Table of Contents pages iiiUnit 1: What is Biology?Unit 2: EcologyUnit 3: The Life of a CellUnit 4: GeneticsUnit 5: Change Through TimeUnit 6: Viruses, Bacteria, Protists, and FungiUnit 7: PlantsUnit 8: InvertebratesUnit 9: VertebratesUnit 10: The Human Body

Table of Contents pages vii-xiiiUnit 1: What is Biology? Chapter 1: Biology: The Study of LifeUnit 2: Ecology Chapter 2: Principles of Ecology Chapter 3: Communities and Biomes Chapter 4: Population Biology Chapter 5: Biological Diversity and ConservationUnit 3: The Life of a Cell Chapter 6: The Chemistry of Life Chapter 7: A View of the Cell Chapter 8: Cellular Transport and the Cell Cycle Chapter 9: Energy in a Cell

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Unit 4: Genetics Chapter 10: Mendel and Meiosis Chapter 11: DNA and Genes Chapter 12: Patterns of Heredity and Human Genetics Chapter 13: Genetic TechnologyUnit 5: Change Through Time Chapter 14: The History of Life Chapter 15: The Theory of Evolution Chapter 16: Primate Evolution Chapter 17: Organizing Lifes Diversity

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Unit 6: Viruses, Bacteria, Protists, and Fungi Chapter 18: Viruses and Bacteria Chapter 19: Protists Chapter 20: Fungi Unit 7: Plants Chapter 21: What Is a Plant? Chapter 22: The Diversity of Plants Chapter 23: Plant Structure and Function Chapter 24: Reproduction in Plants

Table of Contents pages vii-xiiiUnit 8: Invertebrates Chapter 25: What Is an Animal? Chapter 26: Sponges, Cnidarians, Flatworms, and Roundworms Chapter 27: Mollusks and Segmented Worms Chapter 28: Arthropods Chapter 29: Echinoderms and Invertebrate Chordates

Table of Contents pages vii-xiiiUnit 9: Vertebrates Chapter 30: Fishes and Amphibians Chapter 31: Reptiles and Birds Chapter 32: Mammals Chapter 33: Animal BehaviorUnit 10: The Human Body Chapter 34: Protection, Support, and Locomotion Chapter 35: The Digestive and Endocrine Systems Chapter 36: The Nervous System Chapter 37: Respiration, Circulation, and Excretion Chapter 38: Reproduction and Development Chapter 39: Immunity from Disease

Unit Overview pages 472-473Viruses, Bacteria, Protists, and FungiViruses and BacteriaProtistsFungi

Chapter Contents page ixChapter 18 Viruses and Bacteria 18.1: Viruses 18.1: Section Check 18.2: Archaebacteria and Eubacteria18.2: Section CheckChapter 18 SummaryChapter 18 Assessment

Chapter Intro-page 474What Youll LearnYou will identify the structures and characteristics of viruses and bacteria.You will explain how viruses and bacteria reproduce.You will recognize the medical and economic importance of viruses and bacteria.

18.1 Section Objectives page 475Identify the different kinds of viruses and their structures.Section Objectives: Compare and contrast the replication cycles of viruses.

Section 18.1 Summary pages 475-483Youve probably had the fluinfluenzaat some time during your life.Viruses are nonliving particles composed of nucleic acids enclosed in a protein coat and are smaller than the smallest bacterium.What is a virus?Nonliving particles called viruses cause influenza.

Section 18.1 Summary pages 475-483Most biologists consider viruses to be nonliving because they dont exhibit all the criteria for life.They dont carry out respiration, grow, or develop. All viruses can do is replicatemake copies of themselvesand they cant even do that without the help of living cells.What is a virus?A cell in which a virus replicates is called the host cell.

Section 18.1 Summary pages 475-483Viruses, such as rabies viruses and polioviruses, were named after the diseases they cause.Other viruses were named for the organ or tissue they infect.What is a virus? They do not get Latin names because they are nonliving.

Section 18.1 Summary pages 475-483What is a virus?Today, most viruses are given a genus name ending in the word virus and a species name.However, sometimes scientists use code numbers to distinguish among similar viruses that infect the same host.A virus that infects a bacterium is called a bacteriophage (bak TIHR ee uh fayj), or phage for short.

Section 18.1 Summary pages 475-483Viral StructureA virus has an inner core of nucleic acid, either RNA or DNA, and an outer protein coat called a capsid.CapsidNucleic acidEnvelope

Section 18.1 Summary pages 475-483Viral StructureSome relatively large viruses, such as human flu viruses, may have an additional layer, called an envelope, surrounding their capsids.CapsidNucleic acidEnvelope

Section 18.1 Summary pages 475-483Viral StructureEnvelopes are composed primarily of the same materials found in the plasma membranes of all cells.CapsidNucleic acidEnvelope

Section 18.1 Summary pages 475-483Viral nucleic acid is either DNA or RNA and contains instructions ONLY for making copies of the virus.Some viruses have only four genes, while others have hundreds.Nucleic acidCapsidViral Structure

Section 18.1 Summary pages 475-483The tobacco mosaic virus has a long, narrow helical shape.Nucleic acidCapsidViral Structure

Section 18.1 Summary pages 475-483Viral StructureThe arrangement of proteins in the capsid of a virus determines the viruss shape.Nucleic acidCapsidPolyhedral viruses resemble small crystals.

Section 18.1 Summary pages 475-483Viral StructureThe protein arrangement also plays a role in determining what cell can be infected and how the virus infects the cell.Nucleic acidCapsid

Section 18.1 Summary pages 475-483Attachment to a host cellBefore a virus can replicate, it must enter a host cell.A virus recognizes and attaches to a host cell when one of its proteins interlocks with a molecular shape that is the receptor site on the host cells plasma membrane.

Section 18.1 Summary pages 475-483Attachment to a host cellA protein in the tail fibers of the bacteriophage T4 recognizes and attaches the T4 to its bacterial host cell.CapsidNucleic acidTailTail fiber

Section 18.1 Summary pages 475-483Attachment to a host cellIn other viruses, the attachment protein is in the capsid or in the envelope.CapsidNucleic acidTailTail fiber

Section 18.1 Summary pages 475-483Attachment is a specific processEach virus has a specifically shaped attachment protein. Therefore, each virus can usually attach to only a few kinds of cells.In general, viruses are species specific, and some also are cell-type specific. For example, polio viruses normally infect only intestinal and nerve cells.

Section 18.1 Summary pages 475-483Attachment is a specific processThe species specific characteristic of viruses is significant for controlling the spread of viral diseases.

Section 18.1 Summary pages 475-483Viral Replication CyclesOnce attached to the plasma membrane of the host cell, the virus enters the cell and takes over its metabolism.Only then can the virus replicate.Viruses have two ways of getting into host cells.

Section 18.1 Summary pages 475-483Viral Replication CyclesThe virus may inject its nucleic acid into the host cell like a syringe injects a vaccine into your arm.The capsid of the virus stays attached to the outside of the host cell.An enveloped virus enters a host cell in a different way.

Section 18.1 Summary pages 475-483Viral Replication CyclesAfter attachment by these enveloped viruses, the plasma membrane of the host cell surrounds the virus and produces a virus-filled vacuole inside the host cells cytoplasm.Then, the virus bursts out of the vacuole and releases its nucleic acid into the cell.

Section 18.1 Summary pages 475-483Lytic cycleOnce inside the host cell, a viruss genes are expressed and the substances that are produced take over the host cells genetic material.The viral genes alter the host cell to make new viruses.

Section 18.1 Summary pages 475-483Nucleic acidBacterial host cellBacteriophageBacterial DNAB. EntryThe bacteriophage injects its nucleic acid into the bacterial cell.A. AttachmentC. ReplicationD. AssemblyE. Lysis and ReleaseThe hosts metabolic machinery makes viral nucleic acid and proteins. New virus particles are assembled. The host cell breaks open and releases new virus particles. Lytic cycle

Section 18.1 Summary pages 475-483Lytic cycleThe host cell uses its own enzymes, raw materials, and energy to make copies of viral genes that along with viral proteins are assembled into new viruses, which burst from the host cell, killing it.

Section 18.1 Summary pages 475-483Lytic cycleThe new viruses can then infect and kill other host cells. This process is called a lytic (LIH tik) cycle.Click image to play movie

Section 18.1 Summary pages 475-483Lysogenic cycleNot all viruses kill the cells they infect.Some viruses go through a lysogenic cycle, a replication cycle in which the viruss nucleic acid is integrated into the host cells chromosome.Click image to play movie

Section 18.1 Summary pages 475-483Lysogenic cycleA lysogenic cycle begins in the same way as a lytic cycle.However, in a lysogenic cycle, instead of immediately taking over the hosts genetic material, the viral DNA is integrated into the host cells chromosome.

Section 18.1 Summary pages 475-483Lysogenic cycle

Section 18.1 Summary pages 475-483Disease symptoms of provirusesMany disease-causing viruses have lysogenic cycles. However, when in the lysogenic cycle, there are no symptoms of the disease. Its like a dormant stage.Three examples of these viruses are herpes simplex I (causes cold sores), herpes simplex II that causes genital herpes, and the hepatitis B virus that causes hepatitis B.

Section 18.1 Summary pages 475-483Disease symptoms of provirusesAnother lysogenic virus is the one that causes chicken pox. When a cold sore is present, the virus is in the lytic cycle. When the cold sore disappears, the virus is in the lysogenic cycle.

Section 18.1 Summary pages 475-483Disease symptoms of provirusesHaving chicken pox, which usually occurs before age ten, gives lifelong protection from another infection by the virus. However, some chicken pox viruses may remain as proviruses in some of your bodys nerve cells.

Section 18.1 Summary pages 475-483Disease symptoms of provirusesLater in your life, these proviruses may enter a lytic cycle and cause a disease called shinglesa painful infection of some nerve cells.

Section 18.1 Summary pages 475-483Release of virusesEither lysis, the bursting of a cell, or exocytosis, the active transport process by which materials are expelled from a cell, release new viruses from the host cell.

Section 18.1 Summary pages 475-483Release of virusesIn exocytosis, a newly produced virus approaches the inner surface of the host cells plasma membrane.The plasma membrane surrounds the virus, enclosing it in a vacuole that then fuses with the host cells plasma membrane.Then, the viruses are released to the outside.

Section 18.1 Summary pages 475-483Once inside a human host, HIV infects white blood cells.Newly made viruses are released into the blood stream by exocytosis and infect other white blood cells.Normal white blood cellsHIV: An infection of white blood cells

Section 18.1 Summary pages 475-483HIV: An infection of white blood cellsInfected host cells still function normally because the viral genetic material is a provirus that produces only a small number of new viruses at a time.Because the infected cells are still able to function normally, an infected person may not appear sick, but they can still transmit the virus in their body fluids.

Section 18.1 Summary pages 475-483HIV: An infection of white blood cellsMost people with an HIV infection eventually get AIDS because, over time, more white blood cells are infected and produce new viruses.Because white blood cells are part of a bodys disease-fighting system, their destruction interferes with the bodys ability to protect itself from organisms that cause disease, a symptom of AIDS.

Section 18.1 Summary pages 475-483RetrovirusesMany viruses, such as the human immunodeficiency virus (HIV) that causes the disease AIDS, are RNA virusesRNA being their only nucleic acid.HIV virus

Section 18.1 Summary pages 475-483Retroviruses

Section 18.1 Summary pages 475-483Cancer and VirusesSome viruses have been linked to certain cancers in humans and animals (Human papilloma virus HPV- cervical cancer).These viruses disrupt the normal growth and division of cells in a host, causing abnormal growth and creating tumors.

Section 18.1 Summary pages 475-483Plant virusesThe first virus to be identified was a plant virus, called tobacco mosaic virus, that causes disease in tobacco plants.Tobacco mosaic virus causes yellow spots on tobacco leaves, making them unmarketable.

Section 18.1 Summary pages 475-483Plant virusesViruses cause as many as 1000 plant diseases and are named according to their host plant.Viruses can cause stunted growth and yield losses in their host plants.

Section 18.1 Summary pages 475-483Plant virusesPlant viruses require wounds or insect bites to enter and infect a host, and do not use surface recognition.They do not undergo lytic or lysogenic phases.

Section 18.1 Summary pages 475-483Plant virusesNot all viral plant diseases are fatal or even harmful.Some mosaic viruses cause striking patterns of color in the flowers of plants.Rembrandt tulips

Section 18.1 Summary pages 475-483Prions and viroidsResearchers have recently discovered some particles that behave somewhat like viruses and cause infectious diseases.Prions are composed of proteins but have no nucleic acid to carry genetic information.

Section 18.1 Summary pages 475-483Prions and viroidsPrions are thought to act by causing other proteins to fold themselves incorrectly, resulting in improper functioning.Prions are responsible for many animal diseases, such as mad cow disease and its human equivalent, Creutzfeldt-Jakob disease, which causes nerve cells in the brain to burst.

Section 18.1 Summary pages 475-483Prions and viroidsViroids are composed of a single circular strand of RNA with no protein coat.Viroids have been shown to cause infectious diseases in several plants.The amount of viroid RNA is much less than the amount found in viruses.

Section 18.1 Summary pages 475-483Origin of VirusesFor replication, viruses need host cells; therefore, scientists suggest that viruses might have originated from their host cells.Some scientists suggest that viruses are nucleic acids that break free from their host cells while maintaining an ability to replicate parasitically within the host cells.

Section 1 CheckQuestion 1Which of the following is NOT a reason that viruses are considered to be nonliving? D. Viruses dont develop.C. Viruses dont grow.B. Viruses dont respire.A. Viruses dont replicate. The answer is A.

Section 1 CheckQuestion 2Which is NOT a component of a virus? D. phageC. DNA B. capsid A. RNA The answer is D.

Section 1 CheckQuestion 3Which of the following is NOT determined by the arrangement of proteins in the capsid of a virus?D. how the virus infects a cell C. whether or not the virus will have an envelope around itB. what cell can be infected by the virus A. shape

Section 1 CheckThe answer is C.

Section 1 CheckQuestion 4What two ways do viruses have of getting into host cells?AnswerThe virus can inject its nucleic acid into the host cell, or attach to the host cells membrane and become surrounded by the membrane and placed in a vacuole. The virus then bursts out of the vacuole and releases its nucleic acid into the cell.

Section 1 CheckQuestion 5In the lytic cycle, after the hosts metabolic machinery makes viral nucleic acid and proteins the next phase is _______.D. attachment C. assemblyB. replicationA. lysis and release

Section 1 CheckThe answer is C. In the assembly phase, the new virus particles are assembled.

Section 2 Objectives page 484Section Objectives Explain the characteristics and adaptations of bacteria. Compare the types of prokaryotes. Evaluate the economic importance of bacteria.

Section 18.2 Summary pages 484-495 Recall that prokaryotes are unicellular organisms that do not have a nucleus or membrane-bound organelles.Diversity of Prokaryotes They are classified in two kingdomsarchaebacteria and eubacteria. Many biochemical differences exist between these two types of prokaryotes.

Section 18.2 Summary pages 484-495 Because they are so different, many scientists propose that archaebacteria and eubacteria arose from a common ancestor several billion years ago.Diversity of Prokaryotes

Section 18.2 Summary pages 484-495 There are three types of archaebacteria that live mainly in extreme habitats where there is usually no free oxygen available.Archaebacteria: The extremists One type of archaebacterium lives in oxygen-free environments and produces methane gas.

Section 18.2 Summary pages 484-495 These methane-producing archaebacteria live in marshes, lake sediments, and the digestive tracts of some mammals, such as cows.Archaebacteria: The extremists

Section 18.2 Summary pages 484-495Archaebacteria: The extremists They also are found at sewage disposal plants, where they play a role in the breakdown of sewage.

Section 18.2 Summary pages 484-495 A second type of archaebacterium lives only in water with high concentrations of salt.Archaebacteria: The extremists Dead Sea

Section 18.2 Summary pages 484-495 A third type lives in the hot, acidic waters of sulfur springs.Archaebacteria: The extremists

Section 18.2 Summary pages 484-495 This type of anaerobic archaebacterium also thrives near cracks deep in the ocean floor, where it is the autotrophic producer for a unique animal communitys food chain.Archaebacteria: The extremists

Section 18.2 Summary pages 484-495 Eubacteria, the other kingdom of prokaryotes, includes those prokaryotes that live in places more hospitable than archaebacteria inhabit and that vary in nutritional needs.Eubacteria: The heterotrophs The heterotrophic eubacteria live almost everywhere and use organic molecules as their food source.

Section 18.2 Summary pages 484-495 Some bacterial heterotrophs are parasites, obtaining their nutrients from living organisms.Eubacteria: The heterotrophs Others are saprophytesorganisms that feed on dead organisms or organic wastes.

Section 18.2 Summary pages 484-495 A second type of eubacterium is the photosynthetic autotroph.Eubacteria: Photosynthetic autotrophs These eubacteria live in places with sunlight because they need light to make the organic molecules that are their food.

Section 18.2 Summary pages 484-495 Cyanobacteria are photosynthetic autotrophs.Eubacteria: Photosynthetic autotrophs Most cyanobacteria are blue-green and some are red or yellow in color. Cyanobacteria

Section 18.2 Summary pages 484-495Eubacteria: Photosynthetic autotrophs Cyanobacteria commonly live in ponds, streams, and moist areas of land. They are composed of chains of independent cells. Cyanobacteria

Section 18.2 Summary pages 484-495 A third type of eubacterium is the chemosynthetic autotroph.Eubacteria: Chemosynthetic autotrophs Unlike the photosynthetic bacteria, the chemosynthetic bacteria do not obtain the energy they need to make food from sunlight.

Section 18.2 Summary pages 484-495Eubacteria: Chemosynthetic autotrophs Instead, they break down and release the energy of inorganic compounds containing sulfur and nitrogen in the process called chemosynthesis.

Section 18.2 Summary pages 484-495What is bacterium? A bacterium consists of a very small cell. Although tiny, a bacterial cell has all the structures necessary to carry out its life functions.

Section 18.2 Summary pages 484-495The structure of bacteria Prokaryotic cells have ribosomes, but their ribosomes are smaller than those of eukaryotes. They also have genes that are located for the most part in a single circular chromosome, rather than in paired chromosomes.

Section 18.2 Summary pages 484-495The structure of bacteria RibosomeCytoplasmChromosomeGelatinlikecapsuleCell WallCell MembraneFlagellum

Section 18.2 Summary pages 484-495A Typical Bacterial Cell A typical bacterium, such as Escherichia coli would have some or all of the structures shown in this diagram of a bacterial cell.CapsuleCell WallChromosomeFlagellumPlasmidPilusPlasma membrane

Section 18.2 Summary pages 484-495The structure of bacteria A bacterial cell remains intact as long as its cell wall is intact. If the cell wall is damaged, water will enter the cell by osmosis, causing the cell to burst. Scientists used a bacteriums need for an intact cell wall to develop a weapon against bacteria that cause disease.

Section 18.2 Summary pages 484-495The structure of bacteria In 1928, Sir Alexander Fleming accidentally discovered penicillin, the first antibiotica substance that destroys bacteriaused in humans.

Section 18.2 Summary pages 484-495The structure of bacteria Later, biologists discovered that penicillin can interfere with the ability of some bacteria to make cell walls. When such bacteria grow in penicillin, holes develop in their cell walls, water enters their cells, and they rupture and die.

Section 18.2 Summary pages 484-495Identifying bacteria One trait that helps categorize bacteria is how they react to Gram stain. Gram staining is a technique that distinguishes two groups of bacteria because the stain reflects a basic difference in the composition of bacterial cell walls.

Section 18.2 Summary pages 484-495 After staining, Gram-positive bacteria are purple and Gram-negative bacteria are pink.Gram-positive bacteriaGram-negative bacteriaIdentifying bacteria

Section 18.2 Summary pages 484-495 Gram-positive bacteria are affected by different antibiotics than those that affect Gram-negative bacteria.Gram-positive bacteriaGram-negative bacteriaIdentifying bacteria

Section 18.2 Summary pages 484-495Identifying bacteria Bacterial cell walls also give bacteria different shapes. Shape is another way to categorize bacteria.

Section 18.2 Summary pages 484-495Identifying bacteria The three most common shapes are spheres, called coccus; rods, called bacillus; and spirals, called spirillum.

Section 18.2 Summary pages 484-495Identifying bacteria In addition to having one of these shapes, bacterial cells often grow in characteristic patterns that provide another way of categorizing them.

Section 18.2 Summary pages 484-495Identifying bacteria Diplois a prefix that refers to a paired arrangement of cell growth. The prefix staphylodescribes an arrangement of cells that resemble grapes. Streptois a prefix that refers to an arrangement of chains of cells.

Section 18.2 Summary pages 484-495Reproduction by binary fission Bacteria reproduce asexually by a process known as binary fission. To reproduce in this way, a bacterium first copies its chromosome. Then the original chromosome and the copy become attached to the cells plasma membrane for a while.

Section 18.2 Summary pages 484-495Reproduction by binary fission The cell grows larger, and eventually the two chromosomes separate and move to opposite ends of the cell.

Section 18.2 Summary pages 484-495Reproduction by binary fission Then, a partition forms between the chromosomes. This partition separates the cell into two similar cells.

Section 18.2 Summary pages 484-495Reproduction by binary fission Because each new cell has either the original or the copy of the chromosome, the resulting cells are genetically identical.

Section 18.2 Summary pages 484-495Reproduction by binary fission Under ideal conditions, some bacteria can reproduce every 20 minutes, producing enormous numbers of bacteria quickly. But bacteria dont always have ideal growing conditions. They run out of nutrients and water, they poison themselves with their own wastes, and predators eat them.

Section 18.2 Summary pages 484-495Sexual reproduction In addition to binary fission, some bacteria have a form of sexual reproduction called conjugation. During conjugation (kahn juh GAY shun), one bacterium transfers all or part of its chromosome to another cell through or on a bridgelike structure called a pilus that connects the two cells.

Section 18.2 Summary pages 484-495Sexual reproduction Conjugation results in a bacterium with a new genetic composition. This bacterium can then undergo binary fission, producing more cells with the same genetic makeup.

Section 18.2 Summary pages 484-495Adaptations in Bacteria Based on fossil evidence, some scientists propose that anaerobic bacteria were probably among the first photosynthetic organisms, producing not only their own food but also oxygen. As the concentration of oxygen increased in Earths atmosphere, some bacteria probably adapted over time to use oxygen for respiration.

Section 18.2 Summary pages 484-495Diversity of metabolism Modern bacteria have diverse types of respiration. Many bacteria require oxygen for respiration. These bacteria are called obligate aerobes. There are other bacteria, called obligate anaerobes, that are killed by oxygen.

Section 18.2 Summary pages 484-495Diversity of metabolism There are still other bacteria that can live either with or without oxygen, releasing the energy in food aerobically by cellular respiration or anaerobically by fermentation.

Section 18.2 Summary pages 484-495A survival mechanism Some bacteria, when faced with unfavorable environmental conditions, produce endospores. An endospore is a tiny structure that contains a bacteriums DNA and a small amount of its cytoplasm, encased by a tough outer covering that resists drying out, temperature extremes, and harsh chemicals.

Section 18.2 Summary pages 484-495A survival mechanism When environmental conditions improve, the endospore germinates, or produces a cell that begins to grow and reproduce. Some endospores have germinated after thousands of years in the resting state. As an endospore, the bacterium rests and does not reproduce.

Section 18.2 Summary pages 484-495A survival mechanism Endospores can survive a temperature of 100C, which is the boiling point of water.

Section 18.2 Summary pages 484-495A survival mechanism To kill endospores, items must be sterilizedheated under high pressure in either a pressure cooker or an autoclave.

Section 18.2 Summary pages 484-495A survival mechanism This is because the endospores of the bacterium called Clostridium botulinum easily get into foods being canned. Canned food must be sterilized and acidified.

Section 18.2 Summary pages 484-495A survival mechanism Bacteria grow in the anaerobic environment of the can and produce a powerful deadly poison, called a toxin, as they grow. If the endospores of C. botulinum get into improperly sterilized canned food, they germinate. This deadly toxin saturates the food and, if eaten, causes the disease called botulism.

Section 18.2 Summary pages 484-495A survival mechanism B. anthracis causes anthrax, a disease that commonly infects cattle and sheep, but can also infect humans. A different bacterium, Bacillus anthracis, lives in the soil. Most human anthrax infections are fairly harmless and occur on the skin as a result of handling animals.

Section 18.2 Summary pages 484-495A survival mechanism This infection is more serious than a skin infection and often fatal. The bacterial spores can become airborne, however, and if inhaled in large amounts, can germinate in a persons lungs, causing an infection.

Section 18.2 Summary pages 484-495The Importance of Bacteria Bacteria help to fertilize fields, to recycle nutrients on Earth, and to produce foods and medicines. Disease-causing bacteria are few compared with the number of harmless and beneficial bacteria on Earth.

Section 18.2 Summary pages 484-495Nitrogen fixation Yet few organisms, including most plants, can directly use nitrogen from the air. All organisms need nitrogen because the element is a component of their proteins, DNA, RNA, and ATP.

Section 18.2 Summary pages 484-495Nitrogen fixation Other bacteria then convert the ammonia into nitrite (NO2) and nitrate (NO3),which plants can use. Several species of bacteria have enzymes that convert N2 into ammonia (NH3) in a process known as nitrogen fixation. Bacteria are the only organisms that can perform these chemical changes.

Section 18.2 Summary pages 484-495Nitrogen fixation Farmers grow legume crops after the harvesting of crops such as corn, which depletes the soil of nitrogen. Some nitrogen-fixing bacteria live symbiotically within the roots of some trees and legumes.

Section 18.2 Summary pages 484-495Recycling of nutrients This food is passed from one heterotroph to the next in food chains and webs. Autotrophic bacteria and also plants and algae, which are at the bottom of the food chains, use the nutrients in the food they make. In the process of making food, many autotrophs replenish the supply of oxygen in the atmosphere.

Section 18.2 Summary pages 484-495Food and medicines Some foods that you eatmellow Swiss cheese, crispy pickles, tangy yogurtwould not exist without bacteria.

Section 18.2 Summary pages 484-495Food and medicines Specific bacteria are used to make different foods, such as vinegar, cheeses, and sauerkraut. Bacteria also inhabit your intestines and produce vitamins and enzymes that help digest food.

Section 18.2 Summary pages 484-495Food and medicines Streptomycin, erythromycin, bacitracin, and neomycin are some of these antibiotics. In addition to food, some bacteria produce important antibiotics that destroy other types of bacteria.

Section 18.2 Summary pages 484-495Bacteria cause disease Bacteria also cause many human diseases. Bacteria cause diseases in plants and animals, causing crops and livestock losses that impact humans indirectly. Disease-causing bacteria can enter human bodies through openings, such as the mouth.

Section 18.2 Summary pages 484-495Bacteria cause disease The growth of the bacteria can interfere with the normal function of body tissue, or it can release a toxin that directly attacks the host. Bacterial diseases harm people in two ways.

Section 18.2 Summary pages 484-495Bacteria cause diseaseDiseases Caused by BacteriaDiseaseTransmissionSymptomsTreatmentStrep throat(Streptococcus)Inhale or ingest throughmouthFever, sore throat,swollen neck glandsAntibioticTuberculosisInhale Fatigue, fever, nightsweats, cough, weight loss, chest painAntibioticTetanusPuncturewoundStiff jaw, musclespasms, paralysisOpen and clean wound,antibiotic; give antitoxinLyme diseaseBite ofinfected tickRash at site of bite,chills, body aches,joint swellingAntibioticDentalcavities (caries)Bacteriain mouthDestruction of toothenamel, toothacheRemove and fill thedestroyed area of toothDiptheriaInhale orclose contactSore throat, fever,heart or breathingfailure Vaccination to prevent, antibiotics

Section 18.2 Summary pages 484-495Bacteria cause disease In the last 100 years, human life expectancy has increased to about 75 years. In the past, bacterial illnesses had a greater effect on human populations than they do now.

Section 18.2 Summary pages 484-495Bacteria cause disease This increase is due to many factors, including better public health systems, improved water and sewage treatment, better nutrition, and better medical care. These improvements, along with antibiotics, have reduced the death rates from bacterial diseases to low levels.

Section 2 Check Which of the following best describes archaebacteria? Question 1D. parasitic heterotrophs C. chemosynthetic autotrophsB. photosynthetic autotrophs A. anaerobic autotrophs The answer is A.

Section 2 Check What part of a bacterial cell is most affected by penicillin? Question 2D. cell wall C. flagellum B. plasmidA. pilus

Section 2 CheckThe answer is D, cell wall.Cell Wall

Section 2 Check Which of the following is not a way to identify bacteria? Question 3D. lack of a plasma membrane C. characteristic growth patterns B. shape A. the way in which their cell walls reflect Gram stain The answer is D.

Section 2 Check Given their rapid reproductive rates, why arent there more bacteria than there actually are? Question 4AnswerBacteria dont always have ideal growing conditions. They run out of nutrients and water, they poison themselves with their own wastes, and predators eat them.

Section 2 Check What is a pilus used for in a bacterium? Question 5

Section 2 CheckA pilus helps a bacterium stick to a surface. It is also a bridge through or on which two bacteria can exchange DNA.CapsuleCell WallChromosomeFlagellumPlasmidPilusPlasma membrane

Chapter Summary 18.1Viruses are nonliving particles that have a nucleic acid core and a protein-containing capsid.Viruses To replicate, a virus must first recognize a host cell, then attach to it, and finally enter the host cell and take over its metabolism.

Chapter Summary 18.1During a lytic cycle, a virus replicates and kills the host cell. In a lysogenic cycle, a viruss DNA is integrated into a chromosome of the host cell, but the host cell does not die.Viruses Retroviruses contain RNA. Reverse transcriptase is an enzyme that helps convert viral RNA to DNA, which is then integrated into the host cells chromosome.

Chapter Summary 18.1Prions and viroids are virus-like particles. Prions are composed of only a protein, while a viroid is a singular strand of RNA.Viruses Viruses probably originated from their host cells.

Chapter Summary 18.2There are two kingdoms of prokaryotes: archaebacteria and eubacteria. Archaebacteria inhabit extreme environments. Eubacteria live almost everywhere else. They probably arose separately from a common ancestor billions of years ago.Archaebacteria and Eubacteria

Chapter Summary 18.2Bacteria are varied. Some are heterotrophs, some are photosynthetic autotrophs, and others are chemosynthetic autotrophs. Bacteria can be obligate aerobes, obligate anaerobes, or both aerobic and anaerobic.Archaebacteria and Eubacteria

Chapter Summary 18.2Archaebacteria and Eubacteria Bacteria usually reproduce by binary fission. Some have a type of sexual reproduction called conjugation. Some bacteria form endospores that enable them to survive when conditions are unfavorable.

Chapter AssessmentQuestion 1With lysogenic viruses, what two phases of the lytic cycle are replaced by the lysogenic cycle?D. attachment and entry C. assembly and lysis and release B. replication and assemble A. entry and replication

The answer is D.LYSOGENIC CYCLELYTIC CYCLEA. Attachment and EntryChapter Assessment

Chapter AssessmentQuestion 2Explain why you can be infected with a virus but may have no symptoms of disease for years after the initial infection.AnswerThe virus enters a lysogenic phase remaining inactive but replicating along with the host cells chromosomes. Eventually, the virus enters a lytic phase where it destroys its host cells and causes symptoms of disease.

Chapter AssessmentQuestion 3What is the difference between lysis and exocytosis with respect to host cells that contain viruses?AnswerLysis, the bursting of the host cell, is caused when viruses break out of it. In exocytosis, the virus is enclosed in a vacuole that then fuses with the host cells plasma membrane. The virus is then released to the outside.

Chapter AssessmentQuestion 4What is the importance of reverse transcriptase to a retrovirus?AnswerThe enzyme reverse transcriptase allows the retrovirus to make DNA from its RNA so the DNA may attach to the chromosomes of the host cell and divide with the host cell.

Chapter AssessmentQuestion 5Particles that are composed of proteins but have no nucleic acid to carry genetic information are _______.D. retroviruses C. viroids B. prionsA. proviruses The answer is B.

Chapter AssessmentDuring ______, a bacterium transfers all or part of its chromosome to another bacterium.D. chemosynthesisC. conjugation B. attachment A. binary fission The answer is C.Question 6

Chapter AssessmentWhat causes botulism? AnswerEndospores of C. botulinum bacteria get into an anaerobic environment like improperly canned food, germinate, and produce a toxin as they grow. This toxin is then ingested by humans and causes poisoning called botulism.Question 7

Chapter AssessmentWhat causes anthrax? Question 8

Endospores of B. anthracis bacteria produce endospores that can become airborne, and if inhaled in large amounts, can germinate in a persons lungs causing a deadly infection that damages lung tissue and the circulatory system.Chapter Assessment

Chapter AssessmentQuestion 9Describe the process in which bacteria make nitrogen in the air accessible for use by plants.

Several species of bacteria have enzymes that convert nitrogen gas into ammonia. Other bacteria then convert the ammonia into nitrite and nitrate that plants can use.AnswerChapter Assessment

Chapter AssessmentQuestion 10What are the two ways in which bacterial diseases harm people?AnswerThe growth of the bacteria can interfere with the normal function of body tissue, or the bacteria can release a toxin that directly attacks the host.

Photo CreditsPhoto Credits Scott Ransom Centers for Disease Control, Atlanta, GA. Carolina Biological Supply Company USDA Lappa/Marquart

Photo CreditsPhoto Credits Diamar NOAA Wards Natural Science Est. Platinum PhotoDisc Alton Biggs

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End of Chapter 18 Show