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Chapter 19 Bacteria and Viruses
Section 19–1 Bacteria
(pages 471–477)
TEKS FOCUS: 4D Role of bacteria in maintaining health; 8C Characteristics of kingdoms—
archaebacteria and eubacteria 11D Role of microorganisms in maintaining equilibrium
This section describes two groups of prokaryotes and explains how they
differ. It also explains what factors are used to identify prokaryotes.
Introduction
(page 471)
1. What are prokaryotes? They are single-celled organisms that lack a nucleus.
2. Is the following sentence true or false? Prokaryotes are much smaller than most
eukaryotic cells.
true
Classifying Prokaryotes
(pages 471–472)
3. What are the two different groups of prokaryotes?
a. Eubacteria
b. Archaebacteria
4. Which is the larger of the two kingdoms of prokaryotes? Eubacteria
5. Where do eubacteria live? They live almost everywhere—including in water, on land, and on
and within the human body .
6. What protects a prokaryotic cell from injury? The cell wall protects it.
7. Circle the letter of what is within the cell wall of a prokaryote.
a. another cell wall
c. archaebacteria
b. cell membrane
d. pili
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8. What is peptidoglycan? It is a carbohydrate in the cell walls of eubacteria.
9. Some eubacteria have a second
membrane
outside the cell membrane.
10. Circle the letter of each sentence that is true about archaebacteria.
a. Their membrane lipids are different from those of eubacteria.
b. They lack a cell wall.
c. They lack peptidoglycan.
d. They look very similar to eubacteria.
11. What is significant about the DNA sequences of key archaebacterial genes?
They are more like those of eukaryotes than those of eubacteria.
12. How are archaebacteria related to eukaryotes? Scientists reason that archaebacteria may
be the ancestors of eukaryotes.
Guided Reading and Study Workbook/Chapter 19
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13. What are methanogens, and where do they live? They are prokaryotes that produce
methane gas. They live in oxygen-free environments, such as thick mud and the digestive tracts of
animals.
Identifying Prokaryotes
(page 473)
14. Complete the illustration of a typical prokaryote by labeling the parts.
Cell
membrane
Cell wall
DNA
Flagellum
15. What are four characteristics used to identify prokaryotes?
a. Their shape
b. The chemical nature of their cell walls
c. The way they move
d. The way they obtain energy
16. What are each of the differently shaped prokaryotes called?
.
b. The spherical-shaped are called
cocci
c. The corkscrew shaped are called
spirilla
.
.
17. A method of telling two different types of eubacteria apart by using dyes is called
Gram staining
.
18. What colors are Gram-positive and Gram-negative bacteria under the microscope
when treated with Gram stain? Gram-positive bacteria appear violet, and Gram-negative
bacteria appear red.
19. What are flagella? They are whiplike structures used for movement.
20. Is the following sentence true or false? Some prokaryotes do not move at all.
true
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bacilli
a. The rod-shaped are called
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Metabolic Diversity
Class __________________
Date ______________
(pages 473–474)
21. Complete the table about prokaryotes classified by the way they obtain energy.
GROUPS OF PROKARYOTES
Group
Description
Photoautotroph
Organism that carries out photosynthesis in a manner similar to plants
Chemoautotroph
Organism that obtains energy directly from chemical reactions involving
inorganic molecules
Heterotroph
Organism that takes in organic molecules and then breaks them down
Photoheterotroph
Organism that captures sunlight for energy and also needs organic molecules
as a carbon source
22. Members of which group of photoautotrophs contain a bluish pigment and
Cyanobacteria
chlorophyll a?
23. How do the chemoautotrophs that live near hydrothermal vents on the ocean floor
obtain energy? They obtain energy from hydrogen sulfide gas that flows from the vents.
24. Complete the table about prokaryotes classified by the way they release energy.
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GROUPS OF PROKARYOTES
Group
Description
Obligate aerobes
Organisms that require a constant supply of oxygen
Obligate anaerobes
Organisms that must live in the absence of oxygen
Facultative anaerobes
Organisms that can survive with or without oxygen
25. Facultative anaerobes can switch between cellular respiration and
Growth and Reproduction
fermentation
.
(page 475)
26. What occurs in the process of binary fission? It is a type of asexual reproduction in which a
prokaryote grows to nearly double its size, replicates its DNA, and divides in half, producing two
identical “daughter” cells.
27. What occurs during conjugation? A hollow bridge forms between two cells, and genes move
from one cell to the other.
28. Is the following sentence true or false? Most prokaryotes reproduce by conjugation.
false
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29. What is an endospore? It is a type of spore that is formed when a bacterium produces a thick
internal wall that encloses its DNA and a portion of its cytoplasm.
Importance of Bacteria
(pages 476–477)
30. How do decomposers help the ecosystem recycle nutrients when a tree dies?
Armies of bacteria attack and digest the dead tissue. The bacteria break down dead matter into
simpler materials, which are released into the soil.
31. What would happen to plants and animals if decomposers did not recycle nutrients?
Plants would drain the soil of minerals and die, and animals that depend on plants for food would
starve.
32. Why do plants and animals need nitrogen? They need nitrogen to make amino acids,
which are the building blocks of proteins.
33. How does nitrogen fixation help plants? Plants use the nitrogen to build amino acids.
34. What kind of relationship do many plants have with nitrogen-fixing bacteria?
They have symbiotic relationships.
35. How can bacteria be used to clean up an oil spill? One type of bacterium can digest
petroleum.
36. What have biotechnology companies begun to realize about bacteria adapted
to extreme environments? Those bacteria may be a rich source of heat-stable enzymes,
which can be used in medicine, food production, and industrial chemistry.
Writing a summary can help you remember the information you have read. When
you write a summary, write only the most important points. Write a summary of the
information under the green heading Decomposers. Your summary should be shorter
than the text on which it is based. Do your work on a separate sheet of paper.
Students’ summaries should include the main points about how some bacteria are critical in recycling
nutrients in the environment.
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Reading Skill Practice
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Section 19–2 Viruses
Class __________________
Date ______________
(pages 478–483)
TEKS FOCUS: 3F Contributions of scientists in biology; 4C Compare viruses to cells
This section describes the structure of a virus. It also explains how viruses
cause infection.
What Is a Virus?
(pages 478–479)
1. What are viruses? They are particles of nucleic acid, protein, and in some cases lipids that can
reproduce only by infecting living cells.
2. What do all viruses have in common? They enter living cells and, once inside, use the
machinery of the infected cell to produce more viruses.
3. Is the following sentence true or false? Most viruses are so small that they can be seen
only with the aid of a powerful electron microscope.
true
4. What is the structure of a typical virus? A typical virus is composed of a core of either DNA
or RNA surrounded by a protein coat.
5. Circle the letter of what a virus’s protein coat is called.
a. capsid
b. envelope
c. head
d. lysis
6. How does a typical virus get inside a cell? The capsid proteins bind to receptors on the
surface of a cell and “trick” the cell into allowing it inside.
7. What occurs when viruses get inside of cells? Once inside, the viral genes are expressed.
The cell transcribes and translates the viral genetic information into viral capsid proteins. Sometimes
the program may cause the cell to make copies of the virus, and in the process the host cell
is destroyed.
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8. Why are most viruses highly specific to the cells they infect? Viruses must bind precisely
to proteins on the cell surface and then use a host’s genetic system.
9. What are bacteriophages? They are viruses that infect bacteria.
Viral Infection
(pages 480–481)
10. Why is a lytic infection given that name? The host cell is lysed and destroyed.
11. Circle the letter of each sentence that is true about a lysogenic infection.
a. The virus lyses the host cell immediately.
b. The virus embeds its DNA into the host’s DNA.
c. The virus’s DNA is replicated along with the host cell’s DNA.
d. A host cell makes copies of the virus indefinitely.
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12. Complete the flowchart about a lytic infection.
cell wall
The bacteriophage attaches to the bacterium’s
DNA
The bacteriophage injects its
.
into the cell.
genes
The cell makes mRNA from the bacteriophage’s
burst
The virus wrecks the cell, causing it to
The bursting of the cell releases new bacteriophage
.
.
particles
.
13. What is a prophage? It is the viral DNA that is embedded in the host’s DNA.
Retroviruses
(page 482)
14. What are retroviruses? They are viruses that contain RNA as their genetic information.
15. What happens when retroviruses infect a cell? They produce a DNA copy of their RNA.
This DNA is inserted into the DNA of the host cell.
(pages 482–483)
16. Circle the letter of each reason why some biologists do not consider viruses to be alive.
a. They can’t infect living cells.
b. They can’t evolve.
c. They can’t regulate gene expression.
d. They can’t reproduce independently.
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Viruses and Living Cells
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Section 19-3 Diseases Caused by Bacteria and Viruses
(pages 485-490)
TEKS FOCUS: 4C Role of viruses in causing disease; 4D Role of bacteria in causing disease;
11D Role of microorganisms in maintaining equilibrium
This section describes bacterial and viral diseases.
Bacterial Disease in Humans
(pages 485–486)
They
are
disease-causing
agents.
1. What are pathogens?
2. What are the two general ways that bacteria cause disease?
a. Some damage the tissues of the infected organism directly by breaking them down for food.
b. Others release toxins that harm the body.
3. What kind of tissue do the bacteria that cause tuberculosis break down?
They break down lung tissue.
4. What are antibiotics? They are compounds that block the growth and reproduction of bacteria.
5. What is one of the major reasons for the dramatic increase in life expectancy during the
past two centuries? There is an increased understanding of how to prevent and cure bacterial
infections.
Controlling Bacteria
(pages 487–488)
6. What is sterilization? It is a way of destroying all bacteria by subjecting them to great heat.
disinfectant
7. A chemical solution that kills pathogenic bacteria is called a(an)
.
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8. Why will food stored at low temperatures keep longer? The bacteria in the food will take
much longer to multiply.
9. How can food be preserved through canning? This method involves heating food to a high
temperature and then immediately placing it into sterile glass jars or metal cans and sealing the
container.
10. What everyday chemicals can be used to inhibit the growth of bacteria in food?
They include salt, vinegar, and sugar.
Viral Disease in Humans
(pages 488–489)
11. What are some human diseases that viruses cause? Viruses cause polio, measles, AIDS,
mumps, influenza, yellow fever, smallpox, the common cold, and many other diseases.
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Viral Disease in Animals
Class __________________
(page 488)
oncogenic viruses
12. Cancer-causing viruses are known as
Viroids and Prions
Date ______________
.
(page 490)
13. A disease-causing particle that contains only protein and not DNA or RNA is called
prion
a(an)
.
WordWise
Answer the questions by writing the correct vocabulary terms in the blanks.
Use the circled letter in each word to find the hidden word. Then, write a
definition for the hidden word.
What is the viral DNA that is embedded in a host’s DNA?
p
r
o
p
h
a
g
e
What is a rod-shaped bacterium?
b
a
c
i
l
l
u
s
What is a compound that blocks the growth and reproduction of bacteria?
a
n
t
i
b
i
o
t
i
c
p
h
What is a virus that infects bacteria?
b
a
c
t
e
r
i
o
a
g
e
What is a prokaryote that can capture sunlight for energy but also needs organic
compounds for nutrition?
p
h
o
t
o
h
e
t
e
r
o
t
r
o
p
h
What is the exchange of genetic information that occurs from one bacterium to another
through a hollow bridge?
o
n
j
u
g
a
t
i
o
n
What is a virus that contains RNA as its genetic information?
r
e
t
r
o
v
i
r
u
s
What is the process in which nitrogen is converted into a form plants can use?
n
i
t
r
Hidden Word: p
o
g
a
e
t
n
h
f
o
g
i
e
x
a
t
i
o
n
n
Definition: A disease-causing agent
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c