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BIOLOGY 102 CHAPTER 16
Microbial Life: Prokaryotes and Protists
Learning Targets
Prokaryotes
16.1 Describe the diverse roles and abundance of prokaryotic life.
16.2 Compare the different shapes, cell walls, and projections of prokaryotes.
16.3 Explain how bacteria can evolve quickly and how bacteria can survive stressful environments.
16.4 Describe the nutritional diversity of prokaryotes.
16.5 Explain why biofilms are unique and potentially dangerous to human health.
16.6 Explain how prokaryotes are employed to address the needs of human society.
16.7 Compare the three domains of life based upon differences in cellular and biochemical traits. Exlain
why biologists consider Archaea to be more closely related to Eukarya than to Bacteria.
16.8 Describe the diverse types of Archaea living in extreme and more moderate
environments.
16.9 Distinguish between the subgroups of the domain Bacteria, noting the particular structure, special
features, and habitats of each group.
16.10 Describe some of the diseases associated with bacteria. Distinguish between exotoxins and endotoxins, noting examples of each.
16.11 Describe the four parts of Koch’s postulates. Explain why this method is used and how it relates to
our new understanding of the cause of most peptic ulcers.
16.12 Describe the recent U.S. attacks using bacteria and the effectiveness of anthrax as a weapon.
Protists
16.13 Describe the basic types of protists. Explain why biologists currently think that they represent many
clades.
16.14 Explain how primary endosymbiosis and secondary endosymbiosis led to further cellular diversity.
16.15 Describe and distinguish between the chromalveolate groups, noting characteristics and examples of
each.
16.16 Explain how cultured algae may be used as renewable fuels and the current challenges that remain.
16.17–16.20 Describe and distinguish between the Rhizaria, Excavata, Unikonta, and
Archaeplastida groups.
16.20 Describe the life cycle of Ulva, noting each form in the alternation of generations and how each is
produced.
16.21 Describe the protist ancestors of animals, plants, and fungi. Explain how each ancestral protist group
is similar to its most likely descendants.
Key Terms
alga (plural, algae)
Bacteria
ciliates
exotoxin
alternation of generabiofilm
coccus (plural, cocci)
extreme halophile
tions
bioremediation
cyanobacteria
extreme thermophile
amoebas
brown algae
diatoms
fimbriae
amoebozoan
cellular slime molds
dinoflagellates
foraminiferans
Archaea
chemoautotroph
endospore
gametophyte
autotroph
chemoheterotroph
endotoxin
Gram stain
bacillus (plural, bacilli)
chlamydias
Excavata
Gram-positive bacteria
mixotrophs
plasmodial slime mold
pseudopodium (plural,
green algae
parasite
plasmodium
pseudopodia)
heterotroph
pathogen
proteobacteria
radiolarians
kelp
peptidoglycan
protist
red algae
methanogens
photoautotroph
protozoan (plural, proRhizaria
photoheterotroph
tozoa)
secondary endosymbispirochetes
symbiosis
water molds
osis
sporophyte
Unikonta
Lecture Outline
I. Introduction
A. The abundant life of a coral reef depends upon microbes.
1. Photosynthesis by protists and prokaryotes feed all of the animals.
2. Prokaryotes convert dead organic material into fertilizer.
3. Protists that reside in the cells of corals use photosynthesis to produce sugars that nourish their
hosts.
B. Prokaryotes and protists are essential to the health of every ecosystem, including the
human body.
II. Prokaryotes
A. 16.1 Prokaryotes are diverse and widespread
1. Prokaryotic cells are smaller than eukaryotic cells.
a. Prokaryotes range from 1–5 µm in diameter.
b. Eukaryotes range from 10–100 µm in diameter.
2. The collective biomass of prokaryotes is at least 10 times that of all eukaryotes.
3. Prokaryotes live in habitats
a. too cold,
b. too hot,
c. too salty,
d. too acidic, and
e. too alkaline for eukaryotes to survive.
4. Some bacteria are pathogens, causing disease. But most bacteria on our bodies are benign or
beneficial.
5. Several hundred species of bacteria live in and on our bodies,
a. decomposing dead skin cells,
b. supplying essential vitamins, and
c. guarding against pathogenic organisms.
6. Prokaryotes in soil decompose dead organisms, sustaining chemical cycles.
B. 16.2 External features contribute to the success of prokaryotes
1. Prokaryotic cells have three common cell shapes.
a. Cocci are spherical prokaryotic cells. They sometimes occur in chains that are called streptococci.
b. Bacilli are rod-shaped prokaryotes. Bacilli may also be threadlike, or filamentous.
c. Spiral prokaryotes are like a corkscrew.
i. Short and rigid prokaryotes are called spirilla.
ii. Longer, more flexible cells are called spirochetes.
2. Nearly all prokaryotes have a cell wall. Cell walls
a. provide physical protection and
b. prevent the cell from bursting in a hypotonic environment.
3. When stained with Gram stain, cell walls of bacteria are either
a. Gram-positive, with simpler cell walls containing peptidoglycan, or
b. Gram-negative, with less peptidoglycan and are more complex and more likely to cause disease.
4. The cell wall of many prokaryotes is covered by a capsule, a sticky layer of polysaccharides or
protein.
5. The capsule
a. enables prokaryotes to adhere to their substrate or to other individuals in a colony and
b. shields pathogenic prokaryotes from attacks by a host’s immune system.
6. Some prokaryotes have external structures that extend beyond the cell wall.
a. Flagella help prokaryotes move in their environment.
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b. Hairlike projections called fimbriae enable prokaryotes to stick to their substrate or each
other.
C. 16.3 Populations of prokaryotes can adapt rapidly to changes in the environment
1. Prokaryote population growth
a. occurs by binary fission,
b. can rapidly produce a new generation within hours, and
c. can generate a great deal of genetic variation
i. by spontaneous mutations,
ii. increasing the likelihood that some members of the population will survive changes in the
environment.
2. The genome of a prokaryote typically
a. has about one-thousandth as much DNA as a eukaryotic genome and
b. is one long, circular chromosome packed into a distinct region of the cell.
3. Many prokaryotes also have additional small, circular DNA molecules called plasmids, which replicate independently of the chromosome.
4. Some prokaryotes form specialized cells called endospores that remain dormant through harsh
conditions.
5. Endospores can survive extreme heat or cold.
D. 16.4 Prokaryotes have unparalleled nutritional diversity
1. Prokaryotes exhibit much more nutritional diversity than eukaryotes.
2. Two sources of energy are used.
a. Phototrophs capture energy from sunlight.
b. Chemotrophs harness the energy stored in chemicals.
3. Two sources of carbon are used by prokaryotes.
a. Autotrophs obtain carbon atoms from carbon dioxide.
b. Heterotrophs obtain their carbon atoms from the organic compounds present in other organisms.
4. The terms that describe how prokaryotes obtain energy and carbon are combined to describe
their modes of nutrition.
a. Photoautotrophs obtain energy from sunlight and use carbon dioxide for carbon.
b. Photoheterotrophs obtain energy from sunlight but get their carbon atoms from organic
molecules.
c. Chemoautotrophs harvest energy from inorganic chemicals and use carbon dioxide for carbon.
d. Chemoheterotrophs acquire energy and carbon from organic molecules.
E. 16.5 CONNECTION: Biofilms are complex associations of microbes
1. Biofilms
a. are complex associations of one or several species of prokaryotes and
b. may also include protists and fungi.
2. Prokaryotes attach to surfaces and form biofilm communities that
a. are difficult to eradicate and
b. may cause medical and environmental problems.
3. Biofilms are large and complex “cities” of microbes that
a. communicate by chemical signals,
b. coordinate a division of labor and defense against invaders, and
c. use channels to distribute nutrients and collect wastes.
4. Biofilms that form in the environment can be difficult to eradicate.
5. Biofilms
a. clog and corrode pipes,
b. gum up filters and drains, and
c. Coat the hulls of ships.
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F. 16.6 CONNECTION: Prokaryotes help clean up the environment
1. Prokaryotes are useful for cleaning up contaminants in the environment because
prokaryotes
a. have great nutritional diversity,
b. are quickly adaptable, and
c. can form biofilms.
2. Bioremediation is the use of organisms to remove pollutants from
a. soil,
b. air, or
c. water.
3. Prokaryotic decomposers are the mainstays of sewage treatment facilities.
a. Raw sewage is first passed through a series of screens and shredders.
b. Solid matter then settles out from the liquid waste, forming sludge.
c. Sludge is gradually added to a culture of anaerobic prokaryotes, including bacteria and archaea.
d. The microbes decompose the organic matter into material that can be placed in a landfill or
used as fertilizer.
4. Liquid wastes are treated separately from the sludge.
a. Liquid wastes are sprayed onto a thick bed of rocks.
b. Biofilms of aerobic bacteria and fungi growing on the rocks remove much of the dissolved
organic material.
c. Fluid draining from the rocks is sterilized and then released, usually into a river or ocean.
5. Bioremediation is becoming an important tool for cleaning up toxic chemicals released into the
soil and water by industrial processes.
6. Environmental engineers change the natural environment to accelerate the activity of naturally
occurring prokaryotes capable of metabolizing pollutants.
G. 16.7 Bacteria and archaea are the two main branches of prokaryotic evolution
1. New studies of representative genomes of prokaryotes and eukaryotes strongly support the
three-domain view of life.
a. Prokaryotes are now classified into two domains:
i. Bacteria and
ii. Archaea.
b. Archaea have at least as much in common with eukaryotes as they do with bacteria.
H. 16.8 Archaea thrive in extreme environments—and in other habitats
1. Archaeal inhabitants of extreme environments have unusual proteins and other
molecular adaptations that enable them to metabolize and reproduce effectively.
a. Extreme halophiles thrive in very salty places.
b. Extreme thermophiles thrive in
i. very hot water, such as geysers, and
ii. acid pools.
2. Methanogens
a. live in anaerobic environments,
b. give off methane as a waste product from
i. the digestive tracts of cattle and deer and
ii. decomposing materials in landfills.
I. 16.9 Bacteria include a diverse assemblage of prokaryotes.
1. The domain Bacteria is currently divided into five groups, based on comparisons of
genetic sequences.
a. Proteobacteria
i. are all gram negative,
ii. share a particular rRNA sequence, and
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iii. represent all four modes of nutrition.
iv. Thiomargarita namibiensis is a type of proteobacteria that
(I) is a giant among prokaryotes, typically ranging up to 100–300 microns in
diameter,
(II) uses H2S to generate organic molecules from CO2, and
(III) produces sulfur wastes.
v. Proteobacteria also include Rhizobium species that
(I) live symbiotically in root nodules of legumes and
(II) convert atmospheric nitrogen gas into a form usable by their legume host.
(III) Symbiosis is a close association between organisms of two or more
species.
(IV) Rhizobium is an endosymbiont, living within another species.
b. Gram-positive bacteria
i. rival proteobacteria in diversity and
ii. include the actinomycetes common in soil.
iii. Streptomyces is often cultured by pharmaceutical companies as a source of many antibiotics.
c. Cyanobacteria
i. Cyanobacteria are the only group of prokaryotes with plantlike, oxygen-generating photosynthesis.
ii. Some species, such as Anabaena, have specialized cells that fix nitrogen.
d. Chlamydias
i. Chlamydias live inside eukaryotic host cells.
ii. Chlamydia trachomatis
(I) is a common cause of blindness in developing countries and
(II) is the most common sexually transmitted disease in the United States.
e. Spirochetes are
i. helical bacteria and
ii. notorious pathogens, causing
(I) syphilis and
(II) Lyme disease.
J. 16.10 CONNECTION: Some bacteria cause disease
1. All organisms are almost constantly exposed to pathogenic bacteria.
2. Most bacteria that cause illness do so by producing a poison.
a. Exotoxins are proteins that bacterial cells secrete into their environment.
b. Endotoxins are components of the outer membrane of gram-negative bacteria.
K. 16.11 SCIENTIFIC DISCOVERY: Koch’s postulates are used to prove that a bacterium causes a disease
1. Koch’s postulates are four essential conditions used to establish that a certain bacterium is the
cause of a disease. They are
a. find the bacterium in every case of the disease,
b. isolate bacteria from a person who has the disease and grow it in pure culture,
c. show that the cultured bacteria cause the disease when transferred to a healthy subject, and
d. isolate the bacteria from the experimentally infected subject.
2. Koch’s postulates were used to demonstrate that the bacterium Helicobacter pylori is the cause
of most peptic ulcers.
3. The 2005 Nobel Prize in Medicine was awarded to Barry Marshall and Robin Warren for this discovery.
L. 16.12 CONNECTION: Bacteria can be used as biological weapons
1. Bacteria that cause anthrax and the plague can be used as biological weapons.
a. Bacillus anthracis killed five people in the United States in 2001.
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b. Yersinia pestis bacteria
i. are typically carried by rodents and transmitted by fleas, causing the plague and
ii. can cause a pneumonic form of plague if inhaled.
2. Clostridium botulinum produces the exotoxin botulinum, the deadliest poison on earth.
3. Botulinum blocks transmission of nerve signals and prevents muscle contraction.
III. Protists
A. 16.13 Protists are an extremely diverse assortment of eukaryotes
1. Protists
a. are a diverse collection of mostly unicellular eukaryotes,
b. may constitute multiple kingdoms within the Eukarya, and
c. refer to eukaryotes that are not:
i. plants,
ii. animals, or
ii. fungi.
2. Protists obtain their nutrition in many ways. Protists include
a. autotrophs, called algae, producing their food by photosynthesis,
b. heterotrophs, called protozoans, eating bacteria and other protists,
c. heterotrophs, called parasites, deriving their nutrition from a living host, and
d. mixotrophs, using photosynthesis and heterotrophy.
3. Protists are found in many habitats including
a. anywhere there is moisture and
b. the bodies of host organisms.
4. Recent molecular and cellular studies indicate that nutritional modes used to categorize protists
do not reflect natural clades.
5. Protist phylogeny remains unclear.
6. One hypothesis, used here, proposes five monophyletic supergroups.
B. 16.14 EVOLUTION CONNECTION: Secondary endosymbiosis is the key to much of protist diversity
1. The endosymbiont theory explains the origin of mitochondria and chloroplasts.
a. Eukaryotic cells evolved when prokaryotes established residence within other,
larger prokaryotes.
b. This theory is supported by present-day mitochondria and chloroplasts that
i. have structural and molecular similarities to prokaryotic cells and
ii. replicate and use their own DNA, separate from the nuclear DNA of the cell.
2. Secondary endosymbiosis is
a. the process in which an autotrophic eukaryotic protist became endosymbiotic in a heterotrophic eukaryotic protist and
b. key to protist diversity.
C. 16.15 Chromalveolates represent the range of protist diversity.
1. Chromalveolates include
a. diatoms, unicellular algae with a glass cell wall containing silica,
b. dinoflagellates, unicellular autotrophs, heterotrophs, and mixotrophs that are common
components of marine plankton,
c. brown algae, large, multicellular autotrophs,
d. water molds, unicellular heterotrophs,
e. ciliates, unicellular heterotrophs and mixotrophs that use cilia to move and feed, and
f. a group including parasites, such as Plasmodium, which causes malaria.
D. 16.16 CONNECTION: Can algae provide a renewable source of energy?
1. Fossil fuels
a. are the organic remains of organisms that lived hundreds of millions of years ago and
b. primarily consist of
i. diatoms and
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E.
F.
G.
H.
ii. primitive plants.
2. Lipid droplets in diatoms and other algae may serve as a renewable source of energy.
3. If unicellular algae could be grown on a large scale, this oil could be harvested and processed into biodiesel.
4. Numerous technical hurdles remain before industrial-scale production of biofuel from algae becomes a reality.
16.17 Rhizarians include a variety of amoebas
1. The two largest groups of Rhizaria are among the organisms referred to as amoebas.
2. Amoebas move and feed by means of pseudopodia, temporary extensions of the cell.
3. Foraminiferans
a. are found in the oceans and in fresh water,
b. have porous shells, called tests, composed of calcium carbonate, and
c. have pseudopodia that function in feeding and locomotion.
4. Radiolarians
a. are mostly marine and
b. produce a mineralized internal skeleton made of silica.
16.18 Some excavates have modified mitochondria
1. Excavata has recently been proposed as a clade on the basis of molecular and
morphological similarities.
2. The name refers to an “excavated” feeding groove possessed by some members of the group.
3. Excavates
a. have modified mitochondria that lack functional electron transport chains and
b. use anaerobic pathways such as glycolysis to extract energy.
4. Excavates include
a. heterotrophic termite endosymbionts,
b. autotrophic species,
c. mixotrophs such as Euglena,
d. the common waterborne parasite Giardia intestinalis,
e. the parasite Trichomonas vaginalis, which causes 5 million new infections each year of human
reproductive tracts, and
f. the parasite Trypanosoma, which causes sleeping sickness in humans.
16.19 Unikonts include protists that are closely related to fungi and animals
1. Unikonta is a controversial grouping joining
a. amoebozoans and
b. a group that includes animals and fungi, addressed at the end of this unit on
Protists.
2. Amoebozoans have lobe-shaped pseudopodia and include
a. many species of free-living amoebas,
b. some parasitic amoebas, and
c. slime molds.
3. Plasmodial slime molds
a. are common where there is moist, decaying organic matter and
b. consist of a single, multinucleate mass of cytoplasm undivided by plasma membranes, called
a plasmodium.
4. Cellular slime molds
a. are common on rotting logs and decaying organic matter and
b. usually exist as solitary amoeboid cells, but when food is scarce, amoeboid cells
i. swarm together, forming a slug-like aggregate that wanders around for a short time and
then
ii. Form a stock supporting an asexual reproductive structure that produces spores.
16.20 Archaeplastids include red algae, green algae, and land plants
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1. Archaeplastids include
a. red algae,
b. green algae, and
c. land plants.
2. Red algae
a. are mostly multicellular,
b. contribute to the structure of coral reefs, and
c. are commercially valuable.
3. Green algae may be unicellular, colonial, or multicellular.
a. Volvox is a colonial green algae, and
b. Chlamydomonas is a unicellular alga propelled by two flagella.
4. Ulva, or sea lettuce, is
a. a multicellular green alga with
b. a complex life cycle that includes an alternation of generations that consists of
i. a multicellular diploid (2n) form, the sporophyte, that alternates with
ii. a multicellular haploid (1n) form, the gametophyte.
I. 16.21 EVOLUTION CONNECTION: Multicellularity evolved several times in
eukaryotes
1. The origin of the eukaryotic cell led to an evolutionary radiation of new forms of life.
2. Unicellular protists are much more diverse in form than simpler prokaryotes.
3. Multicellular organisms (seaweeds, plants, animals, and most fungi) are fundamentally different
from unicellular organisms.
a. A multicellular organism has various specialized cells that perform different functions and are
interdependent.
b. All of life’s activities occur within a single cell in unicellular organisms.
4. Multicellular organisms have evolved from three different lineages:
a. brown algae evolved from chromalveolates,
b. fungi and animals evolved from unikonts, and
c. red algae and green algae evolved from achaeplastids.
5. One hypothesis states that two separate unikont lineages led to fungi and animals,
diverging more than 1 billion years ago.
6. A combination of morphological and molecular evidence suggests that choanoflagellates are
the closest living protist relative of animals.
Word Roots
auto- = self; -troph = food (autotroph: an organism that makes its own food)
chemo- = chemical; auto- = self; -troph = food (chemoautotroph: an organism that obtains both energy and
carbon from inorganic chemicals, making its own organic compounds from CO2 without using light
energy); hetero- = different (chemoheterotroph: an organism that obtains both
energy and carbon from organic molecules)
cyan- = dark blue (cyanobacteria: Photoautotrophic prokaryotes with plantlike, oxygen-generating photosynthesis. These bacteria are sometimes called blue-green algae.)
endo- = inner, within (endospore: a thick-coated protective cell produced within a bacterial cell that can become dormant to survive harsh environmental conditions; endotoxin: a poisonous component of
the outer membrane of gram-negative bacteria, released only when the bacteria die)
exo- = outside (exotoxin: a poisonous protein secreted by certain bacteria)
-gen = produce (methanogen: Archaea that produce methane as a metabolic waste product)
halo- = salt; -philos = loving (extreme halophile: a microorganism that lives in a highly saline
environment)
hetero- = different (chemoheterotroph: an organism that obtains both energy and carbon from
organic molecules)
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photo- = light; auto- = self; -troph = food, nourish (photoautotroph: an organism that obtains
energy from sunlight and carbon from CO2)
-phyte = plant (gametophyte: the multicellular haploid form in the life cycle of organisms undergoing alternation of generations)
pseudo- = false; -podium = foot (pseudopodium [plural, pseudopodia]: a temporary extension of an amoeboid cell that functions in moving and feeding)
sym- = with, together; -bios = life (symbiosis: a close association between organisms of two or more species)
thermo- = heat; -philos = loving (extreme thermophile: a microorganism that thrives in a hot
environment)
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