18.1 Studying Viruses and Prokaryotes

MAIN IDEABacteria have various strategies for survival.The strategies that prokaryotes use to survive and to transfer genes have madethem very successful at adapting quickly to almost any habitat.Gene Exchange in ProkaryotesProkaryotes reproduce by a type of cell division called binary fission, whichmeans “division in half.” While the chromosome copies itself, the cell grows.When the cell has about doubled in size, its plasma membrane grows inwardand divides the cell into two equal-sized daughter cells. Each daughter cell willcontain a complete copy of the parent cell’s genes.Although prokaryotes reproduceasexually, they are still able to exchangegenetic material in several ways. In oneprocess, called conjugation (kahn-juh-GAY-shuhn), prokaryotes can exchangeparts of their chromosomes through ahollow bridge of pili formed to connecttwo or more cells.Surviving Harsh ConditionsDuring conditions unfavorable forVISUAL VOCABIn conjugation, genetic materialtransfers between prokaryotes, producinggenetic variation. A conjugationbridge forms from the donor cell to arecipient cell.conjugation bridgesurvival, some bacteria can produce anendospore, a specialized cell with a thick,TEM; magnification 6000protective wall. To form an endospore,the bacterium copies its chromosome and produces a wall around the copy.This thick wall around the bacterial DNA helps it survive harsh conditionssuch as drying out, temperature change, and disinfectants. Endospores can lastfor centuries. Some have even been found in Egyptian mummies!Connect Why are disinfectants alone not enough to kill all types of bacteria?18.4 ASSESSMENTONLINE QUIZClassZone.comREVIEWINGMAIN IDEAS1. What are the three most commonshapes of bacteria?2. Why are bacteria and archaea classifiedinto different domains?3. Prokaryotes will take up foreignDNA. How is this characteristic usedin genetic engineering?CRITICAL THINKING4. Infer Scientists estimate that only1 percent of prokaryotes can begrown in the lab. What does thissuggest about our knowledge ofbacteria and archaea?5. Synthesize Prokaryotes multiply bybinary fission, which simply divides acell in two. Why are mutations andconjugation important for naturalselection in prokaryotes?Connecting CONCEPTS6. Health Bacteria in your mouthconvert foods containing sugarand starch into acids that canthen cause cavities in yourteeth. These bacteria will bepresent even if you brush yourteeth, floss, or use mouthwash.So why are these hygienehabits so important?558 Unit 6: Classification and Diversity