《生物学》课程参考书籍文献（英文版，Chapter 32 - Chapter 48）Part IX Viruses and Simple Organisms、Part X Plant Form and Function、Part XI Plant Growth and Reproduction、Part XII Animal Diversity

Part IX Viruses and simple Organisms Electron micrograph of hepatitis virus. for Hepatitis c virus Responsible Discovering the Vi biotechnology company. What they did was shotgun clone the dna of infected cells. and then screen for hcv The genetic material of HCv, like that of many other You may not be aware that our country is in the midst of vIruses, is RNA. So the first step was to convert HCV RNA an epidemic of this potentially fatal liver disease. Almost to DNA, so that it could be cloned. There was no need to 4 million Americans are infected with the hepatitis C attempt to ach attempt to achieve entire faithful copies, a touchy and diffi- virus, most of them without knowing it. Some 9000 peo cult task, because they did not wish to replicate HCV, only ple will die this year in the United States from liver can identify it. So the researchers took the far easier route of cer and chronic liver failure brought on by the virus, and copying the virus RNa as a series of segments, each carry the number is expected to triple in the next decade. In g some part of the virus genome the first years of the new century, the number of annual Next, they inserted these DNA copies of HCV genes U.S. deaths caused by hepatitis C is predicted to overtake into a bacteriophage, and allowed the bacteriophage to in deaths caused by aIds fect Escherichia coli bacteria. In such a"shotgun"experi ment. millions of bacterial cells are infected with bacterio- epatitis is inflammation of the liver. Researchers in the phages. The researchers grew individual infected cells to 1940s identified two distinct forms. One. called infectious hepatitis or hepatitis A, is transmitted by contact with feces form discrete colonies on plates of solid culture media. The from infected individuals. A second form of hepatitis, called colonies together constituted a"cl serum hepatitis or hepatitis B, is passed only through the blood. Hepatitis B virus was isolated in the mid-1960s, he- essfully received HCV patitis A virus a decade later. This led in the 1970s to the o understand how they did this, focus on the quarry, a development of tests for the two viruses. Disturbingly, a cell infected with an HCV gene. Once inside a bacterial substantial proportion of hepatitis cases did not appear to cell, an HCv gene fragment becomes just so much more Clearly another virus was at work. At first, investigators lular machinery of the bacteria reads it just like bacterial thought it wouldn 't be long before it was isolated. How- genes, manufacturing the virus protein that the inserted ever. it was not until 1990 that researchers succeeded i HCV gene encodes. The secret is to look for cells with isolating the virus responsible for these"non-A, non-B HCV proteins cases, a virus that we now call hepatitis C virus(HCv). How to identify an HCV protein from among a back HCV was difficult to isolate because it cannot be grown ground of thousands of bacterial proteins? Houghton and reliably in a laboratory culture of cells. Making the prob- his colleagues tested each colony for its ability to cause a lem even more difficult, HCV is a strictly primate virus. It visible immune reaction with serum isolated from HCV infects only humans and our close relatives-chimpanzees infected chimpanzees and tamarins. Because it is very expensive to maintain The test is a very simple and powerful one, because its these animals in research laboratories, only small numbers success does not depend on knowing the identity of the of animals can be employed in any one study. Thus, the genes you seek. The serum of HCV-infected animals con- virus could not be isolated by the traditional means of pu- tains antibodies directed against a broad range of HCV rification from extracts of infected cells. What finally suc proteins encountered while combating the animals HCV ceeded, after 15 years of failed attempts at isolation, was infection. The serum can thus be used as a probe for the molecular technology. HCV was the first virus isolated en- presence of HCv proteins in other cells tirely by cloning the infectious nucleic acid Out of a million bacterial clones tested, just one was The successful experiment was carried out by Michael found that reacted with the chimp HCV serum, but not Houghton and fellow researchers at Chiron, a California with serum from the same chimp before infection. 647

647 Discovering the Virus Responsible for Hepatitis C You may not be aware that our country is in the midst of an epidemic of this potentially fatal liver disease. Almost 4 million Americans are infected with the hepatitis C virus, most of them without knowing it. Some 9000 peo￾ple will die this year in the United States from liver can￾cer and chronic liver failure brought on by the virus, and the number is expected to triple in the next decade. In the first years of the new century, the number of annual U.S. deaths caused by hepatitis C is predicted to overtake deaths caused by AIDS. Hepatitis is inflammation of the liver. Researchers in the 1940s identified two distinct forms. One, called infectious hepatitis or hepatitis A, is transmitted by contact with feces from infected individuals. A second form of hepatitis, called serum hepatitis or hepatitis B, is passed only through the blood. Hepatitis B virus was isolated in the mid-1960s, he￾patitis A virus a decade later. This led in the 1970s to the development of tests for the two viruses. Disturbingly, a substantial proportion of hepatitis cases did not appear to be caused by either of these two viruses. Clearly another virus was at work. At first, investigators thought it wouldn't be long before it was isolated. How￾ever, it was not until 1990 that researchers succeeded in isolating the virus responsible for these "non-A, non-B" cases, a virus that we now call hepatitis C virus (HCV). HCV was difficult to isolate because it cannot be grown reliably in a laboratory culture of cells. Making the prob￾lem even more difficult, HCV is a strictly primate virus. It infects only humans and our close relatives—chimpanzees and tamarins. Because it is very expensive to maintain these animals in research laboratories, only small numbers of animals can be employed in any one study. Thus, the virus could not be isolated by the traditional means of pu￾rification from extracts of infected cells. What finally suc￾ceeded, after 15 years of failed attempts at isolation, was molecular technology. HCV was the first virus isolated en￾tirely by cloning the infectious nucleic acid. The successful experiment was carried out by Michael Houghton and fellow researchers at Chiron, a California biotechnology company. What they did was shotgun clone the DNA of infected cells, and then screen for HCV. The genetic material of HCV, like that of many other viruses, is RNA. So the first step was to convert HCV RNA to DNA, so that it could be cloned. There was no need to attempt to achieve entire faithful copies, a touchy and diffi￾cult task, because they did not wish to replicate HCV, only identify it. So the researchers took the far easier route of copying the virus RNA as a series of segments, each carry￾ing some part of the virus genome. Next, they inserted these DNA copies of HCV genes into a bacteriophage, and allowed the bacteriophage to in￾fect Escherichia coli bacteria. In such a "shotgun" experi￾ment, millions of bacterial cells are infected with bacterio￾phages. The researchers grew individual infected cells to form discrete colonies on plates of solid culture media. The colonies together constituted a "clone library." The prob￾lem then is to screen the library for colonies that had suc￾cessfully received HCV. To understand how they did this, focus on the quarry, a cell infected with an HCV gene. Once inside a bacterial cell, an HCV gene fragment becomes just so much more DNA, not particularly different from all the rest. The cel￾lular machinery of the bacteria reads it just like bacterial genes, manufacturing the virus protein that the inserted HCV gene encodes. The secret is to look for cells with HCV proteins. How to identify an HCV protein from among a back￾ground of thousands of bacterial proteins? Houghton and his colleagues tested each colony for its ability to cause a visible immune reaction with serum isolated from HCV￾infected chimpanzees. The test is a very simple and powerful one, because its success does not depend on knowing the identity of the genes you seek. The serum of HCV-infected animals con￾tains antibodies directed against a broad range of HCV proteins encountered while combating the animal's HCV infection. The serum can thus be used as a probe for the presence of HCV proteins in other cells. Out of a million bacterial clones tested, just one was found that reacted with the chimp HCV serum, but not with serum from the same chimp before infection. Part IX Viruses and Simple Organisms Electron micrograph of hepatitis C virus

How the hepatitis C virus was discovered. Michael Houghton and fellow researchers identified the virus responsible for hepatitis C by making DNA copies of RNA from the cells of infected chimpanzees. They then cloned this DNA, using bacteriophages to carry it into bacterial cells. Colonies of the bacteria were then tested with serum from infected chimps. Any colony that produced an immune reaction would have to contain the virus Using this clone as a toehold the researchers were able Why not move vigorously to produce a vaccine directed to go back and fish out the rest of the virus genome from against hepatitis C? This turns out to be particularly difficult infected cells. From the virus genome, it was a straightfor- for this virus, because antibodies directed against it appear to ward matter to develop a diagnostic antibody test for the be largely ineffective. Those few individuals who do succeed presence of the HCV virus in clearing the virus from their bodies gain no immunity to Using the diagnostic test, researchers found hepatitis C subsequent infection. They produce antibodies directed to be far more common than had been supposed. This is a against the virus, but the antibodies don, t protect them. It ap- problem of major proportions, because hepatitis C virus is pears that hepatitis C virus evades our antibody defenses by unlike hepatitis A or B in a very important respect: it causes high mutation rates, just as the AIDS virus does. By the time chronic disease. Most viruses cause a brief, intense infec- antibodies are being produced against one version of the tion and then are done. Hepatitis A, for example, typically virus, some of the viruses have already mutated to a different lasts a few weeks. Ninety percent of people with hepatitis C form that the antibody does not recognize. Like chasing a ave it for years, many of them for decades burglar who is constantly changing his disguise, the antibod- All during these long years of infection, damage is being ies never learn to recognize the newest version of the virus done to the liver. Cells of the immune system called cyto- To date, attempts to develop a drug to combat hepatitis toxic T cells recognize hepatitis C virus proteins on the C virus focus on the virus itself. This virus carries just one surface of liver cells. and kill the infected cells. Over the gene, a very big one. When it infects liver cells, this gene years, many dead liver cells accumulate, and in response is translated into a single immense"polyprotein. "Enzyme the cells around them begin to secrete collagen and other then cut the polyprotein into 10 functional pieces. Each proteins to cover the mess. This eventually produces pro- piece plays a key role in building new viruses in infected tein fibers interlacing the liver, fibers which disrupt the liver cells. Some of these proteins form parts of the virus flow of materials through the liver's many internal pas- body, others are enzymes needed to replicate the virus sages. Imagine dropping bricks and rubble on a highway- gene. As you might expect, each of these 10 proteins is it gets more and more difficult for traffic to move as the being investigated as a potential target for a drug to fight rubble accumulates the virus, although no success is reported as yet. If this fibrosis progresses far enough, it results in com- Other attempts to fight hepatitis C focus on the part of plete blockage, cirrhosis, a serious condition which may in ur immune system that attacks infected liver cells. Unlike duce fatal liver failure, and which often induces primary the ineffective antibody defense, our bodies' cytotoxic T cells liver cancer. About 20% of patients develop cirrhosis clearly are able to detect and attack cells carrying hepatitis C within 20 years of infection proteins. A vaccine that stimulates these cytotoxic T cells Luckily, hepatitis C is a very difficult virus to transmit. might eliminate all infected cells at the start of an infection Direct blood contact is the only known path of direct trans- stopping the disease in its tracks before it got started. A seri- mission. Sexual transmission does not seem likely, although ous effort is being made to develop such a vaccine the possibility is still being investigated. Married partners It doesnt look like an effective remedy is going to be of infected individuals rarely get the virus, and its incidence available anytime soon. In the meantime, as the death rates among promiscuous gay men is no higher than among the from hepatitis C exceed those for AIDs in the next few la years, we can hope research will further intensify 648 Part IX Viruses and Simple organism

648 Part IX Viruses and Simple Organisms Using this clone as a toehold, the researchers were able to go back and fish out the rest of the virus genome from infected cells. From the virus genome, it was a straightfor￾ward matter to develop a diagnostic antibody test for the presence of the HCV virus. Using the diagnostic test, researchers found hepatitis C to be far more common than had been supposed. This is a problem of major proportions, because hepatitis C virus is unlike hepatitis A or B in a very important respect: it causes chronic disease. Most viruses cause a brief, intense infec￾tion and then are done. Hepatitis A, for example, typically lasts a few weeks. Ninety percent of people with hepatitis C have it for years, many of them for decades. All during these long years of infection, damage is being done to the liver. Cells of the immune system called cyto￾toxic T cells recognize hepatitis C virus proteins on the surface of liver cells, and kill the infected cells. Over the years, many dead liver cells accumulate, and in response the cells around them begin to secrete collagen and other proteins to cover the mess. This eventually produces pro￾tein fibers interlacing the liver, fibers which disrupt the flow of materials through the liver's many internal pas￾sages. Imagine dropping bricks and rubble on a highway— it gets more and more difficult for traffic to move as the rubble accumulates. If this fibrosis progresses far enough, it results in com￾plete blockage, cirrhosis, a serious condition which may in￾duce fatal liver failure, and which often induces primary liver cancer. About 20% of patients develop cirrhosis within 20 years of infection. Luckily, hepatitis C is a very difficult virus to transmit. Direct blood contact is the only known path of direct trans￾mission. Sexual transmission does not seem likely, although the possibility is still being investigated. Married partners of infected individuals rarely get the virus, and its incidence among promiscuous gay men is no higher than among the population at large. Why not move vigorously to produce a vaccine directed against hepatitis C? This turns out to be particularly difficult for this virus, because antibodies directed against it appear to be largely ineffective. Those few individuals who do succeed in clearing the virus from their bodies gain no immunity to subsequent infection. They produce antibodies directed against the virus, but the antibodies don't protect them. It ap￾pears that hepatitis C virus evades our antibody defenses by high mutation rates, just as the AIDS virus does. By the time antibodies are being produced against one version of the virus, some of the viruses have already mutated to a different form that the antibody does not recognize. Like chasing a burglar who is constantly changing his disguise, the antibod￾ies never learn to recognize the newest version of the virus. To date, attempts to develop a drug to combat hepatitis C virus focus on the virus itself. This virus carries just one gene, a very big one. When it infects liver cells, this gene is translated into a single immense "polyprotein." Enzymes then cut the polyprotein into 10 functional pieces. Each piece plays a key role in building new viruses in infected liver cells. Some of these proteins form parts of the virus body, others are enzymes needed to replicate the virus gene. As you might expect, each of these 10 proteins is being investigated as a potential target for a drug to fight the virus, although no success is reported as yet. Other attempts to fight hepatitis C focus on the part of our immune system that attacks infected liver cells. Unlike the ineffective antibody defense, our bodies' cytotoxic T cells clearly are able to detect and attack cells carrying hepatitis C proteins. A vaccine that stimulates these cytotoxic T cells might eliminate all infected cells at the start of an infection, stopping the disease in its tracks before it got started. A seri￾ous effort is being made to develop such a vaccine. It doesn't look like an effective remedy is going to be available anytime soon. In the meantime, as the death rates from hepatitis C exceed those for AIDS in the next few years, we can hope research will further intensify. How the hepatitis C virus was discovered. Michael Houghton and fellow researchers identified the virus responsible for hepatitis C by making DNA copies of RNA from the cells of infected chimpanzees. They then cloned this DNA, using bacteriophages to carry it into bacterial cells. Colonies of the bacteria were then tested with serum from infected chimps. Any colony that produced an immune reaction would have to contain the virus

32 How We classify Orgo Concept Outline 32.1 Biologists name organisms in a systematic way The Classification of Organisms. Biologists name organisms using a binomial system Species Names. Every kind of organism is assigned a The Taxonomic Hierarchy. The higher groups into which an organism is placed reveal a great deal about the organism. What Is a Species? Species are groups of similar organisms that tend not to interbreed with individuals of other groups. 32.2 Scientists construct phylogenies to understand the evolutionary relationships among organisms Evolutionary Classifications. Traditional and cladistic terpretations of evolution differ in the emphasis they place on particular traits. 32.3 All living organisms are grouped into one of a few FIGURE 32.1 major categories Biological diversity. All living things are assigned to particular The Kingdoms of Life. Living organisms are grouped classifications based on characteristics such as their anatomy into three great groups called domains, and within domains development, mode of nutrition, level of organization, and biochemical n. Coral reefs. like the one seen here are Domain Archaea(Archaebacteria). The oldest domain home to a variety of living things. consists of primitive bacteria that often live in extreme environments Domain Bacteria(Eubacteria). Too small to see with ll organisms share many biological characteristics. the unaided eye, eubacteria are more numerous than any A .They are composed of one or more cells, carry out other organism. metabolism and transfer energy with ATP, and encode Domain Eukarya(Eukaryotes). There are four hereditary information in DNA. All species have evolved kingdoms of eukaryotes, three of them entirely or predominantly multicellular. Two of the most important from simpler forms and continue to evolve. Individuals live haracteristics to have evolved among the eukaryotes are in populations. These populations make up communities multicellularity and sexuality and ecosystems, which provide the overall structure of life Viruses: A Special Case. Viruses are not organisms, and on earth. So far. we have stressed these common themes hus do not belong to any kingdom considering the general principles that apply to all organ isms. Now we will consider the diversity of the biologic world and focus on the differences among groups of organ isms(figure 32. 1). For the rest of the text, we will examine the different kinds of life on earth. from bacteria and amoe- bas to blue whales and

649 32 How We Classify Organisms Concept Outline 32.1 Biologists name organisms in a systematic way. The Classification of Organisms. Biologists name organisms using a binomial system. Species Names. Every kind of organism is assigned a unique name. The Taxonomic Hierarchy. The higher groups into which an organism is placed reveal a great deal about the organism. What Is a Species? Species are groups of similar organisms that tend not to interbreed with individuals of other groups. 32.2 Scientists construct phylogenies to understand the evolutionary relationships among organisms. Evolutionary Classifications. Traditional and cladistic interpretations of evolution differ in the emphasis they place on particular traits. 32.3 All living organisms are grouped into one of a few major categories. The Kingdoms of Life. Living organisms are grouped into three great groups called domains, and within domains into kingdoms. Domain Archaea (Archaebacteria). The oldest domain consists of primitive bacteria that often live in extreme environments. Domain Bacteria (Eubacteria). Too small to see with the unaided eye, eubacteria are more numerous than any other organism. Domain Eukarya (Eukaryotes). There are four kingdoms of eukaryotes, three of them entirely or predominantly multicellular. Two of the most important characteristics to have evolved among the eukaryotes are multicellularity and sexuality. Viruses: A Special Case. Viruses are not organisms, and thus do not belong to any kingdom. All organisms share many biological characteristics. They are composed of one or more cells, carry out metabolism and transfer energy with ATP, and encode hereditary information in DNA. All species have evolved from simpler forms and continue to evolve. Individuals live in populations. These populations make up communities and ecosystems, which provide the overall structure of life on earth. So far, we have stressed these common themes, considering the general principles that apply to all organ￾isms. Now we will consider the diversity of the biological world and focus on the differences among groups of organ￾isms (figure 32.1). For the rest of the text, we will examine the different kinds of life on earth, from bacteria and amoe￾bas to blue whales and sequoia trees. FIGURE 32.1 Biological diversity. All living things are assigned to particular classifications based on characteristics such as their anatomy, development, mode of nutrition, level of organization, and biochemical composition. Coral reefs, like the one seen here, are home to a variety of living things

2.1 Biologists name organisms in a systematic way The Classification of organisms Organisms were first classified more than 2000 years ago by the greek philosopher Aristotle, who categorized living things as either plants or animals. He classified ani mals as either land. water, or air dwellers and he divided plants into three kinds based on stem differences. This simple classifica- tion system was expanded by the greeks and Romans, who grouped anima ants into basic units such as cats, horses. and aks. Eventually, these units began to be Quercus phellos Quercus rubra called genera(singular, genus), the Latin Willow oak word for“ groups.” Starting in the Middle Ages, these names began to be systemati- FIGURE 32.2 cally written down, using Latin, the lan- Two species of oaks. (a) willow oak, Quercus pbellos (6)Red oak, Quercus rubra guage used by scholars at that time. Thus, Although they are both oaks (Quercus), these two species differ sharply in leaf shap cats were assigned to the genus Felis, horses and size and in many other features, including geographical range. to equus, and oaks to Quercus--names that the Romans had applied to these groups For genera that were not known to the Romans, new books, employed the polynomial system. But as a kind of names were invented shorthand. Linnaeus also included in these books a two- The classification system of the Middle Ages, called the part name for each species. For example, the honeybee be- polynomial systemm, was used virtually unchanged for hun- came Apis mellifera. These two-part names, or binomials dreds of years (bi,"two")have become our standard way of designating The Polynomial System a Closer look at linnaeus Until the mid-1700s, biologists usually descriptive terms to the name of the they called a species. These phrases, of organis a series o when they To illustrate Linnaeus's work further, let's consider how he wanted to refer to a particular kind of organism, which treated two species of oaks from North America, which ng with the 1753 had been described by scientists. He grouped all oaks in name of the genus, came to be known as polynomials the genus Quercus, as had been the practice since Roman (poly, "many; nomial,"name"), strings of Latin words and times. Linnaeus named the willow oak of the southeastern phrases consisting of up to 12 or more words. One name United States(figure 32.2a) Quercus foliis lanceolatus inte- for the European honeybee, for example, was Apis pube genTilis glai bris("oak with spear-shaped, smooth leaves with cens, thorace szbgriseo, abdomine fusco, pedibus posticus glabris absolutely no teeth along the margins"). For the common red utrinque margine ciliaris. As you can imagine, these poly- oak of eastern temperate North America(figure 32. 2b), Lin- nomial names were cumbersome. Even more worrisome, naeus devised a new name, Quercus foliis obtuse-sinuatis the names were altered at will by later authors, so that a setaceo-mucronatis ("oak with leaves with deep blunt lobes given organism really did not have a single name that was bearing hairlike bristles"). For each of these species, he also presented a shorthand designation, the binomial names Qn cus pbellos and Quercus rubra. These have remained the official The Binomial System names for these species since 1753, even though Linnaeus did not intend this when he first used them in his book. He con A much simpler system of naming animals, plants, and sidered the polynomials the true names of the species other organisms stems from the work of the Swedish biolo- t Carolus Linnaeus(1707-1778). Linnaeus devoted his life to a challenge that had defeated many biologists before Two-part("binomial")Latin names, first utilized by him--cataloging all the different kinds of organisms. In the Linnaeus, are now universally employed by biologists to 1750s he produced several major works that, like his earlier name particular organisms 650 Part IX Viruses and Simple organism

books, employed the polynomial system. But as a kind of shorthand, Linnaeus also included in these books a two￾part name for each species. For example, the honeybee be￾came Apis mellifera. These two-part names, or binomials (bi, “two”) have become our standard way of designating species. A Closer Look at Linnaeus To illustrate Linnaeus’s work further, let’s consider how he treated two species of oaks from North America, which by 1753 had been described by scientists. He grouped all oaks in the genus Quercus, as had been the practice since Roman times. Linnaeus named the willow oak of the southeastern United States (figure 32.2a) Quercus foliis lanceolatis inte￾gerrimis glabris (“oak with spear-shaped, smooth leaves with absolutely no teeth along the margins”). For the common red oak of eastern temperate North America (figure 32.2b), Lin￾naeus devised a new name, Quercus foliis obtuse-sinuatis setaceo-mucronatis (“oak with leaves with deep blunt lobes bearing hairlike bristles”). For each of these species, he also presented a shorthand designation, the binomial names Quer￾cus phellos and Quercus rubra. These have remained the official names for these species since 1753, even though Linnaeus did not intend this when he first used them in his book. He con￾sidered the polynomials the true names of the species. Two-part (“binomial”) Latin names, first utilized by Linnaeus, are now universally employed by biologists to name particular organisms. 650 Part IX Viruses and Simple Organisms The Classification of Organisms Organisms were first classified more than 2000 years ago by the Greek philosopher Aristotle, who categorized living things as either plants or animals. He classified ani￾mals as either land, water, or air dwellers, and he divided plants into three kinds based on stem differences. This simple classifica￾tion system was expanded by the Greeks and Romans, who grouped animals and plants into basic units such as cats, horses, and oaks. Eventually, these units began to be called genera (singular, genus), the Latin word for “groups.” Starting in the Middle Ages, these names began to be systemati￾cally written down, using Latin, the lan￾guage used by scholars at that time. Thus, cats were assigned to the genus Felis, horses to Equus, and oaks to Quercus—names that the Romans had applied to these groups. For genera that were not known to the Romans, new names were invented. The classification system of the Middle Ages, called the polynomial system, was used virtually unchanged for hun￾dreds of years. The Polynomial System Until the mid-1700s, biologists usually added a series of descriptive terms to the name of the genus when they wanted to refer to a particular kind of organism, which they called a species. These phrases, starting with the name of the genus, came to be known as polynomials (poly, “many”; nomial, “name”), strings of Latin words and phrases consisting of up to 12 or more words. One name for the European honeybee, for example, was Apis pubes￾cens, thorace subgriseo, abdomine fusco, pedibus posticis glabris utrinque margine ciliatis. As you can imagine, these poly￾nomial names were cumbersome. Even more worrisome, the names were altered at will by later authors, so that a given organism really did not have a single name that was its alone. The Binomial System A much simpler system of naming animals, plants, and other organisms stems from the work of the Swedish biolo￾gist Carolus Linnaeus (1707–1778). Linnaeus devoted his life to a challenge that had defeated many biologists before him—cataloging all the different kinds of organisms. In the 1750s he produced several major works that, like his earlier 32.1 Biologists name organisms in a systematic way. Quercus phellos (Willow oak) Quercus rubra (Red oak) FIGURE 32.2 Two species of oaks. (a) Willow oak, Quercus phellos. (b) Red oak, Quercus rubra. Although they are both oaks (Quercus), these two species differ sharply in leaf shape and size and in many other features, including geographical range

Species Names ing living things, and a of or stem is called a taxon ur taxonomists throughout the world, no two organisms can have the same name So that no one country is fa ored, a language spoken by no Latin--is used for the ganism is here in the world, this system provides a standard and precise way of communicating, whether the language of a particular (a) biologist is Chinese, Arabic, Spanish or English. This is a great improve ment over the use of common names which often vary from one place to the next. As you can see in figure 32.3, corn in Europe refers to the plant Americans call wheat; a bear is a large placental omnivore in the United States but a koala(a vegetar- ian marsupial) in Australia; and a robin is a very different bird in Eu- rope and North America lso by agreement the first word of the binomial name is the genus to which the organism belongs. Thi word is always capitalized. The sec ond word refers to the particular (b) species and is not capitalized. The two words together are called the scien tific name and are written in italics or distinctive print: for example, Homo sapiens. Once a genus has been used in the body of a text, it is often abbrevi- ated in later uses. For example, the di nosaur Tyrannosaurus rex becomes T. rex,and the potentially dangerous bacterium escherichia coli is known as E. coli. The system of naming animals, plants, and other organisms estab- lished by Linnaeus has served the sci- ence of biology well for nearly 230 By convention, the first part of a binomial species name identifies the genus to which the species FIGURE 32.3 belongs, and the second part distinguishes that particular Common names make poor labels. The common names corn(a), bear(6), and robin(c) species from other species in the bring clear images to our minds(photos on left), but the images are very different to someone living in Europe or Australia(photos on rigbt). There, the same common names are used to label very different species. Chapter 32 How We Classify Organisms 651

Species Names Taxonomy is the science of classify￾ing living things, and a group of or￾ganisms at a particular level in a clas￾sification system is called a taxon (plural, taxa). By agreement among taxonomists throughout the world, no two organisms can have the same name. So that no one country is fa￾vored, a language spoken by no coun￾try—Latin—is used for the names. Because the scientific name of an or￾ganism is the same anywhere in the world, this system provides a standard and precise way of communicating, whether the language of a particular biologist is Chinese, Arabic, Spanish, or English. This is a great improve￾ment over the use of common names, which often vary from one place to the next. As you can see in figure 32.3, corn in Europe refers to the plant Americans call wheat; a bear is a large placental omnivore in the United States but a koala (a vegetar￾ian marsupial) in Australia; and a robin is a very different bird in Eu￾rope and North America. Also by agreement, the first word of the binomial name is the genus to which the organism belongs. This word is always capitalized. The sec￾ond word refers to the particular species and is not capitalized. The two words together are called the scien￾tific name and are written in italics or distinctive print: for example, Homo sapiens. Once a genus has been used in the body of a text, it is often abbrevi￾ated in later uses. For example, the di￾nosaur Tyrannosaurus rex becomes T. rex, and the potentially dangerous bacterium Escherichia coli is known as E. coli. The system of naming animals, plants, and other organisms estab￾lished by Linnaeus has served the sci￾ence of biology well for nearly 230 years. By convention, the first part of a binomial species name identifies the genus to which the species belongs, and the second part distinguishes that particular species from other species in the genus. Chapter 32 How We Classify Organisms 651 (a) (b) (c) FIGURE 32.3 Common names make poor labels. The common names corn (a), bear (b), and robin (c) bring clear images to our minds (photos on left), but the images are very different to someone living in Europe or Australia (photos on right). There, the same common names are used to label very different species