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Q How are bacteria helpful to humans? These bacteria live in the lining of an esophagus, the tube that leads from your mouth to your stomach. Only a few years ago, it was thought that nothing could survive in an esophagus, but the entire digestive tract is home for many types of bacteria. Being a home to bacteria isn’t bad, though. Some doctors hypothesize that these bacteria may protect us from some throat and stomach cancers.

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USING LANGUAGE Your Turn Cause and Effect In biological processes, one step In the following sentences, identify the cause and effect. leads to another step. When reading, you can recognize 1. Disease spreads easily from one population to another cause-and-effect relationships by words that indicate a because people travel frequently. cause and result, such as because, so, consequently, and 2. HIV infects white blood cells. Consequently, the as a result. immune system becomes vulnerable to disease.

Chapter 18: Viruses and Prokaryotes 527 CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” Unit 528 FIGURE 1.1 FIGURE prion pathogen VOCABULARY and influenza human immunodeficiency virus(HIV) of viruses incausing diseases suchas reproduction, anddescribe therole of viruses to c (co charac are this lored TEM; magnification 6000 magnification TEM; lored

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y proteins. Viruses are much also than smaller most cells, as you in can see on own. their Instead, living need cells to they help reproduce them and make have genes and can reproduce. Unlike cells, however, cannot viruses reproduce living things?respond living Like cells, viruses to environment. their Viruses clearly living things,have since they each of traits the of life. But are viruses Viroids 1.2. FIGURE of code the life. Prokaryotes—such as bacterium the shown in respond to environments. their contain also They genetic material that carries ab know what exactly are. they A You are probably familiar and with terms the virus bacteria, but you may not can stunt growth the of plants. Viroidspollen. have had amajor economic impact on agriculture they because single-stranded RNA without aprotein coat. are They or through passed seeds agent, or organism or that particle can an cause infectious an is called infectious disease hand, are one-celled microorganisms that cause can also infection. Any living strand of DNA or RNA surrounded by aprotein on coat. other the Bacteria, system of biological classification. many differences. are In viruses not fact, even given a place Linnaean inthe MAI MAI C Viruses, ilities to reproduce, to nutrients use and energy, to grow and develop, and to o You have that learned living all things share key characteristics: certain the A viro N n N ID c ID are infectious that particles inplants. cause disease Viroids are made of e p pathogen. E While viruses have While viruses key traits similar have to living also cells, they id has even less in common with living things than do viruses. E

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FIGURE 1.2 Relative Sizes of Cells and Infectious Particles Although eukaryotic and prokaryotic cells can be microscopic, 1 nanometer (nm) = one billionth of a meter they are large in comparison to viruses, viroids, and prions. 100 nm

eukaryotic cells viroids 10,000–100,000 nm 5–150 nm viruses 50–200 nm prokaryotic cells 200–10,000 nm prion 2–10 nm

Infer Why are viroids and prions sometimes called subviral particles?

At the boundary between living and nonliving, perhaps the strangest entity R E ADI n g TOO LB ox of all is the prion. A prion (PREE-ahn) is an infectious particle made only of proteins that can cause other proteins to fold incorrectly. When proteins TAKING NOTES Use a two-column chart to misfold, the protein will not work properly. Prions are unusual in that they are take notes on viruses, infectious yet have no genetic material. They play a part in certain diseases of viroids, and prions. the brain such as mad cow disease, known to scientists as bovine spongiform Main Idea Detail encephalopathy, or BSE. Humans may become infected with BSE when they eat Virus meat from animals that are infected. Food safety laws in the United States, however, try to reduce the risk of infection. Creutzfeld-Jakob (KROYTS-fehlt Viroid YAH-kawp) disease (CJD), another brain disease that affects humans, is also Prion associated with prions. Prion diseases can incubate for a long time with no effect on their host. However, once symptoms appear, they worsen quickly and are always fatal, because the body has no immune response against a protein. Synthesize Why are viruses, viroids, and prions not included in the Linnaean system of biological classification?

Self-check Online HMDScience.com 18.1 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. What are the main differences 3. Infer Prions were not widely known Medicine between living cells and viruses? to be infectious agents until the 5. To multiply, viruses must take 4c 1980s. Give two reasons why this over the functions of the 2. Viruses, viroids, prions, and some might be so. cells they infect. Why does bacteria can all be considered 4. Apply An RNA-based disease this make it difficult to make spreads through pollen. Is it likely due effective antiviral drugs? pathogens. What do all pathogens 4c have in common? to a virus, viroid, or prion? Explain.

Chapter 18: Viruses and Prokaryotes 529 CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” Unit 530 D A T A ANALYSIS

6: and Continuous Data,” thedifference between these two data types. convey different information. Recall from theData Analysis activity, “Discrete Different methodsofdisplaying data, suchasbargraphs orlinegraphs, often ofmonitoring part important trends anddetermining acourse oftreatment. Collecting data onthespread ofinfectious disease inapopulation isan Representation Data Choosing

T Table 1.S California Texas New Jersey Georgia Illinois Florida New York Virginia Pennsylvania CarolinaNorth Classification andDiversity

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(t) ©Duncan Smith/Photo Researchers, Inc.; (b) ©Norm Thomas/Photo Researchers, Inc. FIGURE 2.1 FIGURE prophage infection lysogenic infection lytic VOCABULARY and influenza human immunodeficiency virus(HIV) of viruses incausing diseases suchas reproduction, anddescribe therole of viruses to cells, describe viral virus identified by scientists. virus (TMV).TMVwas thefirst leaf infected by tobacco mosaic compare ahealthy leaf anda 4Ccompare thestructures 18.2

These pictures Infected leaf Healthy leaf 4C Viral Structure andReproduction host cells. ways in and shape in differ ofenteringViruses structure, andhave several different ways to get into theirhosts. Also like computer viruses, viruses oflivingthings can besimple orcomplex in networks from onecomputer to another, humanviruses pass from person to person. living things pass from onehost to While thenext. computer viruses pass through Just like thecomputer viruses that you hear aboutinthenews, viruses that affect Your to World Connect Ke

y finding that many of unknown diseases causes explained could be by viruses. and laid groundwork Beijerinck the for more discoveries. Scientists began from viruses, particles for Latin the “poison.” The observations of Ivanovsky that tiny caused withininfection, particles extracts the andthe he called work. He showed agent that disease the through passed agar gel. He proposed ofunknown type organism? pass onWascould still disease. the bacterium? Or anew was this it some filter pores enough small to strain out and bacteria found that extracts the able to prove it. Ivanovsky tobacco leaves of extracts diseased passed through capsid. a virion, is made up of genetic material surrounded by aprotein a shell called Viruses have an amazingly simple basic structure. particle, called Asingle viral T 2.1, FIGURE on leaves affected of tobacco or tomato plants. Mosaic shown disease, in tion. He was studying tobacco named mosaic disease, for pattern scar the left Russianin 1892when scientist Dmitri Ivanovsky made asurprising observa- The that idea infectious agents was afairly cause diseases concept certain new of from avirus, which spiky structures of proteins and sugars may stick out. surrounded by alipid envelope. A lipid envelope is protective the outer coat MAI MAI C he Structure of Viruses of Structure he

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Chapter 18:Viruses andProkaryotes

531 CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” 532

Unit 6:Clas types of viruses shown above? shown viruses of types Contrast and Compare T 2.2 FIGURE he different proteins that make upaviral capsid give viruses avariety ofshapes. en (colored TEM; magnification 255,000 magnification TEM; (colored The envelope isshown inorange. virus,often haveinfluenza spikes. Enveloped viruses, suchasthis capsid v sification andDiversity e lo

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4C The s Viru 65,000 magnification TEM; lope. (colored helical virusthat also hasanenve- rabies virusisanexample ofa coiled shapecalled The ahelix. Some viruses have narrow, along, h nucleic acid ses canses only reproduce afterhave they infectedhost cells. Viruses are tructure and shape play of viruses an important role inhow they e lical 3 ) capsid surface proteins FIGURE 2.2. FIGURE envelope lipid proteins surface p (computer illustration) animals. (computer causes foot-and-mouth disease in like theoneshown here that Polyhedral viruses are many-sided, olyh e dral capsid nucleic acid

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(t), (inset) ©Eye of Science/Photo Researchers, Inc. Viruses cause two types ofinfections. causeViruses two types for their functions. Summarize

mammals. The T-bacteriophage shown in Escherichia coli, commonly bacteria the found intestines inthe of that One example bacteria. infect is T-bacteriophage the that infects Neither path for is good host. the Instead of destroying house, the phage the becomes apermanent houseguest. house it when leaves. The other path of infection is somewhat more subtle. household,the eats refrigerator, of inthe all food the and blows then up the ing mostthe , the studied viruses, in pathways of infection are pathways similarThese for viruses. all are shown for The ways enter inwhich viruses and leave may acell vary, but two basic targetinside viruses nucleus the cell, the eukaryotic of cell. the into cell’s the cytoplasm. that HIVis avirus enters cellsway. inthis Once fusing with plasma the membrane of host the and cell releasing capsid the are Ifmolecules. viruses the enveloped, enter can also they ahost by cell intoecules by acell forming vesicles, or membrane-bound around sacs, the that is an endocytosis of Recall active method endocytosis. bringing mol- of entering host the cell. For example, may viruses enter these cells by the Viruses that eukaryotes infect differfrom bacteriophages methods intheir that Infect Viruses “phages.” One group is bacteriophages, the of viruses simply often called Bacteria that Infect Viruses stranded or double-stranded, and linear, circular, or segmented. RNA but never The both. genetic material single- can of be viruses always main the genetic material, can have avirus either DNA or like aspring or helix. sh is found. like asyringe, injecting its genes into host the cell’s cytoplasm, where its DNA punches through injecting phage’s wall, the cell the DNA. The phage works The sheath wall. down tail cell of contracts, part bacterial the and core tail the cell. After attachment, bacteriophage’s the releases tail an enzyme that breaks geneticthe material. The and tail its spikes help attach to host the virus the connected to along protein with tail spiky footlike The capsid fibers. contains MAI aped and often strandlike have viruses capsids shaped incoils, Once inside host the cell, phages follow one of two general paths incaus- In co In capsids some viruses, form Rod- polyhedral. a20-sided disease. Indisease. one path, phage the behaves like houseguest. a bad It takesover N ID ntrast to prokaryotes and eukaryotes, inwhich DNA is

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cribe how the structures of a bacteriophage are well-suited 4C 4C E uka (bak-TEER-ee-uh-fayj-ihz) are viruses ryotes FIGURE 2.3 FIGURE 2.3 FIGURE 2.4. FIGURE has capsid a20-sided large photo 25,000 photo large magnifications: SEM; colored FIGURE 2.3 FIGURE shown below. structure ofabacteriophage is outside thecell (inset). Theunique rium, theprotein coats remain genetic material into thebacte- bacterium. While their injecting bacteriophages attacking coli anE. DNA Chapter 18:Viruses andProkaryotes 3 ; inset 38,000 inset ;

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FIGURE 2.4 General Pathways of Viral Infection

A lytic infection results in the lysis, or breaking apart, of the host cell and release of new viral particles. A lysogenic infection does not destroy the host cell.

host bacterium

Lytic infection

The bacteriophage attaches and injects its DNA into a host bacterium.

The host bacterium breaks apart, or lyses. Bacteriophages are able The viral DNA to infect new host cells. forms a circle.

The viral DNA directs the host cell to produce new viral parts. The virus may enter the The parts assemble into new ­lysogenic cycle, in which the bacteriophages. host cell is not destroyed.

Lysogenic infection

The viral DNA is called a ­prophage when it combines The prophage may leave with the host cell’s DNA. the host’s DNA and enter the lytic cycle.

Although the prophage is not Many cell divisions produce a active, it replicates along with colony of bacteria infected the host cell’s DNA. with prophage.

CRITICAL Why are no capsids or tail sheaths made during 4c VIEWING a lysogenic infection?

534 Unit 6: Classification and Diversity DO NOT EDIT--Changes must be made through “File info” CorrectionKey=A

Lytic Infection A lytic infection (LIHT-ihk) is an infection pathway in which the host cell R E ADI N G TO OLB ox bursts, releasing the new viral offspring into the host’s system, where each then infects another cell. VOCABULARY The term lytic comes from the • When the viral DNA enters the host cell, it takes over control of the host’s Greek word lutikos, meaning own DNA, turning on the genes necessary to copy the viral genes. “able to loosen.” The word lysis • Under direction of the viral genes, the host’s DNA undergoes transcription is often used in biology to describe a cell breaking apart. and translation, and produces capsids and enzymes. The enzymes then help in the copying of the virus’s DNA. • Using energy from the host cell, the capsids and viral DNA assemble into new virions. Viral enzymes dissolve the host cell membrane, releasing the new virus particles into the host’s bloodstream or tissues—and destroying the host cell in the process.

Lysogenic Infection In a lysogenic infection (ly-suh-JEHN-ihk), a phage combines its DNA into the host cell’s DNA. • After entering the host cell, the viral DNA combines with the host’s DNA, forming a new set of genes called a prophage. A prophage is the phage DNA inserted into the host cell’s DNA. In organisms other than bacteria, this stage is called a provirus. • The prophage is copied and passed to daughter cells, with the host’s own DNA, when the host cell undergoes mitosis. Although this process doesn’t destroy the cell, it can change some of the cell’s traits. • After the cell has been copied, the prophage faces two possible paths. A trigger, such as stress, can activate the prophage, which then uses the cell to produce new viruses. Or the prophage can remain as a permanent gene. Connect Using the analogy of viral infections resembling houseguests, explain which describes a lytic and which describes a lysogenic infection. 4C

Self-check Online HMDScience.com 18.2 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. Name and describe the main parts of 3. Apply Researchers studying infection Evolution a typical virus. 4C can often grow bacteria more easily 5. If the virus is a foreign 2. What are the differences between a than they can grow viruses. What invader, how is it possible lytic infection and a lysogenic conditions must scientists provide for for the proteins of its capsid infection? Include the effects of viruses to multiply? 4C to match the receptors on each type of infection on the cells of 4. Classify A wart is caused by a virus the host cell’s surface? the host organism in your answer. that may lie dormant for years before Consider natural selection 4C any symptoms appear. Does this in your answer. resemble a lytic or lysogenic infec- tion? Explain. 4C

Chapter 18: Viruses and Prokaryotes 535 CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info” Unit 536 protection to thecell. helpful receptors provide little specific infection, these normally response. Inthecase ofahost- signals andperform anaction in proteins that detect chemical Function that receptors are Recall from Cell Structure and Ce retrovirus vaccine epidemic VOCABULARY and influenza human immunodeficiency virus(HIV) of viruses incausing diseases suchas reproduction, anddescribe therole of viruses to cells, describe viral F cation 10,000 cation culture (yell IGURE CO lls ow)

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y Although they’re unpleasant to have, colds usually last only about one week. canIn mutate cold viruses fact, move as they from one person to another. virus is shownvirus in arethan 200viruses known to cause nuisance. seasonal this One such cold The common cold threatening. Below are afew of many the human caused illnesses by viruses. Viruses can cause symptoms that range from merely bothersome to life- E proteinssurface as keysinto tocell the trick allowing it to enter. almostact like When locks. arrives virus the at host the cell, it its uses own cells haveBody receptors that guard against foreign intruders. receptors These However, targeted the cells don’t just open door the to unwanted this guest. mouth, nose, genital area, eyes, and ears. accident that some of most the common points for of entry infection are the can another take route penetrate skinonly the through an opening such as acut or scrape. Or they organisms it might an be outer skeleton or atough Viruses wall. cell can In vertebrates, first obstacle the must avirus pass is skin,but the inother First Defenses must first pass amajor obstacle. ter target their cells. But to enter host’s the first place, inthe virus the body As you have follow read, viruses two pathways of infection once encoun- they th vaccines. th M MAI xamples Viral of Infections C Vaccines Viruses ai o Onc n I n n N c ID e inside body, the its finds way virus the to its target organ or tissue. d ept

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(tr) ©Reuters/Corbis; (bc) ©NIBSC/Photo Researchers, Inc. di Analyze viruses? other from fferently made every year.made every A proteins on capsids viral makesfor it influenzavaccine necessary anew to be spreadthe ofto control. infection difficult Themutation high rate of surface time infecttypes birds, and are all referred to as avian influenza, or bird flu. Some subtypes may horses, infect pigs, More and whales, seals. sub- than fifteen each year.with flu the people. In United the States, up to 20percent of population the is infected virus oncevirus aperson is infected. inslowingeffective spread the of the infection—has proved somewhat drugs—medications that treat viral combined of antiviral use several made it achallenge to treat. The unusually mutation high rate has encounter day. every HIV’s microorganisms that humans unable to fight off common even the syndrome. Once aperson’s immune system is affected, he or she may be of white cells ultimately blood causes AIDS,acquired immune deficiency body’s own immune response against invasion by microbes. HIV SARS Influenza epidemics. An and reason. with good The spreads flu quickly and can result infrequent local white cells of blood host’s the immune system, as shown in and cells. This new infect stage is alytic ofinfection that disease the destroys leave,The viruses new either by budding or bursting through cell provirus, causing no symptoms to its human host. a lysogenic infection. DNA The viral can remain dormant for years as a stranded DNA enters then nucleus the and combines with host’s the genes as reverse anuses enzyme called transcriptase to make aDNA copy. Double- disappear by middleof the monitored 2003,SARSis still globally. throughout world, the quickly becoming pandemic. Although to it seemed inbreathing.difficulty SARSfirst appeared inAsia inlate 2002. It spread dis make an RNA copy inacell, but a “b ackward,” how which describes retroviruses work. Usually, DNA to is used ease. Itease. has symptoms similar to influenza, such as fever and coughing or At th Whe

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FIGURE 3.4 Viral Diseases Viral Infection symptoms of disease Transmission of Disease U.S. Vaccine Recommendation Chickenpox rash, itchy skin, fever, contact with rash, droplet for children between 12 and 18 months fatigue inhalation Hepatitis A yellow skin, fatigue, contact with contaminated feces for people traveling to infected locations abdominal pain and protection during outbreaks Mumps painful swelling in salivary droplet inhalation for children between 12 and 15 months glands, fever and again at 4 to 6 years Rabies anxiety, paralysis, fear bite from infected animal for veterinarians and biologists in contact of water with wildlife West Nile fever, headache, body ache bite from infected mosquito no available vaccine

MAIN IDEA Vaccines are made from weakened pathogens. Chances are good that you have had vaccinations. In the United States, chil- dren are vaccinated at an early age against diseases such as measles, mumps, rubella (MMR), and chickenpox. Every year, millions of people are vaccinated against influenza. How does a simple shot provide protection against disease? CONNECT TO A vaccine is made from the same pathogen—disease-causing agent—that it Human Biology is supposed to protect against. Vaccines consist of weakened versions of the Vaccines help build up the virus, or parts of the virus, that will cause the body to produce a response. The immune system to prepare for immune system is triggered by the surface proteins of a pathogen. In the host’s exposure to a pathogen by body, the vaccine works by preparing the host’s immune system for a future recognizing its surface proteins. You will learn more about the attack. Vaccines can prevent some bacterial and some viral infections, as immune system in the chapter shown in FIGURE 3.4. Whereas bacterial diseases can also be treated with Immune System and Disease. medicine once they occur, viral diseases are not easily treated. Vaccination is often the only way of controlling the spread of viral disease. Vaccines cause a mild immune response. If the body is invaded again, it will be able to start an immune defense before the virus can cause damage. Apply Before the chickenpox vaccination was available, children were often purposely exposed to the virus at a young age. What was the reason for doing this?

Self-check Online HMDScience.com 18.3 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO Human Biology 1. Name and describe two infectious 3. Infer If a vaccine is in short supply, viruses and a body’s first defense why is it often recommended that 5. People infected with HIV, against infection. 4C older adults and children get vacci- the virus that causes the disease AIDS, can become 2. Briefly describe how a vaccine can nated first? unable to fight off infections prevent some viral infections. 4. Apply Why might getting a flu by organisms that normally vaccination sometimes cause you to do not harm people. Why is get a mild case of the flu? this so? 4C

538 Unit 6: Classification and Diversity CorrectionKey=A DO NOT EDIT--Changes mustbemadethrough “File info”

Stephen Ausmus/Agricultural Research Service/USDA to digest. down plant material for the cow shelter andnutrients, break cow’s stomach. Thebacteria have ria live mutualistically withina study digestion. Anaerobic bacte- four stomachs, allows scientists to into ac FIGURE endospore conjugation flagellum plasmid aerobe facultative aerobe obligate anaerobe obligate VOCABULARY of taxonomic gr plants, andanimals archaea, bacteria, , fungi, 8 ow’s rumen, thefirstofits 4.1 C 18.4 compare characteristics

A “window” made oups, including 8c Bacteria andArchaea ­pro P milliliter of saliva can contain upto bacterial 40million cells. fact, you may have asmany25different typesinyour mouthrightnow. One the environment. Upto 500typesofprokaryotes can live inthehumanmouth.In Humans not only share theenvironment withprokaryotes—for manyspecies,we are Your to World Connect Ke E valuate rokaryotes are widespread on

y facultative aerobe obligate aerobes obligate anaerobe 1 billion (10 about 7billion individuals. In contrast, scientists estimate there are more than and abundant organisms Consider on that Earth. humans are one with species Prokaryotes, which include and bacteria archaea, are most the widespread herbivores such as deer, sheep, and cows, as shown in liveThey inmarshes, at bottom the of lakes, and digestive inthe of tracts environments. The archaea that produce methane gas are obligate anaerobes. oxygen. As you have learned, archaea are prokaryotes that can live inextreme present environment in the or not. of This type a is called leprosy. There are prokaryotes also that oxygen whether can survive is familiar pathogens, such that as those tuberculosis cause diseases and the own.their organisms release nutrients from plants that animals are unable to digest on environment. Organisms that oxygen need environment intheir are called that cannot live presence inthe of oxygen are obligate called anaerobes. An

contain as many as 5 billion bacterial cells from up to 10,000 types of bacteria. found living inside rocks, in deserts, and in polar ice caps. One gram of soil may habitatevery including on Earth, air the we breathe. Prokaryotes have been community ofpart every inhabit. they tiny These organisms live injust about on, above, and under Earth’s and surface. archaea Bacteria are an important M MAI C karyotes.

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9 ) types of) types and bacteria more than 10 Bacteria and archaea are both single-celled single-celled both are archaea and Bacteria (AHB-lih-giht AIR-ohbz). This group includes several (AHB-lih-giht AN-uh-rohb) is poisoned actually by (FAK-uhl-tay-tihv AIR-ohb).

30 E individual prokaryotic cells art Chapter 18:Viruses andProkaryotes figure 4.1. figure h. These micro- These

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cilli magnifications: SEMs; (colored examples are shown at right. named after these shapes.Some and spheres. Manybacteria are shapes ofbac chaeta FIGURE section. using information from this compare bacteria andarchaea Create aVenn diagram to T and Bacteria. have names,Archaea thesame their kingdoms and their domains separate domainsaswell. Both are inseparate kingdoms andin of Life that archaea andbacteria Recall from thechapter TheTree C AKI lassi Unit 6:Clas CO bacteria R magnification unknown; unknown; magnification E N NNE 5000 I D A G G 4.2 f N ica C 3 O

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the threethe most common forms ofare bacteria shown in have and walls cell plasma membranes. Archaea come inmany shapes, while example, archaea both and are bacteria organisms small, single-celled that Even under microscope, the archaea For similar to bacteria. very look Comparisons Structural genetic and biochemical differences. and archaea Bacteria (212°F). have many similarities but structural important Some archaea are even able to grow at temperatures greater than 100°C domains, many while archaea are found inEarth’s extreme environments. prokaryotes. Domain is more the Bacteria diverse and widespread of two the Members of domain and domain Bacteria Archaea comprise of all Earth’s

structurally differentstructurally from of flagella the eukaryotes. are different structurally from each other. In addition, are flagella their both entire cell. Although similar inappearance, ofand flagella the bacteria archaea at one end of an organism, or may they have different arrangements over the prokaryotes are attached to plasma the membrane and may They wall. cell be whiplike structure outside of that acell for is used movement. of The flagella surfaces and to other prokaryotes. Atypical prokaryote is shown in shorter, and often more numerous Pili thanhelp flagella. prokaryotes stick to plasmids. A form of acircle and is surrounded by cytoplasm. Prokaryotes may have also nucleus containing double-stranded DNA. Instead, DNA their is inthe are cocci. called Spiral-shaped are spirilla bacteria called or spirochetes, and spherical bacteria often upon named shapes. based their are bacilli. Rod-shapedbacteria called

move by gliding or using A flagella. separately from prokaryote’s the main chromosome. MAI Lactobacilli: Man Pro Mos N ID karyotes do not have any membrane-bound organelles, such as a t prokaryotes can move on own. their Many and bacteria archaea y prokaryotes contain also pili that structures called are thinner, E A rod-shaped

plasmid is a small piece is asmall of genetic material that can replicate 8c Spirochaeta: flagellum

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(l), (r) ©CNRI/Photo Researchers, Inc. bacteria? bacteria? and archaea between differences two are What te Contrast important molecularimportant differences. Archae T FIGURE his diagram shows thetypical structure ofaprokaryote. this difference,this as shown in are often into classified one of two groups on based is an important characteristic ofBacteria bacteria. cuhn) in their cell walls, which archaea do not. polymer called peptidoglycan (pehp-tih-doh-GLY- type of organism on Earth, and bacteria have a archaea contain lipids that are not found in any other different from those of bacteria. The membranes of ple, archaea cell walls and membranes are chemically with eukaryotes as they do with bacteria. For exam- Molecular evidence suggests that archaea have at least as much in common ties in function and appearance, bacteria and archaea are not closely related. differences between bacteria and archaea became clear. Despite their similari- It was not until molecular analysis techniques were available that the many Comparisons Molecular by to medicine treat used infection. bacterial differences, wall cell archaea are often not affected todoctor of chooses fight infection. their Because sometimes helps of determine type medicine the a anddiagnosing it diseases, infectious bacterial groups apart. The Gram stain is important for aGram called stain tomethod tell is two used the rm that you may still find in some books and articles. articles. and books some in find you may still that rm plasmid The a a andbacteria look very similar, although they have cell wall

4.3 Archaea were first named archaebacteria, a archaebacteria, named were first Archaea mount of peptidoglycan walls cell intheir chromosome p 8c rok aryote Structure aryote membrane plasma FIGURE pili 4.4 . Astaining flagellum wall cell or gram negative. peptidoglycan, that is present. The result is either gram positive of bacteria. This stain identifies the amount of a polymer, called A staining technique called a Gram stain is used to identify types F and stain red. a thinlayer ofpeptidoglycan Gram-negative bacteria have GRAM NEGATIVE membrane outer igure 4.4 igure

gr am (LMs; gram-negative 2,500 gram-negative (LMs;

s t ai peptidoglycan membrane plasma n i n g GRAM POSITIVE and stain purple. a thicker peptidoglycan layer Gram-positive bacteria have Chapter 18:Viruses andProkaryotes 3 ;

gram-positive 550 gram-positive 3 wall cell )

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MAIN IDEA Bacteria have various strategies for survival. The strategies that prokaryotes use to survive and to transfer genes have made them very successful at adapting quickly to almost any habitat. Gene Exchange in Prokaryotes Prokaryotes reproduce by a type of cell division called binary fission, which means “division in half.” While the chromosome copies itself, the cell grows. When the cell has about doubled in size, its plasma membrane grows inward and divides the cell into two equal-sized daughter cells. Each daughter cell will contain a complete copy of the parent cell’s genes.

Although prokaryotes reproduce VISUAL VOCAB asexually, they are still able to exchange In conjugation, genetic material genetic material in several ways. In one transfers between prokaryotes, pro- process, called conjugation (kahn-juh- ducing genetic variation. A conjugation GAY-shuhn), prokaryotes can exchange bridge forms from the donor cell to a parts of their chromosomes through a recipient cell. hollow bridge of pili formed to connect conjugation bridge two or more cells. Surviving Harsh Conditions VIRTUAL Lab During conditions unfavorable for HMDScience.com survival, some bacteria can produce an GO ONLINE endospore, a specialized cell with a thick, TEM; magnification 60003 Testing Antibacterial Agents protective 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 conditions such as drying out, temperature change, and disinfectants. Endospores can last for centuries. Some have even been found in Egyptian mummies! Connect Why are disinfectants alone not enough to kill all types of bacteria?

Self-check Online ©Dr. L. Caro/Photo Inc. L. Researchers, ©Dr. HMDScience.com 18.4 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. What are the three most common 4. Infer Scientists estimate that only Health shapes of bacteria? 1 percent of prokaryotes can be 6. Bacteria in your mouth 2. Why are bacteria and archaea grown in the lab. What does this convert foods containing classified into different domains? suggest about our knowledge of sugar and starch into acids 8c bacteria and archaea? that can then cause cavities in your teeth. These bacteria will 3. Prokaryotes will take up foreign DNA. 5. Synthesize Prokaryotes multiply by be present even if you brush How is this characteristic used in binary fission, which simply divides a your teeth, floss, or use genetic engineering? cell in two. Why are mutations and conjugation important for natural mouthwash. So why are these selection in prokaryotes? hygiene habits so important?

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©Dr. Gary Gaugler/Photo Researchers, Inc. plays initsenvironment. is aspecificrole anorganism of two ormore species.Aniche symbiosis istheclose association Interactions inEcosystems that Recall from thechapter Ecolo VOCABULARY organisms andecosystems and disrupting thehealth ofboth microorganisms inboth maintaining CO NNE 11Csummarizetherole of g 18.5 C y T

T O 11C Beneficial Roles ofProkaryotes or other animals. other Prokaryotes provide and to humans nutrients the rightkindofbacteria! of bacteria. Eating food produced by bacteria isnot dangerous, aslong asthey are cheese, sour cream, andbutterare justafew products that are made withthehelp safe infood, andactually provide ataste ortexture that manypeople enjoy. Swiss poisoning caused by bacteria can beaserious problem. However, some bacteria are People usually thinkbacteria inoronfood are harmful,anditistruethat food Your to World Connect Ke are helpful to us? helpful are Summarize

y ganisms and ecosystems. and ganisms FIGURE 5.1, FIGURE Prokaryotes, such shown as bacteria the in tion by prokaryotes to produce flavors. their cheeses. Pickles, soy sauce, sauerkraut, and on vinegar depend fermenta- also break down, many products day, people dairy eat every such as yogurtand humans enjoy are fermented help by Bacteria ferment, bacteria. or chemically otes inother ways as well. Many that foods stable pHand temperature. and with food ahome bacteria the with a Inbacteria. turn, host the animal provides by disease-causing filled be might otherwise away microbes harmful by niches filling that vitamins and other compounds, and keep getting a place to live. make also They hostthe animal and break down while food relationship, or mutualistic symbiosis, with Prokaryoteshealth. have abeneficial otes is important inour bodies for our systems. community Abalanced of prokary- MAI MAI C Prokaryotes Prokaryotes o Huma N n N ID c ID e

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QUICKLAB observing Examining Bacteria in Yogurt Some types of bacteria can ferment milk, producing lactic acid in the process. Yogurt is a product of fermentation. It is acidic and stays fresh longer than milk, and it is also digested more easily. In this exercise, you will prepare a microscope slide of yogurt. Problem What types of bacteria can you observe in yogurt? Procedure 1. Using a toothpick, place a dab of yogurt on a microscope slide. Caution: Do not eat in Materials the laboratory. • toothpick 2. Mix the yogurt in a drop of water and carefully • dab of plain yogurt add a coverslip. • microscope slide 3. Examine the slide with a compound microscope. • drop of water • coverslip 4. Record your observations by drawing a picture • microscope of what you see through the microscope. Analyze and Conclude 1. Identify Recall the terms bacillus, coccus, and spirilla from the previous section. Which type or types of bacteria did you observe in your slides? 2. Analyze Many people do not produce lactase, which is an enzyme that breaks down the milk sugar lactose. As a result, lactose-intolerant people have trouble digesting dairy products. Why might they have fewer problems eating yogurt?

Main Idea 11C Prokaryotes play important roles in ecosystems. Biology IDEO V CLIP Even though you can’t easily see them, prokaryotes play important roles in HMDScience.com every ecosystem they occupy. Some, such as , produce oxygen

GO ONLINE through photosynthesis. Others help recycle carbon, nitrogen, hydrogen, and Role of Bacteria sulfur through the ecosystem. The absence of prokaryotes in the environment can disrupt an ecosystem, since other organisms rely on them for survival. Photosynthesizing prokaryotes include purple and green photosynthetic bacteria and cyanobacteria. Whereas purple and green bacteria use light to make carbohydrates, they do not produce oxygen. Cyanobacteria, however, are similar to plants in how they produce oxygen as a byproduct of photosyn- thesis. Cyanobacteria are named for their greenish blue (cyan) color. Recall that cyanobacteria played an important part on early Earth, supporting the life forms we are familiar with today. Fossil evidence suggests there was very little oxygen on Earth prior to the appearance of cyanobacteria. Some colonies of photosynthesizing cyanobacteria, as well as other bacte- ria, are also able to fix nitrogen. Although much of the atmosphere is made up

of nitrogen gas (N2), this is not in a form that plants or animals can use to make amino acids or proteins.

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(tr), (c) ©Dr. Jeremy Burgess/Photo Researchers, Inc. ov Apply 18.5 2. 1. Re roots, as shown in live plant’s inthe nodules,rounded small lumps that form the istic relationship with nitrogen-fixing bacteria These bacteria. plants including and beans, clover, alfalfa, peas, have amutual- others live along with other organisms. a group Legumes, of arcticthe tundra. nitrogen to ecosystems ranging from grasslands and forests to compounds that plants can then use. Prokaryotes supply usable cannot are biodegraded of be types plastics. certain to break down amaterial. Some of only the materials made by humans that When you hear term biodegradable, the it often refers to ability the of bacteria poisons. Therefore, play they an important role inrecycling and composting. grow.bacteria accidents. Workers spray oil-polluted that with beaches afertilizer helps the digest oil, which is helpful for cleaning up oil spills and other industrial things to break down pollutants. For example, ofcan some types bacteria (by-oh-rih-mee-dee-AY-shuhn), aprocess that microbes uses and other living at shelter to the bacteria. to produce ammonia. In return, the plant supplies food and trapped soil. inthe combine They nitrogen the with hydrogen nitrogen to plant the by capturing nitrogen gas from air the environment.the One important of use prokaryotes is in er the contaminated area. Why might they do this? do they Why might area. contaminated the er

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Biology VIDEO Web BIOLOGY CLIP Antibiotics in Agriculture What Would You Prescribe? Role of Bacteria Explore Explore links between Review patients’ symptoms and the variety of roles that antibiotic resistance and diagnoses, and then determine if an bacteria play in different antibiotics used in antibiotic should be used to treat environments. agriculture to keep the patients. livestock healthy. @Corbis

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y throughout body. the A cells or by making poisons, or toxins, that by to carried sites can blood be can cause illness to ahost intwo basic ways: by invading tissues and attacking organism’s homeostasis, or stability the of its internal environment. inplants causeSome disease bacteria and animals by disrupting host the in enzymes that cause swelling. That swelling, inturn, damages host’s the lungs. problems. In of case the TB, host the responds to infection the by releasing invasion. The host’s reaction to an invasion by may bacteria itself cause serious multiplybacteria lungs, inthe white cells that killing blood respond to the host’s tissues, and using tissues the for nutrients. Mycobacterium tuberculosis defeat a potential TB infection, especially if there are not many bacteria present. hostthe becomes aware of pathogen’s the presence. Most healthy people can that its immune system defeats. It host’s is the when immune system fails that pathogen inan Ahost infectious disease. is not usually aware of pathogens refrigerated, can multiply bacteria and produce alarge amount of toxin. were contaminated afterwere they cooked. If contaminated is not food common source of poisoning food by S.aureus, however, is from that foods high temperatures cannot destroy a toxin produced by transfer can result in serious food poisoning, known as staph poisoning. Even when food handlers don’t wash their hands after they blow their nose. This S. aureus, MAI d treat disease. disease. treat d MAI C Bacteria Antibiotics Some figure 6.1, figure o TB is ago The di Bac N n N ID c ID teria, such as ept

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MAIN IDEA 7F, 11C Bacteria can evolve resistance Figure 6.4 antibiotic resistance A bacterium carries to antibiotics. genes for antibiotic resistance on a plasmid. Although antibiotics should certainly be used when needed, the inappropriate and incomplete use of antibiotics has A copy of the plasmid is trans- produced a serious public health issue—multidrug-resistant ferred through conjugation. bacteria. Resistance occurs as a result of natural selection, as individuals who are more resistant are more likely to survive and reproduce. This has led to the evolution of multidrug- Resistance is quickly resistant strains of “superbugs” that are almost impossible to spread through many bacteria. treat. As you can see in FIGURE 6.4, bacteria can acquire genes for resistance through plasmid exchange. This has happened with many bacteria treated with a wide range of commonly used antibiotics. This problem has arisen due to various factors. Overuse The potential problem with antibiotics is that they may create a selective pressure that favors the very bacteria they are intended to destroy. Using antibiotics when bacteria are not causing an illness may make some bacteria resistant. Underuse Failure to take the entire course of antibiotics prescribed for a Web bacterial infection is one of the main factors leading to drug resistance. If your HMDScience.com doctor prescribed a ten-day course of an antibiotic, you must finish the entire GO ONLINE prescription. Otherwise, you may not have destroyed all of the bacteria—only the weakest ones. Antibiotics in Agriculture Misuse A large portion of the antibiotics distributed in the United States are fed to livestock. Antibiotics are often misused in agriculture to increase the animals’ rate of growth. However, when antibiotics are added to the food of healthy animals, bacteria within the food—including pathogens—can become resistant to multiple antibiotics. Connect How can you use “superbugs” as an example of natural selection? 7f

Self-check Online HMDScience.com 18.6 Formative Assessment GO ONLINE Reviewing Main Ideas Critical thinking CONNECT TO 1. What are two ways in which bacteria 4. Apply Why are antibiotics not Ecology can cause disease? 11c effective against viruses? 6. Pesticide resistance occurs in 2. How can antibiotics stop bacterial 5. Synthesize Evolution is often much the same way as infections? thought of as taking thousands, or antibiotic resistance. How could we apply what we have 3. What is antibiotic resistance, and how even millions, of years to occur. learned about antibiotic does it occur? 7f What are two reasons that antibiotic resistance has been able to evolve in resistance to how pesticides bacteria so quickly? 7f are used in the environment?

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CHAPTER 18 G N I D A E R

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pollution digestionpollution fights bact The virus ofbact do these meanings relate to the term to live.” The prefixes an epidemic. “people.” Explain how these meanings relate to epi-, whichmeans “upon,” anddemos , whichmeans The term epidemic host andvira meaning, explainmeaning, how itrelates to what conjugation is. conjugare, whichmeans “to jointogether.” Usingthis The term c prot to flagellum. which means “whip. The termcomes flagellum from theLatin word, flagrum

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tion important? tion important? antibiotics whenever possible. Whyisthisrecommenda- Recently th The success of prokaryotes is due to special characteristics helps prokaryotes survive changing environments. perform conjugation. Explain how each of these abilities tions, duringtheirphysic Children across the United States get “shots,” orinjec- shots are andwhythey are recommended for all children. organisms, andwhichtraits donot? living things. Whichoftheirtr Viruses, viroids, andprionsare not considered to be viruses infect bacterial cells? Explain. al virushasanenvelopeThe flu withsurface proteins that engineering? between bacteria anddisease? health andsurvival. their own. Ho Prokaryotes have to theability carry genes other than pre Doctors recommend washing handsbefore eating to ecosystems. Summarizetwo ofthese roles. arra Due to to theirunique ability break down anenormous on bac It surprises most people to learn that theirlives depend infec Explain thedifferences between thetwo ways viruses low itto infect itshost cells. What structures help ey have, such as the ability to form endospores and vent thespread ofdisease. What isthe connection y ofsubstances, prokaryotes play critical roles in t theirhost cells. HMDScience.com Interact teria. Describe three roles bacteria play inhuman , doctors have beenadvised to limittheuse of

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I antibiotic toxin bioremediation endospore conjugation N i ve Review I DEAS 7f al exams. Explain what these 11 Chapter 18: Viruses andProkaryotes Chapter 18: C 4 aits resemble living C 11 C 4c 4 C 11 C

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Critical Thinking 21. Apply Many bacteria cause food spoilage because they Analyzing Data Choose Data Representation have dietary needs similar to humans. However, some Use the hypothetical data below to answer the next bacteria consume chemicals such as heavy metals, sulfur, questions. petroleum, and mercury. How are these bacteria being 11C used to help humans? Type of bacteria and length 22. Compare and Contrast In a lysogenic infection, viral Type of bacteria Average length (nm) genes can become a part of the host’s cell. In a lytic infection, the host cell is destroyed. What might be the Streptococcus 500 benefit of each type of infection to the virus? 4C Staphylococcus 900 23. Infer New viruses may quickly kill their host after Vibrio 2600 infection, but after many generations viruses tend to weaken and cause fewer deaths. Why might it be a Aquaspirillum 2800 disadvantage for a virus to quickly kill its host? 4C 24. Synthesize Endospore-forming bacteria include those Replication time of streptococcus that cause the diseases tetanus, botulism, and anthrax. Time (min) Number of streptococcus cells Endospores themselves, however, do not cause illness and cannot reproduce. Why, then, are endospores such 0 1 a concern to the food and healthcare industries? 11C 28 2 Interpreting Visuals 56 4 Use the diagram below to answer the next three 84 8 questions. The bacteriophage attaches The host bacterium and injects its DNA into a host 28. Connect For each of the tables above, identify whether breaks apart, or lyses. bacterium. the data are continuous or discrete. Explain. Bacteriophages are able to infect new host cells. 29. Calculate Assuming that nutrients are unlimited, how many Streptococcus cells will there be after 112 minutes? Explain. host bacterium

Making Connections The viral DNA 30. Writing a Pamphlet Scientists agree that a form of the forms a circle. avian flu virus has the potential to cause a worldwide flu epidemic. This type of virus is known to mutate easily and adapt quickly to host changes. Imagine you are a representative from the Centers for Disease Control The viral DNA directs the host cell to and are writing a pamphlet to educate citizens about produce new viral parts. The parts the virus and how it actually causes infection. Using assemble into new bacteriophages. your knowledge of cells and viruses, make a detailed pamphlet that the general public could understand. 25. Apply What type of viral infection is shown above? 4C Explain your answer. 4C 31. Synthesize The bacteria in the esophagus shown on the 26. Apply Why is it necessary for the viral genes to enter chapter opener are one of the many types of symbiotic the host cell? 4C prokaryotes living within our bodies. How might these types of mutualistic relationships have arisen? Consider 27. Analyze How would the way that the virion enters the natural selection in your answer. host cell change if the virus were a type that infected 11C animals, and the host cell were eukaryotic rather than prokaryotic? 4C

552 Unit 6: Classification and Diversity Biology End-of-Course Exam Practice

Record your answers on a separate piece of paper. 11C, 12E MULTIPLE CHOICE 4 Some scientists think that measures of an ecosystem’s health—such as usable nitrogen levels in 2G, 11C the soil—may become more variable as the diversity 1 of organisms on Earth declines. This is because usable soil nitrogen depends on a variety of — The Eects of Antibiotics on Infected Mice A animals that return nitrogen to the soil Antibiotic ABC through respiration Infected mice tested 30 15 15 B animals that return nitrogen to the soil after 83% 25% 100% they die C bacteria and other decomposers that fix Scientists are testing three antibiotics—A, B, and nitrogen into a usable form C—on 60 mice with bacterial infections. Based D plants, which produce nitrogen as a byproduct on the table above, what is the most likely reason of photosynthesis why the scientists concluded that they needed to do more testing on antibiotic C? 4C A They did not test the side effects of antibiotic C. 5 The main reason that viruses are not considered B Antibiotic C worked better than A and B. to be living things is because — C Antibiotic C had 100% effectiveness. A they are not affected by antibiotics D The sample size was too small. B they cannot reproduce on their own C they do not contain a nucleus 11C D they do not contain any nucleic acids 2 Impetigo is a highly contagious skin infection caused by staph or strep bacteria that are normally THINK THROUGH THE QUESTION found on the skin, where they are harmless. This All of these answer choices correctly describe infection is most likely to occur when — viruses, so do not be tricked! Look at each answer choice and try to think of a living organism that fits A the bacteria gain access to the body through the characteristic described, making that answer scraped skin choice wrong. B an uninfected person comes in contact with an infected person C the infected person did not receive regularly 4A, 4C, 8C scheduled vaccinations 6

D the bacteria release endospores on the surface ?? of the skin reproduces has doesn’t chlorophyll 4C asexually have DNA 3 Hepatitis B is a viral disease that attacks cells in nucleus the liver. When should a person receive a membrane-bound vaccination against hepatitis B? organelles A before being exposed to the virus Which of the following can be described by the B as soon as viral symptoms begin to appear concept map above? C after being diagnosed with the disease A an earthworm’s muscle cell D never; the overuse of vaccines has lead to viral B an oak tree’s leaf cell resistance C a bacterium D a human immunodeficiency virus (HIV)

Chapter 18: Viruses and Prokaryotes 553