Download chapter 34: bacteria

CHAPTER 28: PROKARYOTES
WHERE DOES IT ALL FIT IN?
Chapter 28 follows the approach of Chapter 27 and highlights the diversity of prokaryotes. Students
should be encouraged to recall the principles of prokaryotic cell structure and evolution associated
with the particular features of prokaryotic cells. The information in chapter 28 does not stand alone.
Students should know that bacteria and other organisms are interrelated and originated from a
common ancestor of all living creatures on Earth.
SYNOPSIS
Prokaryotic organisms represent the oldest forms of life. Prokaryotic organisms are extremely
adaptable to changing environments, found in a variety of land and aquatic habitats, involved in
photosynthesis, decomposition and nitrogen fixation processes, commercially important in the
production of food and chemicals and have applications in genetic engineering
Prokaryotic organisms differ from eukaryotic organisms in the following way: unicellular, cell
size, chromosomes organization, cell division and genetic recombination, internal
compartmentalization, flagella structure, and metabolic diversity. Bacteria are single-celled
organisms, but can exist singularly, in colonies or in filamentous organizations. There are few
integrated activities between prokaryotic cells and no true specialization of cells as found in even
the most primitive multicellular organisms. Bacteria do not possess chromosomes like
eukaryotes as their genes are contained in a single, double-stranded ring of DNA found in the
nucleoid region of the cell. They lack internal compartmentalization and do not have any
membrane-bound organelles. Internally, they have a complex membrane system formed from
invaginations of the plasma membrane. Photosynthetic and/or respiratory enzymes may be
associated with these membranes. Like eukaryotes, they have ribosomes, but they are distinctly
different in protein and RNA content.
Prokaryotic organisms are divided into two major groups: the archaebacteria (or Archaea) and
bacteria. Archaebacteria are distinctly different from the bacteria. They have a unique cell wall
composition and different kinds of lipids in their membranes. Their gene translation machinery is
more like that of eukaryotes than the bacteria and they have some genes with introns, something
completely lacking in bacteria. Early classification schemes used form, habitat, and differential
stains in classifying prokaryotic organisms, particularly the bacteria. Two major types of
bacteria can be classified as being Gram negative (red stain) or Gram positive (purple stain)
based on their outer membrane construction. Morphologically, most bacteria appear either
spherical (cocci), rod-shaped (bacilli), or spirally coiled (spirilla). As there are few structural
differences among bacteria groups, they therefore are further classified by their metabolic
processes. Photoautrotrophs carry out photosynthesis in sunlight and build organic molecules
from carbon dioxide. Chemoautrophs oxidize inorganic compounds, including ammonia,
nitrates, sulfur, and hydrogen gas. Photoheterotrophs, exemplified by the purple nonsulfur
bacteria, use light but obtain their carbon from carbohydrates or alcohols. Chemoheterotrophs
obtain both carbon and energy from organic molecules and include decomposers and pathogenic
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bacteria. In addition, each species of bacteria utilizes the components of specially defined media
on which it is grown in a certain characteristic manner. They may utilize only certain
carbohydrates or other carbon sources, produce various fermentative gases and pigments, or
produce pH changes.
Bacteria structure, although simple, is no less complex compared to eukaryotic organisms.
Bacteria cell walls are composed of peptidoglycan. They may possess rigid, helical flagella, or
hair-like pili. Some bacteria form thick-walled endospores that are extremely resistant to heat.
Internal structures include: internal membranes for photosynthesis or respiration, a nucleoid
region that contains the single double-stranded DNA ring, and ribosomes involved in protein
synthesis. Genetic variation in bacteria results from exchange of DNA fragments or by mutation.
A high rate of mutation coupled with a very short generation time can rapidly change the
characteristics of a bacterial population.
Bacteria are serious plant and human pathogens. Most plant pathogens are rod-shaped
pseudomonads, while animal pathogens are extremely diverse. In addition, bacteria cause a wide
variety of human diseases including anthrax, botulism, Chlamydia, cholera, dental caries,
diphtheria, gonorrhea, leprosy, lyme disease, peptic ulcers, plague, pneumonia, tuberculosis,
typhoid fever, and typhus. Tuberculosis has been around for thousands of years with millions of
new cases reported worldwide each year. Dental caries are caused by a wide variety of bacteria,
exacerbated by high sugar diets. The many sexually transmitted diseases (STDs) are causing
widespread problems throughout society with many becoming resistant to antibiotic treatment.
Bacteria are important in the cycling of chemical elements within our ecosystem. As
decomposers, they can release previously locked up elements back into the environment.
Bacteria are also important in fixation in which they return elements from the environment to
organisms. Bacteria have been used to produce food products such as beer, wine, yogurt, and
cheeses. They are biofactories used to produce enzymes, vitamins, and antibiotics. Many
bacteria live in association with other organisms. A commensal relationship is one in which the
bacteria benefits, while the other animal/plant is neither benefited nor harmed. A parasitic
relationship is one in which the bacterium benefits and the other organism is harmed. Genetic
engineering methods have been applied to bacteria to produce improved strains of bacteria for
commercial purposes such as producing therapeutic proteins, removing pollutants from the
environment, and controlling pest outbreaks.
For decades, many countries have been involved in a bioweapons programs. Pathogenic bacteria
pose immediate threats in bioterrorism attacks.
LEARNING OUTCOMES
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Differentiate and compare prokaryotes versus eukaryotes.
Differentiate and compare archaebacteria with bacteria.
Know the features and functions of structures found in bacteria.
Understand why mutation is important to the genetic diversity of bacteria.
Differentiate among photosynthetic, chemoautotrophic, and heterotrophic bacteria in terms of
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how they obtain energy.
Illustrate the importance of bacteria as pathogens.
Illustrate the importance of the benefits of bacteria in the ecosystem, genetic engineering and as
biofactories.
Discuss the role of bacteria in biterrorism.
COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information
will inhibit the learning of concepts related to the misinformation. The following concepts
covered in Chapter 28 are commonly the subject of student misconceptions. This information on
“bioliteracy” was collected from faculty and the science education literature.
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Students believe that prokaryotes have DNA within a nucleus
Students believe that prokaryotes have organelles
Students believe that all bacteria cause disease
Students believe that prokaryotes only thrive at the same environmental conditions as
humans
Students believe that prokaryotic DNA does not differ from eukaryotic DNA
Students believe that prokaryotic DNA lacks introns
Students believe that prokaryotes evolved from viruses
Students believe that all bacteria have cell walls
Students believe that bacterial cell walls are made of cellulose
Student believe that genetically modified bacteria are inherently dangerous
Students believe that species are genetically distinct and fixed
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
Be certain to stress that prokaryotic organisms are now divided up into two groups: Archaea and
bacteria. (Note: eubacteria are referred to as bacteria.) Identify the differences between Archaea
and bacteria. Then discuss the differences between the bacteria groups. Stress that although the
initial classification of bacteria was related to structure (shape, flagella, morphology, Gram
reaction, endospores), today’s classification is based on metabolic differences. It is difficult to
maintain bacteria so that they exhibit their characteristic metabolic traits since they mutate so
readily. The American Type Culture Collection (ATCC) characterizes bacteria to ensure their
proper metabolic identity for biological research. One can periodically compare the biochemical
tests of a laboratory strain against the ATCC standard.
Bacterial pathogens are a serious threat to the food industry. Detection of contaminants requires
time-consuming culturing to detect relatively large quantities of bacteria. Frequently
contamination is only recognized after people become sick or die. Water is checked for sewage
contamination by determining the presence of nonpathogenic bacteria that are present in greater
numbers than the harmful forms. Recent advances in molecular technology and monoclonal
antibodies provide much faster identification of such pathogens. These tests also detect much
smaller quantities of harmful bacteria.
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Legumes (peas, clover) possess root nodules containing Rhizobium bacteria that fix nitrogen.
These nodules contain a protein called leghemoglobin that is produced by the plant. It is
structurally related to animal hemoglobin and is also red in color. It binds free oxygen in the
nodule, enabling the obligate anaerobe to reproduce and metabolize.
Researchers at the University of Georgia have developed a cheap and effective way to kill
bacteria on food and utensils—electrolyzed water. The water is prepared by running an electrical
current through a dilute saltwater solution. The antimicrobial effect may be a result of the
chlorine that is produced. The water is also highly acidic and contains substantially less oxygen
than normal water.
Iceminus pseudomonas has been genetically engineered to prevent frost formation in the citrus
industry. Other pseudomonads have caused problems in the hot tub industry as they thrive in
warm water that may not be sufficiently chlorinated. Still others cause havoc with the
refrigeration of meat and dairy products as they continue to multiply in large numbers in cool,
refrigerated environments.
Many companies are taking advantage of the public’s fear of microorganisms causing health
problems. Under normal household circumstances there is absolutely no need to use antibacterial
soaps! Soap and hot water are sufficient to deal with the kinds of bacteria present in homes.
Overuse of such antibacterial products may result in the same kind of resistance now experienced
with antibiotics taken to combat disease.
HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the
lecture and the textbook. A complete understanding of biology content provides students with the
tools to synthesize new hypotheses and knowledge using the facts they have learned. The
following table provides examples of assessing a student’s ability to apply, analyze, synthesize,
and evaluate information from Chapter 28.
Application
Analysis
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Have students explain if antibiotics that prevent cell wall formation would
be effective against all bacteria.
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Have students describe relative survivability of spore forming bacteria
and non-spore forming bacteria after washing hands with antibacterial
soaps.
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Ask students to explain if vacuum sealing of foods is effective to reduce
the growth of bacteria during storage.
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Have students compare and contrast viruses and bacteria.
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Ask students distinguish between the needs of photoautotrophs and
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photochemotrophs
Synthesis
Evaluation
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Ask students to explain the pros and cons of using genetically bacteria to
produce commercially important proteins.
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Ask students explain the implications of producing nitrogen fixing
capable of entering the roots of any crop plant.
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Have the students hypothesize some feasible and realistic ways of using
bacteria to produce energy
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Ask the students hypothesize about genetically modified bacteria that can
be used to reduce household waste.
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Ask students evaluate the pros and cons giving a person an antibiotic that
kills all bacteria on the body.
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Ask students to evaluate the relative safety and effectiveness of using
bacterial proteins instead of chemicals such as glycol as antifreeze on
airplane wings.
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Ask students to evaluate the issues of placing harmless bacteria on foods
on a way of preventing the growth of disease–causing bacteria.
VISUAL RESOURCES
Electron micrographs of bacteria are much more impressive than light micrographs. In addition,
bring in samples of live bacteria in Petri dishes. There are a wide variety of colorful organisms
available. Many biological supply companies sell already prepared plates; others sell “instant”
media in the form of culture impregnated cellulose pads or a gel that is activated simply by
adding sterile water. If you have your students prepare random inoculations by exposure to the
air, coughing on plates, and so forth, make sure the plates stay sealed for safety! As an example,
collect various soil samples and dilute them with water. Using a sterile Q-tip, dip it in the
soil/water sample, and inoculate the Petri dish. Put it in a warm environment, and in about a day,
you’ll see many types of bacteria colonies.
IN-CLASS CONCEPTUAL DEMONSTRATIONS
A. Building a Prokaryote
Introduction
Student directed modeling is a fun and effective way to review the structural and
chemical characteristics of organisms. This quick activity has students review the structure and
metabolism of different prokaryotes.
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Materials
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Cell Structure
o Modeling clay
o Toothpicks
o Large self-sealing plastic bag
o Cardboard box large enough to hold the self-sealing bag filled with water
o Aluminum foil
o Water
o Plastic wrist band
o Large plastic beads or buttons
o Tennis ball
Metabolism
o Lamp or light bulb
o Bottle of household ammonia
o Large rock
o Dead plant
o Stuffed animal
o Small vacuum cleaner
Procedure & Inquiry
1. Tell students that you want to have the class review the characteristics of prokaryotes.
2. Review shape and colony size by rolling the clay into shapes resembling cocci, bacilli,
spirilla. Have the students name the shape.
3. Then use the toothpicks to for the cocci or bacilli into various colonies. Have the students
name the colony shape.
4. They use the following materials to “build” a typical prokaryote:
a. Cell membrane - self-sealing plastic bag
b. Cell wall – cardboard box
c. Slime layer or capsule - aluminum foil
d. Cytoplasm - water
e. DNA - plastic wrist band
f. Ribosome - plastic beads or buttons
g. Endospore - tennis ball
5. Have the students name what is needed for the cell.
6. Build the cell in cooperation with the student comments.
7. Ask the students about the nature of the structures including the cell wall and its Gram
staining features
8. Then use the metabolism props to review the types of bacterial feeding characteristics:
a. Photoautotrophs and photoheterotrophs - Lamp or light bulb
b. Chemoautotrophs - bottle of household ammonia
c. Chemoautotrophs - large rock
d. Chemoheterotrophs (decomposers) - dead plant
e. Chemoheterotrophs (parasites or pathogens) - stuffed animal
f. Anaerobes – small vacuum cleaner
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9. Summarize the events with the class when the demonstration is completed.
USEFUL INTERNET RESOURCES
1. Images of bacteria and microbiological techniques are available from the American
Society of Microbiology. These images are valuable teaching resources for lecture and
laboratory sessions. The site is available at
http://www.microbelibrary.org/about/index.asp?bid=1088.
2. The Karolinska Institutet University Library in Stockholm, Sweden hosts useful weblink
page for accurate and contemporary information about bacterial diseases. It is a good
source of information about emergent diseases. This website located at
http://www.mic.ki.se/Diseases/C01.html.
3. The Tree of Life website provides up to date information about archaea and prokaryote
classification. It has useful information and images for showing students diversity of
prokaryotes. The website can be found at http://www.tolweb.org/Life_on_Earth/1.
4. Cases studies are an effective tool for reinforcing a lecture on the nature of bacterial
diseases. The University of Buffalo provides a teaching case study called “Dr. Collins
and the Case of the Mysterious Infection”. It has students investigate issues related to
identifying bacterial diseases. The case study can be found at
http://www.sciencecases.org/infection/infection.pdf.
LABORATORY IDEAS
This activity provides some interesting insight into the prevalence of bacteria on
everyday items such as paper currency. Students are asked to hypothesize about their findings
from culturing bacteria from dollars.
a. Tell students that they will be investigating the feasibility of obtaining bacterial infections
by handling money.
b. Provide students with the following materials
a. Nutrient agar plates
b. Blood agar plates
c. Sterile swabs
d. Antibiotic discs
i. Penicillin
ii. Tetracycline
iii. Vancomycin
c. Instruct students to design an experiment to test the potential for money to spread
bacterial infections.
d. Instruct them how to make swab plates on the nutrient agar and blood agar media.
e. Have the collect bacteria from paper money, coins, or even credit cards that they carry
with them.
f. Also ask them to determine if it is possible that these bacteria are insensitive to antibiotic
treatments.
g. Have the students research the different antibiotics and antibiotic resistance.
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LEARNING THROUGH SERVICE
Service learning is a strategy of teaching, learning and reflective assessment that merges the
academic curriculum with meaningful community service. As a teaching methodology, it falls
under the category of experiential education. It is a way students can carry out volunteer projects
in the community for public agencies, nonprofit agencies, civic groups, charitable organizations,
and governmental organizations. It encourages critical thinking and reinforces many of the
concepts learned in a course.
1. Have students do a lesson do a demonstration to elementary school students on things to
do to prevent the spread of bacterial diseases.
2. Have students work with an STD education center.
3. Have students produce literature on bacterial diseases for a local health fair.
4. Have students produce a meningitis display at a local high school or library.
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