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
All viruses have two basic parts: a protein coat that protects the virus and an inner core made of genetic material. Some viruses are surrounded by an outer membrane envelope.

4. How Viruses Multiply - Viruses
Active viruses enter cells and immediately begin to multiply, leading to the quick death of the invaded cells.

5. - Viruses
Diameter
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. How Active Viruses Multiply
Sequencing
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.

10. How Hidden Viruses Multiply
Sequencing
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.
Virus’s genetic material becomes part of cell’s genetic material.
Cell produces viral proteins and genetic material.
Viruses are assembled.
Cell bursts, releasing viruses.

11. End of Section: Viruses

12. The Bacterial Cell - Bacteria
Bacteria are prokaryotes. The genetic material in the cells is not contained in a nucleus.

13. 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.

14. Population Explosion - Bacteria Reading Graphs:
What variable is being plotted on the horizontal axis? What is being plotted on the vertical axis?
Horizontal axis–time (minutes); vertical axis–number of bacterial cells.

15. 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.

16. 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.

17. 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.

18. 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:
flagellum
respiration
binary fission
endospore
Key Terms:
Examples:
pasteurization
decomposer
asexual reproduction
Key Terms:
Examples:
sexual reproduction
conjugation
Key Terms:
Examples:
bacteria
An endospore is a small, rounded, thick-walled, resting cell that forms inside a bacterial cell.
Asexual reproduction is a reproductive process that involves only one parent and produces offspring that are identical to the parent.
A bacterial cell may also have a flagellum, a long, whiplike structure that helps a cell to move.
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.
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.
cytoplasm
The region inside the cell membrane, called the cytoplasm, contains a gel-like material.
Sexual reproduction involves two parents who combine their genetic material to produce a new organism, which differs from both parents.
Bacteria reproduce by a process called binary fission, in which one cell divides to form two identical cells.
ribosome
These bacteria, which live in the soil, are decomposers—organisms that break down large chemicals in dead organisms into small chemicals.
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.

19. More on Bacteria - Bacteria Click the PHSchool.com button
for an activity about bacteria.

20. End of Section: Bacteria

21. Common Bacterial Diseases
- Viruses, Bacteria, and Your Health
Common Bacterial Diseases
Many bacterial diseases can be cured with antibiotics.

22. Common Viral Diseases - Viruses, Bacteria, and Your Health
Unlike with bacterial diseases, there are currently no medications that can cure viral infections.

23. 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
You can catch a cold from somebody who has one.
Some diseases can be treated with medicines.
What You Learned
You can catch diseases through contact with an infected person, a contaminated object, an infected animal, or an environmental source.
Antibiotic resistance results when some bacteria are able to survive in the presence of an antibiotic.

24. Links on Infectious Diseases
- Viruses, Bacteria, and Your Health
Links on Infectious Diseases
Click the SciLinks button for links on infectious diseases.

25. End of Section: Viruses, Bacteria, and Your Health

26. Graphic Organizer
Nonliving
Can be
useful
Treated with
antibiotics

27. End of Section: Graphic Organizer