The World of Microbes

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$Discrete Math Chapter 14 Descriptive Statistics 14.2 Exercise 1 ...$

The World of Microbes • Activity 45Figure 2: Some Common Types of BacteriaShape Examples Ecological RolesDiplococci(pairs of cocci)cause pneumoniasphere Staphylococci are normally present on human skin;(clusters of cocci)some cause boils and infectionsStreptococci(chains of cocci)are used to make yogurt and cheese; causestrep throatrodBacilli (rods)Mycobacteria(chains of bacilli)decompose hay; are used to make cheese,yogurt, pickles, and sauerkraut; arenormally present in the human digestivetract; cause diarrhea; cause anthrax incattle and sheepcause tuberculosis; are found normally insoil and water.curved rod Vibrio cause cholera; help break down sewageshort spirals Spirilla are decomposers in both fresh andsalt waterlong spirals Spirochete cause syphilis; are decomposersbranched chain Actinomyces produce several antibiotics; were onceclassified as fungiCocci are spherical bacteria; the singular of cocci is coccus.➢© 2006 The Regents of The University of California.Created by SEPUP, Lawrence Hall of Science, Berkeley, California. Adapted with permission. All rights reserved.C-73
Activity 45 • The World of MicrobesViruses: A Group ApartViruses are not living organisms. Unlike protists, bacteria, and allother living organisms, viruses are not made up of cells. They areunable to grow or reproduce independently or carry out the functions,such as respiration, that living organisms do. Instead, viruses rely onthe cells of living organisms for their reproduction. It is for this reasonthat we say infectious diseases are caused by microbes, and notmicroorganisms.virusbacteriumprotistFigure 3: Comparing Average Sizes of MicrobesThese are relative, not actual, sizes of microbes. An average bacterium is actually muchsmaller than the virus shown here.STOPPING TO THINK 3a. Why are viruses not considered to be microorganisms?b. Look at Figure 3, “Relative Sizes of Microbes.” How do the sizesof protists, bacteria, and viruses compare?c. Which do you think cannot be seen with a classroom microscope?How do we know viruses exist? The existence of viruses was first suggestedin 1898, nearly 45 years before they were first seen. In 1895,Dutch scientist Martinus Beijerinck (BY-er-ink) began experimentingwith the tobacco plant. He was studying a plant disease that hebelieved to be infectious. By this time, scientists were familiar withprotists and bacteria, so Beijerinck began searching for a bacteriumthat might be causing this disease. But he could not find one. Yet hisexperiments demonstrated that the disease could be passed fromplant to plant, so he concluded that the disease was caused by amicrobe. Since it wasn’t a protist or a bacterium, he called it a virus,which means “poison” in Latin.C-74© 2006 The Regents of The University of California.Created by SEPUP, Lawrence Hall of Science, Berkeley, California. Adapted with permission. All rights reserved.
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The World of Microbes

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