For the purposes of this book, simply choose the letter beside the appropriate square. This question tests how well you understand the organization of the passage, as well as grammatical connections between sentences. | Chapter Read the following passage. Then fill in the diagram with the information that you read. Track 48 .g vi I JI J h j Microbes or tiny organisms make up the majority of the Earth s living biomass. They are invisible to the naked eye. Therefore biologists must use specific methods to study and measure the activity of these organisms. Although their minute size makes them somewhat difficult to observe scientists have developed two tools for studying microbial activity. These are radioisotopes and microelectrodes. A radioisotope is an atom with an unstable nucleus. It releases its excess energy as radiation. The radiation chemically alters the microorganism. When used to study microbes this radiation allows microbiologists to assess the chemicals released. A Radioisotopes can be used to study microbial activity in a variety of environments. B They are often used in the field of medicine for certain tests and treatments. For example doctors can inject a radioisotope into a patient suspected to have cancer. The patient then undergoes a PET scan a C The radioisotope highlights the tumors on the scan. This aids doctors in determining the exact cause of a medical condition. Subsequently they can treat the illness. Radioisotopes can also be used to eliminate harmful bacteria in foods n D Some types of meat contain parasites or pathogenic bacteria. Radioactive isotopes can target the specific bacteria and irradiate them. This kills the bacteria without harming the rest of the meat. A microelectrode is an electrical device that can deliver an electric current to a non-metallic surface. Microelectrodes can be used to detect metabolic or energy-producing processes in microbes. A In one study biologists tried to determine why one type of bacteria was able to multiply so quickly in a certain environment a 8 They used microelectrodes to measure the levels of carbon dioxide and oxygen at different depths in a minute environment. They discovered that oxygen was depleted in the
