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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
 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.
16.1 Prokaryotes are diverse and widespread
 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
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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
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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
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Energy source
CO2
Light
Chemical
Photoautotrophs
Chemoautotrophs
Carbon
source
Organic
Photoheterotrophs Chemoheterotrophs
compounds
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
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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 9 + 2 pattern of microtubules
 Some protists have a very high level of cellular complexity
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16.11 Protists are an extremely diverse assortment
of eukaryotes
 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
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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
 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)
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
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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
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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
16.14 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
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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
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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
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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
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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
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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
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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
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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
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Chlamydomonas
Volvox
colonies
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.
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
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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.
 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
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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