- 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.

Practice Problem Measure the diameter of a quarter. 2.4 cm - Viruses Diameter

Practice Problem Measure the diameter of a CD. 12 cm - Viruses Diameter

- Viruses How Viruses Multiply • Hidden viruses “hide” for a while inside host cells before becoming active.

- Viruses 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.

- Viruses 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.

End of Section:Viruses

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

- Bacteria Population Explosion • 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.

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

2 cells after 20 minutes; 8 cells after one hour; 64 cells after two hours. Interpreting Data: According to the graph, how many cells are there after 20 minutes? One hour? Two hours? - Bacteria Population Explosion

The number of cells doubles with each division. Drawing Conclusions: Describe the pattern you see in the way the bacterial population increases over two hours. - Bacteria Population Explosion

Not likely. The bacteria will continue to reproduce at this rate only as long as the conditions are favorable. Predicting: Do you think the bacterial population will continue to grow at the same rate? Why or why not? - Bacteria Population Explosion

Key Terms: Key Terms: Key Terms: Examples: Examples: Examples: flagellum endospore asexual reproduction respiration pasteurization sexual reproduction binary fission decomposer conjugation - Bacteria Building Vocabulary • 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 A bacterial cell may also have a flagellum, a long, whiplike structure that helps a cell to move. 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. 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. During pasteurization, food is heated to a temperature that is high enough to kill most harmful bacteria without changing the taste of the food. The process of breaking down food to release its energy is called respiration. 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 decomposers—organisms 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.

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

End of Section:Bacteria

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

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

- Viruses, Bacteria, and Your Health Using Prior Knowledge • 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.

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

End of Section:Viruses, Bacteria, and Your Health

Graphic Organizer Can be useful Nonliving Treated with antibiotics

End of Section:Graphic Organizer

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