Viruses

1
Table of Contents

• Viruses
• Bacteria
• Viruses, Bacteria, and Your Health

2
What Is a Virus?
- Viruses

• A virus is a tiny nonliving particle that enters
  and then reproduces inside a living cell. Virus
  particles are tiny compared to bacteria.

3
The Structure of Viruses
- Viruses
4
How Viruses Multiply
- Viruses

• Active viruses enter cells and immediately begin
  to multiply, leading to the quick death of the
  invaded cells.

5
Diameter
- Viruses

• The diameter of a circle is a line that passes
  through the center of the circle and has both of
  its endpoints on the circle. To find the
  diameter, draw a line like the one shown below.
  Then use a metric ruler to measure the length of
  the line. For example, the diameter of a penny is
  about 1.9 mm.

6
Diameter
- Viruses

• Practice Problem
• Measure the diameter
• of a quarter.

• 2.4 cm

7
Diameter
- Viruses

• Practice Problem
• Measure the diameter
• of a CD.

• 12 cm

8
How Viruses Multiply
- Viruses

• Hidden viruses hide for a while inside host
  cells before becoming active.

9
Active and Hidden Viruses Activity
- Viruses

• Click the Active Art button to open a browser
  window and access Active Art about active and
  hidden viruses.

10
Sequencing
- Viruses

• As you read, make two flowcharts that show how
  active and hidden viruses multiply. Put the steps
  in the process in separate boxes in the
  flowchart, in the order in which they occur.

How Active Viruses Multiply
Virus attaches to the surface of a living cell.
Virus injects genetic material into cell.
Cell produces viral proteins and genetic material.
Viruses assemble.
Cell bursts, releasing viruses.
11
Sequencing
- Viruses

• As you read, make two flowcharts that show how
  active and hidden viruses multiply. Put the steps
  in the process in separate boxes in the
  flowchart, in the order in which they occur.

How Hidden Viruses Multiply
Virus attaches to cell.
Virus injects its genetic material.
Viruss genetic material becomes part of cells
genetic material.
Cell produces viral proteins and genetic material.
Viruses are assembled.
Cell bursts, releasing viruses.
12
Deadly Virus
- Viruses

• Click the Video button to watch a movieabout
  deadly viruses.

13
End of SectionViruses
14
The Bacterial Cell
- Bacteria

• Bacteria are prokaryotes. The genetic material in
  the cells is not contained in a nucleus.

15
Population Explosion
- Bacteria

• Suppose a bacterium reproduces by binary fission
  every 20 minutes. The new cells survive and
  reproduce at the same rate. This graph shows how
  the bacterial population would grow from a single
  bacterium.

16
Population Explosion
- Bacteria

• Reading Graphs
• What variable is being plotted on the horizontal
  axis? What is being plotted on the vertical axis?

• Horizontal axistime (minutes) vertical
  axisnumber of bacterial cells.

17
Population Explosion
- Bacteria

• Interpreting Data
• According to the graph, how many cells are there
  after 20 minutes? One hour? Two hours?

• 2 cells after 20 minutes
• 8 cells after one hour
• 64 cells after two hours.

18
Population Explosion
- Bacteria

• Drawing Conclusions
• Describe the pattern you see in the way the
  bacterial population increases over two hours.

• The number of cells doubles with each division.

19
Population Explosion
- Bacteria

• Predicting
• Do you think the bacterial population will
  continue to grow at the same rate? Why or why not?

• Not likely. The bacteria will continue to
  reproduce at this rate only as long as the
  conditions are favorable.

20
Building Vocabulary
- Bacteria

• After you read the section, reread the paragraphs
  that contain definitions of Key Terms. Use all
  the information you have learned to write a
  definition of each Key Term in your own words.

Key Terms
Examples
bacteria
If Leeuwenhoek had owned one of the high-powered
microscopes in use today, he would have seen the
single-celled organisms known as bacteria in
detail.
A bacterial cell may also have a flagellum, a
long, whiplike structure that helps a cell to
move.
Asexual reproduction is a reproductive process
that involves only one parent and produces
offspring that are identical to the parent.
An endospore is a small, rounded, thick-walled,
resting cell that forms inside a bacterial cell.
The process of breaking down food to release its
energy is called respiration.
During pasteurization, food is heated to a
temperature that is high enough to kill most
harmful bacteria without changing the taste of
the food.
Sexual reproduction involves two parents who
combine their genetic material to produce a new
organism, which differs from both parents.
cytoplasm
The region inside the cell membrane, called the
cytoplasm, contains a gel-like material.
Bacteria reproduce by a process called binary
fission, in which one cell divides to form two
identical cells.
These bacteria, which live in the soil, are
decomposersorganisms that break down large
chemicals in dead organisms into small chemicals.
ribosome
Located in the cytoplasm are tiny structures
called ribosomes, chemical factories where
proteins are produced.
During a process called conjugation, one
bacterium transfers some of its genetic material
to another bacterium through a thin, threadlike
bridge that joins the two cells.
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More on Bacteria
- Bacteria

• Click the PHSchool.com button
• for an activity about bacteria.

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End of SectionBacteria
23
Common Bacterial Diseases
- Viruses, Bacteria, and Your Health

• Many bacterial diseases can be cured with
  antibiotics.

24
Common Viral Diseases
- Viruses, Bacteria, and Your Health

• Unlike with bacterial diseases, there are
  currently no medications that can cure viral
  infections.

25
Using Prior Knowledge
- Viruses, Bacteria, and Your Health

• Look at the section headings and visuals to see
  what this section is about. Then write what you
  already know about diseases caused by viruses and
  bacteria in a graphic organizer like the one
  below. As you read, write what you learn.

What You Know

1. You can catch a cold from somebody who has one.
2. Some diseases can be treated with medicines.

What You Learned

1. You can catch diseases through contact with an
   infected person, a contaminated object, an
   infected animal, or an environmental source.
2. Antibiotic resistance results when some bacteria
   are able to survive in the presence of an
   antibiotic.

26
Antibiotic Resistance
- Viruses, Bacteria, and Your Health

• Click the Video button to watch a movieabout
  antibiotic resistance.

27
Links on Infectious Diseases
- Viruses, Bacteria, and Your Health

• Click the SciLinks button for links on infectious
  diseases.

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End of SectionViruses, Bacteria, and Your Health
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Graphic Organizer
Nonliving
Can be useful
Treated with antibiotics
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End of SectionGraphic Organizer