individual choanoflagellate Choanoflagellates Colonial choanoflagellate Sponge collar cell Animals Sponge Figure 16.21B_1 Nucleariids Fungi A nucleariid, closest living protistan relative of fungi Figure 16.21B_2 Individual choanoflagellate Choanoflagellates Colonial choanoflagellate Sponge collar cell Animals Sponge Figure 16.21B_3 You should now be able to 1. Describe the structures and functions of the diverse features of prokaryotes; explain how these features have contributed to their success. 2. Explain how populations of prokaryotes can adapt rapidly to changes in their environment. 3. Describe the nutritional diversity of prokaryotes and explain the significance of biofilms. 4. Explain how prokaryotes help clean up the environment. 5. Compare the characteristics of the three domains of life; explain why biologists consider Archaea to be more closely related to Eukarya than to Bacteria. © 2012 Pearson Education, Inc. You should now be able to 6. Describe the diverse types of Archaea living in extreme and moderate environments. 7. Distinguish between the subgroups of the domain Bacteria, noting the particular structure, special features, and habitats of each group. 8. Distinguish between bacterial exotoxins and endotoxins, noting examples of each. 9. Describe the steps of Koch’s postulates and explain why they are used. 10. Explain how bacteria can be used as biological weapons. © 2012 Pearson Education, Inc. You should now be able to 11. Describe the extremely diverse assortment of eukaryotes. 12. Explain how primary endosymbiosis and secondary endosymbiosis led to further cellular diversity. 13. Describe the major protist clades noting characteristics and examples of each. 14. Describe the life cycle of Ulva, noting each form in the alternation of generations and how each is produced. 15. Explain how multicellular life may have evolved in eukaryotes. © 2012 Pearson Education, Inc. Figure 16.UN01 Nutritional mode Energy source Photoautotroph Sunlight Chemoautotroph Inorganic chemicals Photoheterotroph Sunlight Chemoheterotroph Organic compounds Carbon source CO2 Organic compounds Figure 16.UN02 Exotoxin Secreted by cell Endotoxin Component of gramnegative plasma membrane Staphylococcus aureus Salmonella enteritidis Figure 16.UN02_1 Exotoxin Secreted by cell Staphylococcus aureus Figure 16.UN02_2 Endotoxin Component of gramnegative plasma membrane Salmonella enteritidis Figure 16.UN03 (a) Red algae Green algae (b) Land plants (c) Ancestral eukaryote Other green algae Amoebozoans Nucleariids (d) (e) (f)