KEY CONCEPTS AND PROCESS SKILLS. 2. Most infectious diseases are caused by microbes.

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1 Who s Who? to 1 50-minute session ACTIVITY OVERVIEW I N V E S T I O N I G AT SUMMARY Cards with images of the major groups of disease-causing microbes (s, bacteria, and es) are presented. Students classify these cards into six classes according to their characteristics. KEY CONCEPTS AND PROCESS SKILLS 1. All living things are composed of microscopic units called cells. Protists and bacteria are single-celled microbes. 2. Most infectious diseases are caused by microbes. 3. The category of microbes includes microorganisms, such as bacteria and s, and also es, which are not considered to be alive. 4. Characteristics that distinguish microbes include size, shape, and structure. Differences between s, bacteria, and es include whether they are cells, the presence or absence of a nucleus, and relative size. KEY VOCABULARY bacteria cell cell membrane cytoplasm microbe nucleus magnify/magnification C-193

2 Activity 44 Who s Who MATERIALS For the teacher Transparency 44.1, Key to Microbe Identities * 1 overhead projector For the class 8 sets of Classification Cards For each group of four students 1 set of Micro-Life Cards *Not supplied in kit TEACHING SUMMARY Getting Started 1. Review students observations of microbes in Activity 43, Microbes Under View. Doing the Activity 2. Student groups work together to classify Micro-Life Cards according to the five-kingdom classification scheme. 3. The class discusses the classification of the microbes on the Micro-Life Cards. Follow-Up 4. The class discusses criteria used to classify microbes. BACKGROUND INFORMATION Disease-Causing Microbes There are many disease-causing agents, including animals, fungi, bacteria, s, and es. Microbial species of fungi cause athlete s foot and yeast infections such as thrush. Animals such as tapeworms also can infect humans. However, this activity focuses on three groups of disease-causing agents: s, bacteria, and es. Protists are single-celled microorganisms that contain a nucleus (and other cell compartments). Trypanosoma lewisi is a that causes disease in rats. It belongs to the same genus as Trypanosoma brucei, the that causes African sleeping sickness in C-194 Science and Life Issues

3 Who s Who Activity 44 humans. Both trypanosomes have a flagellum, a tail-like structure used for locomotion. Different species of Paramecium live in freshwater and saltwater environments, where they feed on bacteria, algae, and other s. Paramecia move by beating their cilia, small structures that look like tiny hairs on the outside of the cell. Amoeba proteus is another. Like Paramecia, Amoebae eat other microorganisms found in water and also in soil. Some Amoebae do cause disease: Entamoeba histolytica causes dysentery. Amoebae move by extending portions of their body (known as pseudopodia, or false feet ). Bacteria are single-celled microorganisms that lack a nucleus (as well as other membrane-bound organelles). Escherichia coli (E. coli) is one bacterial species that is familiar to most people. Some strains of E. coli are common residents of the human digestive system and are harmless. However, other strains of E.coli can cause disease, including some well-known recent outbreaks of an especially virulent strain that can be transmitted by food, animals, and in swimming pools. Viruses are not classified as organisms because they are not free-living cells. Instead, they have a core of genetic material surrounded by a protein coat. Viral diseases include colds, flu, chickenpox, hepatitis, and AIDS. Viruses introduce their genetic material into the host cell. The host cell then reproduces the, and new es are released to continue the infection. Classification Systems The approach to classifying organisms continues to develop based on new evidence. In this activity, students use the five-kingdom approach to classifying organisms. In the next activity, they learn the latest approach to the classification of microbes. C-195

4 Who s Who Activity 44 TEACHING SUGGESTIONS GETTING STARTED 1. Review students observations of microbes in Activity 43, Microbes Under View. Teacher s Note: You may wish to assess students on either element ( Task Management or Shared Opportunity ) of the GROUP INTERACTION (GI) variable during this activity. If your students do not have much experience with classification, you may want to prepare them for this activity by having them classify coins. They will realize that coins can be classified by different criteria (size, color, picture, etc.) and that different criteria can lead to different classification schemes. Tell students that they will have an opportunity to get a closer look at microbes and to develop a system for classifying them. Ask, What kinds of differences have you observed so far in your observations of microbes? Their answers are likely to include differences in size, shape, and whether they could observe any internal details, such as the presence of a nucleus. Ask, If you were unable to see a nucleus, can you be certain that none was present? Help students realize that they cannot be sure; different stains or higher magnification might reveal more detail. Explain that they will use photos and drawings obtained at higher magnification to help them refine their classification of the microbes. DOING THE ACTIVITY 2. Student groups work together to classify Micro-Life Cards according to the fivekingdom classification scheme. Each group of students should receive a complete set of the 9 Micro-Life Cards. Students have an opportunity to view and classify pictures of actual disease-causing agents as well as other organisms. Have them turn to the Procedure in the Student Book and follow the directions. Students are asked to first observe the cards. Do not tell the students how to classify; allow them to make their own observations and decisions about what criteria to use for classification. The cards illustrate the shape and external structure as observed through an electron microscope as well as a sketch of the internal structure of each microbe. The size of each microbe in microns is provided on the card. One micron is one thousandth of a millimeter (0.001 mm), or one millionth of a meter ( m), also expressed as 10-6 meters. Each card also states whether the agent is a single cell or not a cell. (This activity does not include any multicellular organism cards. They will be added to the classification scheme in Unit E, Ecology, in Science and Life Issues.) Students should work together to group the various cards and record the groups that were formed. Most importantly, students should record the characteristics used to form each of the groups. If students are having problems, make suggestions to get them started, but allow them to work as independently as possible. Allow students to view the work of other groups, either by having them circulate around the room or by having a few groups present their classification systems. After groups have completed their classifications, provide them with a set of the 6 Classification Cards. Have them complete Step 7 of the Procedure and record in their notebooks what kinds of changes in classification they had to make. C-197

5 Activity 44 Who s Who Teacher s Note: Students will find that the Classification Cards include cards for animals, plants, and fungi. However, none of their Micro-Life Cards include examples from these categories of organisms. Explain to students that they will have a chance to classify more organisms and use these categories in Unit E, Ecology, of Science and Life Issues. 3. The class discusses the classification of the microbes on the Micro-Life Cards. Discuss students final classification schemes. Explain that they are based on a system widely adopted in Before then, all organisms were classified as either animals or plants. Point out that though the Classification Cards include five kingdoms plus the non-living es, there are other possible classification schemes. Classification schemes can be modified based on additional information and should be evaluated based on usefulness. Discuss the benefits of a classification scheme. At the most basic level, it allows scientists all over the world to communicate regarding organisms. Classification schemes first arose as a way to create an orderly system of categories of organisms that could be grouped for study. As new evidence about similarities and differences among organisms is discovered, the classification systems are modified. Most scientists now favor a new system, to be discussed in Activity 45, The World of Microbes. However, the five-kingdom system is helpful for students in thinking about the diversity of organisms. As a class, review how microbes are classified. A key to the disease-causing agents is provided in Transparency 44.1, Key to Microbe Identities. You can use this information to review which microbes are s, bacteria, or es. The disease examples given are sometimes for the exact microbe depicted on the card, and sometimes for a microbe with a very similar appearance and internal structure. You may wish to mention that other groups of organisms, namely fungi and animals, can cause diseases. Some examples are the fungi that cause athletes foot, the mites that cause scabies, and parasitic worms, such as roundworms and tapeworms. Treatments for these diseases depend on the biology of the disease-causing organism. In some cases, treatment is very difficult. For example, worm parasites are much more closely related to humans than bacteria and es. For this reason, it is very difficult to get rid of these parasitic infections without causing side effects for the human host. Drug therapy for worm infestations often requires hospitalization, making prevention a much better option. FOLLOW UP 4. The class discusses criteria used to classify microbes. Use this investigation to reinforce some of the key parts of cells, such as the cell membrane, nucleus, cytoplasm, and cell wall. Some of the other structures, such as the cilia and flagella used for locomotion by some s and bacteria, can also be mentioned briefly, but are not a major focus of this activity. In the case of es, the absence of a cellular structure is one key criterion that leads to its classification as a non-living microbe. C-198 Science and Life Issues

6 Who s Who Activity 44 SUGGESTED ANSWERS TO ANALYSIS QUESTIONS 1. How could knowing the structure and classification of disease-causing microbes help scientists fight a disease? Students may suggest that treatments such as shots or drugs may work against different groups of microbes. You may wish to expand on this and explain that if scientists know the structure of a microbe, they can search for chemicals (or other methods) to attack specific structures of the microbe. For example, some antibiotics attack the membranes of bacteria, while others attack internal structures and prevent the bacteria from reproducing. Ask students what would happen if scientists decided to try to attack a part of a microbe that was very similar to a structure in human cells. The human cells might be damaged by the drug that was supposed to be killing the microbe. This is one reason why many drugs have side effects. Scientists try to find drugs that target unique features of the disease-causing microbe that humans do not share. That way, the drug will attack only the microbe. 2. How did your system of classification compare to the Classification Cards? Students may have used various features, such as internal structures, external structures, and/or size, to classify the organisms. These may or may not correspond to the conventional five-kingdom system. 3. Look back at the generalized animal cell in Figure 1 in Activity 42, A Closer Look on page C-59. Explain how this drawing of a cell is similar to or different from the structure of each of the following groups of microbes: a. s Like the drawing, s are made up of a single cell containing a nucleus, cytoplasm, and a cell membrane. b. bacteria Like the drawing, bacteria are made up of a single cell with a cell membrane and cytoplasm. However, they lack the nucleus shown in the figure. c. es Viruses are not made of cells, so there is less basis for comparison between the drawing and es. However, es do have an external coat, which acts like the cell membrane, to define the boundary of the. C-199

7 Key to Microbe Identities 2006 The Regents of the University of California Card Number Type of Microbe 1 bacterium 2 bacterium bacterium 9 Genus (or type) Disease(s) It Can Cause coccus (round) strep throat bacillus (rods) tuberculosis Paramecium none tobacco mosaic plant diseases adeno colds Amoeba amoebic dysentery influenza flu spirillum rat-bite fever, meningitis Trypanosoma sleeping sickness Science and Life Issues Transparency 44.1 C-201