CHAPTER 16 The Origin and Evolution of Microbial Life: Prokaryotes and Protists

1. CHAPTER 16The Origin and Evolution of Microbial Life: Prokaryotes and Protists

2. How Ancient Bacteria Changed the World • Biological and geologic history are closely intertwined • Fossilized mats of prokaryotes 2.5 billion years old mark a time when photosynthetic bacteria were producing O2that made the atmosphere aerobic • These fossilized mats are called stromatolites

3. EARLY EARTH AND THE ORIGIN OF LIFE 16.1 Life began on a young Earth • Planet Earth formed some 4.6 billion years ago

4. Volcanic activity, lightning, and UV radiation were intense • The early atmosphere probably contained H2O, CO, CO2, N2, and possibly some CH4, but little or no O2 Figure 16.1A

5. Fossilized prokaryotes date back 3.5 billion years Figure 16.1B, D

6. = 500 million years ago Earliest animals; diverse algae Earliest multicellular eukaryotes? • Life may have developed from nonliving materials as early as 3.9 billion years ago Earliest eukaryotes Accumulation of atmospheric O2 from photosyntheticcyanobacteria Billions of years ago Oldest known prokaryotic fossils Origin of life? Figure 16.1C Formation of Earth

7. 16.2 How did life originate? • Small organic molecules must have appeared first • This probably happened when inorganic chemicals were energized by lightning or UV radiation

8. 16.3 Talking About Science: Stanley Miller’s experiments showed that organic materials could have arisen on a lifeless earth Figure 16.3A

9. CH4 Water vapor Electrode NH3 H2 • Simulations of such conditions have produced amino acids, sugars, and nucleotide bases Condenser Coldwater Cooled watercontainingorganiccompounds H2O Sample forchemical analysis Figure 16.3B

10. 16.4 The first polymers may have formed on hot rocks or clay • These molecules could have polymerized on hot rocks or clay • This could have produced polypeptides and short nucleic acids

11. 16.5 The first genetic material and enzymes may both have been RNA • The first genes may have been RNA molecules • These molecules could have catalyzed their own replication in a prebiotic RNA world 2 Assembly of acomplementary RNAchain, the first step inreplication of theoriginal “gene” 1 Monomers Formation of short RNApolymers: simple “genes” Figure 16.5

12. 16.6 Molecular cooperatives enclosed by membranes probably preceded the first real cells RNA Self-replicationof RNA • These molecules might have acted as rough templates for the formation of polypeptides • These polypeptides may have in turn assisted RNA replication Self-replicating RNAacts as template onwhich polypeptideforms. Polypeptide Polypeptide actsas primitiveenzyme thataids RNAreplication. Figure 16.6A

13. Surrounding membranes may have protected some of these molecular co-ops as they evolved rudimentary metabolism • Natural selection would have favored the most efficient co-ops • These may have evolved into the first prokaryotic cells

14. Membrane RNA Polypeptide Figure 16.6B, C

15. PROKARYOTES 16.7 Prokaryotes have inhabited Earth for billions of years • Prokaryotes are the oldest life-forms • They remain the most numerous and widespread organisms on Earth today Figure 16.7

16. 16.8 Archaea and bacteria are the two main branches of prokaryotic evolution • Prokaryotes are cells that lack nuclei and other membrane-enclosed organelles

17. Prokaryotes are classified into two domains, based on nucleotide sequences and other features • Bacteria and Archaea Table 16.8

18. 16.9 Prokaryotes come in a variety of shapes • Spheres (cocci) are the most common • Rods (bacilli) • Curves or spirals Figure 16.9A-C

19. 16.10 Prokaryotes obtain nourishment in a variety of ways • These E. Coli colonies are growing with only glucose as an organic nutrient Figure 16.10

20. Photoautotrophs and chemoautotrophs • Heterotrophs obtain carbon from organic compounds • Photo-heterotrophs and chemo-heterotrophs • Autotrophs obtain carbon from CO2 and are of two types Table 16.10

21. They may have gotten their energy from sulfur and iron compounds • The first cells were most likely chemoautotrophs

22. 16.11 Archaea thrive in extreme environments—and in the ocean • Archaea live in • anaerobic swamps • salt lakes • acidic hot springs • deep-sea hydrothermal vents • animal digestive systems Figure 16.11A, B

23. 16.12 Diverse structural features help prokaryotes thrive almost everywhere • Rotating flagella aid in locomotion Flagellum Plasmamembrane Cell wall Rotary movements ofeach flagellum Figure 16.12A

24. Pili help cells cling to surfaces Pili Figure 16.12B

25. Endospores allow certain bacteria to survive environmental extremes in a resting stage Endospore Figure 16.12C

26. Many prokaryotes grow in linear filaments Figure 16.12D

27. 16.13 Connection: Cyanobacteria sometimes “bloom” in aquatic environments • These bacteria photosynthesize in a plant-like way • They often “bloom” in polluted water Figure 16.13A, B

28. 16.14 Connection: Some bacteria cause disease • Pathogenic bacteria can cause disease by producing • exotoxins, such as Staphylococcus aureus • endotoxins • Lyme disease is caused by a bacterium carried by ticks Figure 16.14A, B

29. 16.15 Connection: Koch’s postulates are used to identify disease-causing bacteria • In 1876, Robert Koch discovered rod-shaped bacteria in the blood of cattle suffering from anthrax Figure 16.15A

30. Diseased animal Colony Suspected pathogen(from animal) grownin pure culture • Koch’s postulates are a set of criteria that can prove that bacteria are the cause of disease Bacterium identified Bacteria (pure culture of suspectedpathogen) injected into healthy animal Disease occursin second animal Bacteria from animalgrown in pure culture Identical bacteriumidentified: the pathogen Figure 16.15B

31. 16.16 Connection: Bacteria can be used as biological weapons • The species that causes anthrax can be used as a biological weapon in war or in acts of terrorism Figure 16.16

32. 16.17 Connection: Prokaryotes help recycle chemicals and clean up the environment • Many prokaryotes are environmentally important in Earth’s chemical cycles • We exploit decomposers in sewage treatment Rotatingspray arm Rock bedcoating withaerobicbacteriaand fungi Liquid wastes Outflow Figure 16.17A

33. Prokaryotes hold a great potential for solving environmental problems such as oil spills and toxic mine wastes Figure 16.17B

34. PROTISTS 16.18 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 of eukaryotes probably evolved from infoldings of the plasma membrane of ancestral prokaryotes Plasma membrane Endoplasmic reticulum Nucleus Cytoplasm Nuclearenvelope Figure 16.18A Ancestral prokaryote Cell with nucleus and endomembrane system

35. Mitochondria and chloroplasts probably evolved from symbiotic prokaryotes that took up residence inside larger prokaryotic cells Aerobic heterotrophicprokaryote Mitochondrion Mitochondrion Photosyntheticprokaryote Chloroplast Somecells Ancestral host cell Photosyntheticeukaryotic cell Figure 16.18B

36. 16.19 Protists—unicellular eukaryotes and their close multicellular relatives—probably represent multiple kingdoms • Early protists were the ancestors of plants, animals, and fungi • The taxonomy of protists is in a state of flux Figure 16.19

37. 16.20 Protozoa are protists that ingest their food • They include • flagellates • amoebas Figure 16.20A, B

38. apicomplexans Red blood cell Apex • ciliates Cilia Cilia Macronucleus Macronucleus Figure 16.20C, D

39. Some live in humans and other animals and cause disease • Most protozoa live freely in water or moist soil

40. 16.21 Cellular slime molds have both unicellular and multicellular stages Amoeboidcells • Slime molds are protists that may constitute a distinct kingdom Sluglike colony Reproductivestructure Figure 16.21

41. 16.22 Plasmodial slime molds form brightly colored “supercells” with many nuclei • These slime molds have unicellular stages • They also have stages where they exist as plasmodia, multinuclear masses of cytoplasm undivided by membranes Figure 16.22A, B

42. 16.23 Photosynthetic protists are called algae • They include • Unicellular dinoflagellates Flagellargroove Flagellum Figure 16.23A

43. Diatoms • Green algae Figure 16.23 B, C

44. 16.24 Seaweeds are multicellular marine algae • These protists are multicellular photosynthetic organisms that lack the structural specializations of plants • Examples include • Brown algae • Red algae • Green algae Figure 16.24A, B

45. These groups may eventually be classified with some other groups of protists in a separate kingdom • Many biologists favor classifying red algae in their own kingdom • Brown algae seem closely related to diatoms Macronucleus

46. Their life cycles involve the alternation of generations • Green algae are often classified in the plant kingdom Mitosis Malegametophyte Spores Mitosis Gametes Femalegametophyte HAPLOID (n) Meiosis Fusion of gametes DIPLOID (2n) Mitosis Zygote Sporophyte Macronucleus Figure 16.24C

47. 16.25 Multicellular life may have evolved from colonial protists • Multicellularity evolved independently many times • Probably by specialization of the cells of colonial protists Gamete Locomotorcells 1 2 3 Somaticcells Food-synthesizingcells Unicellularprotist Colony Early multicellular organism withspecialized, interdependent cells Later organism thatproduces gametes Figure 16.25

48. 16.26 Multicellular life has diversified over hundreds of millions of years Multicellular organismscolonize land PALEOZOICERA Diverse multicellular algae, fungi,and animals, all living in the sea • Multicellular life first arose over a billion years ago • All life was aquatic until almost 500 million years ago Mass extinctions Earliest animals; manymulticellular algae Age of fossils in millions of years Oldest known fossils ofmulticellular eukaryotes(small algae) PRECAMBRIAN ERA Earliest multicellular eukaryotes? Figure 16.26