Download Protists

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
Chapter 16: Big Ideas
Prokaryotes
Protists
PROKARYOTES
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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.
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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.
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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.
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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.
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Cocci
Bacilli
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.
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Cell
wall
Peptidoglycan
layer
Plasma membrane
Protein
(a) Gram-positive: peptidoglycan traps crystal violet.
Carbohydrate portion
of lipopolysaccharide
Outer
membrane
Cell
wall Peptidoglycan
layer
Plasma membrane
Protein
(b) Gram-negative: crystal violet is easily rinsed away,
revealing red dye.
Grampositive
bacteria
Gramnegative
bacteria
20 µm
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.
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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.
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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.
Prokaryotic chromosomes
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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.
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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.
Endospore
0.3 µm
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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.
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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.
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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.
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Energy source
CO2
Light
Chemical
Photoautotrophs
Chemoautotrophs
Carbon
source
Organic
compounds
Photoheterotrophs Chemoheterotrophs
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.
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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.
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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.
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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.
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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.
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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.
Photosynthetic
cells
Nitrogen-fixing
cells
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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.
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16.9 Bacteria include a diverse assemblage of
prokaryotes
§ 5. Spirochetes are
– helical bacteria and
– notorious pathogens, causing
– syphilis and
– Lyme disease.
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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.
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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.
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PROTISTS
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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.
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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.
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Autotrophy
Caulerpa, a green alga
Heterotrophy
Giardia, a parasite
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.
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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.
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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.
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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.
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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,
– 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.
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16.17 Rhizarians include a variety of amoebas
§ The two largest groups of Rhizaria are
foraminiferans and radiolarians.
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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.
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16.17 Rhizarians include a variety of amoebas
§ Radiolarians
– are mostly marine and
– produce a mineralized internal skeleton made of silica.
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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.
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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.
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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.
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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.
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16.20 Archaeplastids include red algae, green
algae, and land plants
§ Archaeplastids include:
– red algae,
– green algae, and
– land plants.
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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.
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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.
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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.
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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.
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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.
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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.
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Other
consumers
Herbivorous
plankton
Carnivorous
plankton
Bacteria
Soluble
organic matter
Protistan
producers
secrete
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. Compare the characteristics of the three domains of life;
explain why biologists consider Archaea to be more closely
related to Eukarya than to Bacteria.
4. Describe the diverse types of Archaea living in extreme
and moderate environments.
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You should now be able to
5. Distinguish between the subgroups of the domain Bacteria,
noting the particular structure, special features, and
habitats of each group.
6.
Describe the steps of Koch’s postulates and explain why
they are used.
7.
Describe the extremely diverse assortment of eukaryotes.
8.
Explain how primary endosymbiosis and secondary
endosymbiosis led to further cellular diversity.
9.
Describe the major protist clades noting characteristics
and examples of each.
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You should now be able to
11. Explain how multicellular life may have evolved in
eukaryotes.
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