Transcript Three Domains – Archaea, Bacteria, Eukarya

The Origin and Evolution of Microbial Life:
Prokaryotes and Protists
PROKARYOTES
 16.7 Prokaryotes have inhabited Earth for billions of
years
 Prokaryotes are the oldest life-forms
And remain the most numerous and widespread organisms
Figure 16.7
Colorized SEM 650 

Three Domains – Archaea,
Bacteria, Eukarya
 16.8 Bacteria and archaea are the two main branches of
prokaryotic evolution
 Domains Bacteria and Archaea

Are distinguished on the basis of nucleotide sequences and
other molecular and cellular features
 Differences between Bacteria and Archaea
Table 16.8
 16.9 Prokaryotes come in a variety of shapes
 Prokaryotes may be shaped as
Colorized SEM 12,000 

Figure 16.9A–C
Colorized SEM 3,000 

Spheres (cocci)
Rods (bacilli)
Curves or spirals (vibrio or spirochaete)
Colorized SEM 9,000 

 16.10 Various features contribute to the
success of prokaryotes
I.
External Structures
i. Cell wall
ii. Pili
iii. Flagella
II. Reproduction and adaptation
III. Specialized internal structures
IV. Form colonies
V. Varied methods of obtaining food
 External Structures
 The cell wall
Is one of the most important features of
nearly all prokaryotes
 Is covered by a sticky capsule
Capsule
Figure 16.10A
Colorized TEM 70,000 

 Some prokaryotes

Stick to their substrate with pili
Colorized TEM 16,000 
Pili
Figure 16.10B
Flagellum
Colorized TEM 14,000
 Motility
 Many bacteria and archaea
 Are equipped with flagella, which enable them to
move
Plasma
membrane
Cell wall
Figure 16.10C
Rotary movement of
each flagellum
 Reproduction and Adaptation
 Prokaryotes

Have the potential to reproduce
quickly in favorable environments
 Some prokaryotes can withstand harsh
conditions
 By forming endospores
TEM 34,000 
Endospore
Figure 16.10D
 Internal Organization
 Some prokaryotic cells

Have specialized membranes that perform
metabolic functions
Figure 16.10E
Thylakoid
membrane
TEM 6,000
TEM 45,000
Respiratory
membrane
 16.11 Prokaryotes obtain nourishment in a
variety of ways
 As a group
 Prokaryotes exhibit much more
nutritional diversity than eukaryotes
 Types of Nutrition
 Autotrophs make their own organic
compounds from inorganic sources
 Photoautotrophs harness sunlight for
energy and use CO2 for carbon
 Chemoautotrophs obtain energy from
inorganic chemicals instead of sunlight
 Heterotrophs obtain their carbon atoms
from organic compounds
 Photoheterotrophs can obtain energy
from sunlight
 Chemoheterotrophs are so diverse that
almost any organic molecule can serve as
food for some species
Figure 16.11A
 Nutritional classification of organisms
Table 16.11
 Metabolic Cooperation
 In some prokaryotes
Metabolic cooperation occurs in surfacecoating colonies called biofilms
Figure 16.11B
Colorized SEM 13,000 

 16.12 Archaea thrive in extreme environments
(extremophiles) — and in other habitats
 Archaea are common in
 Salt lakes, acidic hot springs, deep-sea
hydrothermal vents
Figure 16.12A, B
 Archaea are also a major life-form in the ocean
Plankton dispersal
Phytoplankton
 16.13 Bacteria include a diverse assemblage of prokaryotes
 Bacteria are currently organized into several subgroups,

LM 13,000 

Figure 16.13A, B
Colorized TEM 5,000 

including
Proteobacteria
Chlamydias
Spirochetes
Figure 16.13C, D
Nitrogen-fixing
cells
Photosynthetic
cells
LM 650 
Colorized SEM 2,8000 

Gram-positive bacteria
Cyanobacteria, which photosynthesize in
a plantlike way
Colorized SEM 2,800

CONNECTION
 16.14 Some bacteria cause disease
 Pathogenic bacteria cause disease by producing
Exotoxins or endotoxins
SEM 12,000 
Spirochete
that causes
Lyme disease
Figure 16.14A, B
“Bull’s-eye”rash
SEM 2,800

Tick that
carries
the Lyme
disease
bacterium
CONNECTION
 16.15 Bacteria can be used as biological weapons
 Bacteria, such as the species that causes anthrax

Can be used as biological weapons
Figure 16.15
CONNECTION
 16.16 Prokaryotes help recycle chemicals and clean
up the environment
 Bioremediation

Is the use of organisms to clean up pollution
 Prokaryotes are decomposers in

Sewage treatment and can clean up oil
spills and toxic mine wastes
Rotating
spray arm
Rock bed
coated with
aerobic
bacteria
and fungi
Liquid wastes
Figure 16.16A, B
Outflow
PROTISTS
 16.17 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

Probably evolved from infoldings of the
plasma membrane
 Mitochondria and chloroplasts

Probably evolved from aerobic and
photosynthetic endosymbionts,
respectively
Endosymbiotic Theory
Cytoplasm
Plasma
membrane
Ancestral prokaryote
 A model of the origin of eukaryotes
Endoplasmic
Nuclear
reticulum
Nucleus envelope
Membrane infolding
Aerobic heterotrophic
prokaryote
Cell with nucleus and
endomembrane system
Some
cells
Ancestral host cell
Photosynthetic
prokaryote
Endosymbiosis
Mitochondrion Chloroplast
Mitochondrion
Figure 16.17
Photosynthetic
eukaryotic cell
 16.18 Protists are an extremely diverse
Figure 16.18
LM 275 
assortment of eukaryotes
 Protists
 Are mostly unicellular eukaryotes
 Molecular systematics
 Is exploring eukaryotic phylogeny
Alveolates
Stramenopila
Figure 16.19
Ancestral eukaryote
Green algae
Red algae
Animals
Choanoflagellates
Fungi
Plants
Closest algal relatives of plants
Amoebozoa
Cellular slime molds
Plasmodial slime molds
Amoebas
Brown algae
Diatoms
Water molds
Ciliates
Apicomplexans
Dinoflagellates
Euglenozoans
Diplomonads
How are Protists classified?
 16.19 A tentative phylogeny of eukaryotes includes multiple
clades of protists
 The taxonomy of protists
 Is a work in progress
 16.20 Diplomonads and euglenozoans include some
flagellated parasites
 The parasitic Giardia
Is a diplomonad with highly reduced
mitochondria
Figure 16.20A
Colorized SEM 4,000 

 Euglenozoans
Figure 16.20B, C
Colorized SEM 1,300 
Include trypanosomes and Euglena
Colorized SEM 1,300 

 16.21 Alveolates have sacs beneath the plasma
SEM 2,300
membrane and include dinoflagellates,
apicomplexans, and ciliates
 Dinoflagellates
 Are unicellular algae
Figure 16.21A
 Apicomplexans are parasites
Such as Plasmodium, which causes malaria
Apex
Figure 16.21B
Red blood cell
TEM 26,000

 Cilliates

Use cilia to move and feed
Cilia
LM 60
Macronucleus
Figure 16.21C
 16.22 Stramenopiles are named for their
“hairy” flagella and include the water molds,
diatoms, and brown algae
 This clade includes
 Fungus-like water molds
Figure 16.22A
Photosynthetic, unicellular diatoms
Figure 16.22B
LM 400


Brown algae, large complex seaweeds
Figure 16.22C
 16.23 Amoebozoans have pseudopodia and include
amoebas and slime molds
 Amoebas
Figure 16.23A
Move and feed by means of pseudopodia
LM 185 

 A plasmodial slime mold is a multinucleate plasmodium

That forms reproductive structures under adverse conditions
Figure 16.23B
 Cellular slime molds
Have unicellular and multicellular stages
45

Figure 16.23C
Reproductive
structure
15
Amoeboid cells
LM 1,000
Slug-like aggregate
 16.24 Red algae and green algae are the closest relatives
of land plants
 Red algae

Contribute to coral reefs
Figure 16.24A
 Green algae

May be unicellular, colonial, or multicellular
Chlamydomonas
LM 80 
LM 1,200 
Volvox colonies
Figure 16.24B
 The life cycles of many algae

Involve the alternation of haploid gametophyte and
diploid sporophyte generations
Mitosis
Male
gametophyte
Spores
Gametes
Mitosis
Meiosis
Female
gametophyte
Fusion of
gametes
Sporophyte
Zygote
Mitosis
Figure 16.24C
Key
Haploid (n)
Diploid (2n)
 16.25 Multicellularity evolved several times in eukaryotes
 Multicellularity evolved in several different lineages

Probably by specialization of the cells of colonial
protists
Gamete
2
1
Unicellular protist
Figure 16.25
Colony
Locomotor
cells
3
Foodsynthesizing
cells
Early multicellular organism
with specialized, interdependent cells
Somatic
cells
Later organism that
produces gametes
 Multicellular life arose over a billion years ago