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Skills Worksheet
Active Reading
Section: Viruses
Read the passage below. Then answer the questions that follow.
Viruses are pathogens—agents that cause disease. Viruses lack
the enzymes necessary for metabolism and have no structures
to make proteins. Therefore, viruses must rely on living cells
for replication. Before a virus can replicate, it must first infect
a living cell.
In bacterial viruses, the cycle of viral infection, replication,
and cell destruction is called the lytic cycle. After the viral genes
have entered the cell, they use the host cell to replicate viral
genes and to make viral proteins, such as capsids. The proteins
are then assembled with the replicated viral genes to form complete viruses. The host cell is broken open and releases newly
made viruses.
During an infection, some viruses stay inside the cells but do
not make new viruses. Instead of producing virus particles, the
viral gene is inserted into the host chromosome and is called a
provirus. Whenever the cell divides, the provirus also divides,
resulting in two infected host cells. In this cycle, called the lysogenic cycle, the viral genome replicates without destroying the
host cell.
SKILL: READING EFFECTIVELY
Read each question, and write your answer in the space provided.
1. Why must viruses rely on living cells for replication?
2. What relationship exists between viruses and pathogens?
3. What sentence expresses the main idea of the second paragraph?
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Biology
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Viruses and Bacteria
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Active Reading continued
SKILL: INTERPRETING GRAPHICS
The figure below shows the lytic and lysogenic cycles. In the spaces provided,
describe what is occurring in each numbered part of the figure.
Lytic Cycle
Lysogenic Cycle
Part 1
Part 5
Part 2
Part 4
Part 3
4. Part 1: ______________________________________________________________
5. Part 2: ______________________________________________________________
6. Part 3: ______________________________________________________________
7. Part 4: ______________________________________________________________
8. Part 5: ______________________________________________________________
In the space provided, write the letter of the phrase that best completes the
statement.
______ 9. Viruses cause damage when they
a. invade cells.
b. replicate inside cells.
c. remain inside a host cell.
d. Both (a) and (b)
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Biology
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Viruses and Bacteria
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TEACHER RESOURCE PAGE
Answer Key
Directed Reading
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
SECTION: VIRUSES
1. Viruses do not grow, do not maintain
homeostasis, and do not metabolize.
2. They found that infected tobacco plant
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
sap from which bacteria had been
filtered still caused the disease.
Purified tobacco mosaic virus could
be crystallized, which is a property
of chemicals.
b
d
a
c
In the lytic cycle, the viral genes enter
the cell and use the host cell to replicate viral genes and to make viral
proteins, such as capsids. Complete
viruses are formed, and the cell is
broken open and destroyed, releasing
the viruses. In the lysogenic cycle,
the viral genome replicates without
destroying the host cell.
A provirus is the viral gene that has
been inserted into the host chromosome during the lysogenic cycle.
A pathogen is any agent that causes
disease.
HIV is the name of the virus that
causes AIDS. Individuals who have
AIDS are unable to defend themselves
against infections that do not normally
occur in healthy individuals.
Certain viruses can cause some types
of cancer. Viruses associated with
human cancers include hepatitis B
(liver cancer), Epstein-Barr virus
(Burkitt’s lymphoma), and human
papilloma virus (cervical cancer).
Both prions and viroids are infectious
agents. Prions consist of only proteins,
with no nucleic acids. Viroids consist
of only nucleic acid, with no proteins.
17.
18.
19.
20.
21.
22.
23.
Active Reading
SECTION: VIRUSES
1. Viruses do not have enzymes necessary
2.
3.
4.
5.
6.
7.
SECTION: BACTERIA
1.
2.
4.
5.
B
B
Gram-negative
bacteria and eukaryotes
pili and flagella
antibiotics
photosynthetic
photosynthetic
chemoautotrophic
heterotrophic
Bacteria compete for the proteins,
fats, carbohydrates, minerals, and
vitamins in your body.
Borrelia burgdorferi causes Lyme
disease. Lyme disease is transmitted
by the bite of an infected tick.
Dense collections of Streptococcus
mutans bacteria in the mouth cause
tooth decay.
Bacteria harm hosts by metabolizing
their hosts or by releasing toxins that
are poisonous to eukaryotic cells.
penicillin
viruses
Clostridium
oil
8.
9.
B
B
E
B
to support metabolism and have no
structures to make proteins.
Viruses are types of pathogens, or
agents that cause disease.
The cycle of viral infection, replication,
and cell destruction is called the lytic
cycle.
The virus attaches to a cell and injects
DNA.
Viral DNA enters the lytic cycle or
lysogenic cycle.
New viruses are made.
The cell breaks open and releases
viruses.
The provirus may enter the lytic cycle.
b
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Biology
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Viruses and Bacteria