 Biologists classify organisms into three basic Domains  Bacteria and Archaea which are the two domains of the Prokaryotic group  Eukarya which contains all the eukaryotes like plants, fungi, animals and protists

Introduction: How Ancient Bacteria Changed the World Copyright © 2009 Pearson Education, Inc.  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 O 2 and made Earth’s atmosphere aerobic

 Prokaryotes (simple cells that do not have a nucleus like bacteria) lived alone on Earth for over 1 billion years –They remain the most numerous and widespread organisms on Earth  Most prokaryotes are 1–5 µm in diameter (vs. 10– 100 µm for eukaryotic cells)  There are ten times as many prokaryotes living in and on your body as the number of cells in your body 16.1 Prokaryotes are diverse and widespread Copyright © 2009 Pearson Education, Inc.

 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 Prokaryotes are diverse and widespread

 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 16.2 Bacteria and archaea are the two main branches of prokaryotic evolution Copyright © 2009 Pearson Education, Inc.

CO 2 Organic compounds Energy source Chemical Chemoautotrophs Photoautotrophs ChemoheterotrophsPhotoheterotrophs Light Carbon source

 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 CONNECTION: Prokaryotes help recycle chemicals and clean up the environment Copyright © 2009 Pearson Education, Inc.

PROTISTS  Protists are eukaryotes, many are unicellular but some are also multicellular. Some eukaryotic features that all protists share –Membrane-bound nucleus –Flagella or cilia with pattern of microtubules  Some protists have a very high level of cellular complexity Copyright © 2009 Pearson Education, Inc.

 Protists constitute several kingdoms within the domain Eukarya  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 Protists are an extremely diverse assortment of eukaryotes Copyright © 2009 Pearson Education, Inc.

Diplomonads Water molds Parabasalids Euglenozoans Dinoflagellates Apicomplexans Ciliates Brown algae Diatoms Forams Radiolarians Red algae Chlorophytes Charophytes Land plants Green algae Amoebas Slime molds Fungi Choanoflagellates Animals Alveolates Amoebozoans Stramenopiles

 Protists obtain their nutrition in a variety of ways –Algae are autotrophic protists –Protozoans like amoeba, paramecium are heterotrophic protists, eating bacteria and other protists –Fungus-like protists (oomycetes) obtain organic molecules by absorption –Protists are also parasites and pathogenic (Plasmodium, Trypanosome) –Or they can be Symbionts (living in the host without any a harm)

 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 Protists are an extremely diverse assortment of eukaryotes

 What is the origin of the enormous diversity of protists? –Complex eukaryotic cells evolved when prokaryotes took up residence within larger prokaryotes EVOLUTION CONNECTION: Secondary endosymbiosis is the key to protist diversity Copyright © 2009 Pearson Education, Inc.

Nucleus Primary endosymbiosis Cyanobacterium Heterotrophic eukaryote Evolved into chloroplast

Nucleus Primary endosymbiosis Cyanobacterium Heterotrophic eukaryote Evolved into chloroplast Autotrophic eukaryotes Nucleus Chloroplast Green alga Chloroplast Red alga

Nucleus Primary endosymbiosis Cyanobacterium Heterotrophic eukaryote Evolved into chloroplast Autotrophic eukaryotes Nucleus Chloroplast Green alga Chloroplast Red alga Heterotrophic eukaryotes

Nucleus Primary endosymbiosis Cyanobacterium Heterotrophic eukaryote Evolved into chloroplast Autotrophic eukaryotes Nucleus Chloroplast Green alga Chloroplast Red alga Heterotrophic eukaryotes Secondary endosymbiosis Secondary endosymbiosis

Nucleus Primary endosymbiosis Cyanobacterium Heterotrophic eukaryote Evolved into chloroplast Autotrophic eukaryotes Nucleus Chloroplast Green alga Chloroplast Red alga Heterotrophic eukaryotes Secondary endosymbiosis Secondary endosymbiosis Remnant of green alga Euglenozoans Remnant of red alga Dinoflagellates Apicomplexans Stramenopiles

 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 Diplomonads and parabasalids have modified mitochondria Copyright © 2009 Pearson Education, Inc.

Undulating membrane Flagella

 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 Euglenozoans have flagella with a unique internal structure Copyright © 2009 Pearson Education, Inc. Video: Euglena Motion Video: Euglena

 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 Alveolates have sacs beneath the plasma membrane 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

 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 Stramenopiles have “hairy” and smooth flagella Copyright © 2009 Pearson Education, Inc. Video: Water Mold Oogonium Video: Water Mold Zoospores Video: Diatoms Moving Video: Various Diatoms

 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 Amoebozoans have lobe-shaped pseudopodia Copyright © 2009 Pearson Education, Inc. Video: Plasmodial Slime Mold Streaming Video: Plasmodial Slime Mold Zoom Video: Amoeba Video: Amoeba 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 Amoebozoans have lobe-shaped 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 Foraminiferans and radiolarians have threadlike pseudopodia Copyright © 2009 Pearson Education, Inc.

 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 Red algae and green algae are the closest relatives of land plants Copyright © 2009 Pearson Education, Inc.

16.20 Red algae and green algae are the closest relatives of land plants Video: Chlamydomonas Video: Volvox Colony Video: Volvox Daughter Video: Volvox Female Spheroid Video: Volvox Falgella Video: Volvox Inversion 1 Video: Volvox Sperm and Female Video: Volvox Inversion 2

Volvox colonies Chlamydomonas

General Biology of the Protists  Most protists practice both asexual and sexual reproduction; some groups practice only asexual. Asexual reproductive processes in the protists include binary fission, multiple fission, budding, and the formation of spores. Sexual reproduction in the protists also takes various forms.

 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 Red algae and green algae are the closest relatives of land plants

Female gametophyte Gametes Key Fusion of gametes Male gametophyte Meiosis Spores Mitosis Sporophyte Zygote Mitosis Haploid (n) Diploid (2n)

 Multicellularity evolved in several different lineages, probably by specialization of the cells of colonial protists.  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 EVOLUTION CONNECTION: Multicellularity evolved several times in eukaryotes Copyright © 2009 Pearson Education, Inc.

Unicellular protist Colony 1

Unicellular protist Colony 1 Locomotor cells Early multicellular organism with specialized, interdepen- dent cells Food- synthesizing cells 2

Unicellular protist Colony 1 Locomotor cells Early multicellular organism with specialized, interdepen- dent cells Food- synthesizing cells 2 Later organism that produces gametes Somatic cells Gamete 3