Name: ______________________________________
Date: ________________________
Student Exploration: Virus Lytic Cycle
Vocabulary: bacteriophage, capsid, host cell, lyse, lytic cycle, virus
Log on to www.explorelearning.com and launch the gizmo: Virus Lytic Cycle
Imagine a sinister (and, luckily, fictional) military tank driving around in Toronto,
where many Canadian cars are made. Imagine that the tank finds a major auto factory
and crashes through the wall into the plant, destroying itself.
Imagine then that the crew (also sinister) gets out from the wrecked tank and retrains the factory's workers to make other sinister tanks. The plant produces more and
more tanks until soon the factory can hold no more, and it literally bursts. Hundreds of
tanks crash through the walls in every direction and rumble off across the countryside in
search of more auto factories, where the process is repeated.
This story, while strange, is a remarkably accurate analogy of the life cycle of a
virus. That tank represents a virus and the automotive factory is an infected cell. In the
vocabulary of viruses, you can say that the virus causes the infected cell to burst, or
lyse. A virus that causes this is called a lytic virus.
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. A computer virus is a program that can copy itself and infect a computer without the
permission of the owner. How do you think a computer virus compares to a real virus?
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2. Have you ever been infected with a virus, such as the cold virus or flu virus? ____________
3. If so, how did the virus affect you? _____________________________________________
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Gizmo Warm-up
A virus is a microscopic particle that can infect a cell.
Viruses are primarily composed of a protein coat,
called a capsid, and nucleic acid. In the Virus Lytic
Cycle Gizmo™, you will learn how a virus infects a
cell and uses the cell to produce more viruses.
1. Viruses are extremely small. A typical virus is
about 100 times smaller than a single cell, such
as a bacterium. Label the virus and a bacterial
cell in the image at right.
2. Bacteriophages are
viruses that infect
bacteria. Based on the
diagram at left, label
the head, tail, tail fibers,
and the strand of
nucleic acid in the
image at right.
COMPLETE THIS QUIZ AFTER THE GIZMO
Assessment Questions (5):
1. How many cells have been killed by the virus in the image here?
A. 7
B. 13
C. 20
D. 29
2. Which of the following is NOT a component of a virus?
A. plasma membrane
B. protein capsid
C. nucleic acid
D. tail section
3. What component of a virus is injected into the infected cell?
A. the tail section
B. the nucleic acid
C. the protein capsid
D. the mitochondria
4. How does a lytic virus kill the cells that it infects?
A. It stops energy production by the cell's mitochondria.
B. It allows the cell's cytoplasm to enter the nucleus, which destroys the cell's DNA.
C. It causes the cell membrane to rupture.
D. It destroys chlorophyll molecules so that the cell cannot conduct photosynthesis.
5. Suppose that one virus infects one cell, and 300 minutes later 100 cells are dead (experienced lysis)
due to viruses. Which of the following is most likely to describe when lysis occurred for those 100
cells?
A. Lysis occurred for zero cells in the first 150 minutes and for all 100 cells in the last 150 minutes.
B. Lysis occurred for 30 cells in the first 150 minutes and for 70 cells in the last 150 minutes.
C. Lysis occurred for 50 cells in the first 150 minutes and for 50 cells in the last 150 minutes.
D. Lysis occurred for 70 cells in the first 150 minutes and for 30 cells in the last 150 minutes.
Activity A:
Lytic cycle
Get the Gizmo ready:
 If necessary, click Reset (
).
Introduction: Unlike living organisms, viruses cannot reproduce on their own. Instead, viruses
infect host cells, taking over the cell’s machinery to produce more viruses. This process is
called the lytic cycle.
Question: What are the steps of the lytic cycle?
1. Observe: Use the navigation arrows on the DESCRIPTION tab to read about the stages of
the lytic cycle. Using your own words, summarize each step of the cycle.
Step
Summary
1
↓
2
↓
3
↓
4
↓
5
(Activity A continued on next page)
Activity A (continued from previous page)
2. Analyze: The yellow ring inside the bacterial cell represents the bacterial DNA. Why does
this structure disappear by step 3 of the lytic cycle?
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3. Describe: How does a virus destroy the host cell’s DNA? ____________________________
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4. Describe: How are new viruses reproduced? _____________________________________
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5. Think and discuss: Why can’t a virus reproduce on its own? _________________________
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6. Justify: To lyse is to burst apart or explode. Why do you think a virus’s reproduction cycle is
called the “lytic cycle”?
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Activity B:
Get the Gizmo ready:
Spread of
infection
 If necessary, click Reset.
Question: How does a viral infection spread?
1. Predict: Suppose that a virus infects a small population of bacteria. Predict how the numbers
of viruses, infected cells, and uninfected cells will change as the infection progresses. On
the blanks below, write increase, decrease, or stay the same.
Viruses: _______________________
Infected cells: _______________________
Uninfected cells: _______________________
2. Observe: Click Play (
), and watch the simulation. Describe what you see.
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3. Test: Click Reset, and Select the BAR CHART tab. Turn on Show numerical values. Click
Play, and watch each bar as the simulation runs. What do you notice, and how does this
compare to your predictions?
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4. Record data: Select the TABLE tab, and use the data to complete the second column of the
table below. To complete each cell in the third column, subtract the previous time value from
the current time value. For example, if it took 80 minutes to reach 40 cells and 100 minutes
to reach 30 cells, then the time difference is 20 minutes.
Number of cells
Time (m)
Amount of time to decrease
population by 10
50
0m
--
40
30
20
10
(Activity B continued on next page)
Activity B (continued from previous page)
7. Analyze: What trend do you see in the third column of your data table? ________________
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8. Explain: How would you explain this trend? ______________________________________
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9. Interpret: Select the GRAPH tab. Run the Gizmo again, and observe what happens in the
SIMULATION pane when the graph shows a decrease in the viruses’ population size.
A. Why does the number of viruses sometimes increase and sometimes decrease?
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B. Sometimes when a virus enters a cell, it becomes dormant for a while. Why might
this make it difficult for a doctor to diagnose a viral infection?
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10. Extend your thinking: AIDS is one disease
caused by a virus infection. The virus attacks
immune system cells known as T cells.
Based on your observations from the Gizmo,
how would you explain the data shown on
this graph?
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