The Classification of Living Things

SECTION 11.3 The Classification of Living Things EXPECTATIONS Define the fundamental principles of taxonomy. Demonstrate the usefulness of the system of scientific nomenclature. Construct a key for the identification of different organisms. Figure 11.11 Features such as petals are used to classify flowering plants into different groups or taxa. When detectives ask an eyewitness to describe a getaway vehicle, the more specific the description the witness gives, the more likely it is that the detectives will be able to identify the car. The model, colour, and year of the car all narrow down the search. But there may still be hundreds or thousands of vehicles that fit this description. Of course, the license plate number is the best evidence of all. Together with the other details, it accurately describes one particular car. In the same way, biologists need specific details to identify organisms. For example, if you ask a zoologist to help you identify a species of bird, it is not very useful to describe the bird as small and brown. Many dozens of species of small brown birds live in Canada. One purpose of a classification system, therefore, is to allow the accurate identification of a particular organism. The practice of classifying organisms is known as taxonomy (taxis means arrangement and nomos means law). The system of taxonomy used by scientists today was founded nearly 300 years ago by a Swedish botanist named Carolus Linnaeus (1707 1778). Linnaeus used simple physical characteristics to identify different species and organize them into groups. For example, he based his classification of flowering plants, like the one shown in Figure 11.11, on the number and arrangement of features such as petals and stamens. Using this system, people could accurately identify an organism by comparing its appearance against a checklist of characteristics. During the 1700s, explorers from Europe were discovering more and more of the world s rich diversity of plants and animals including many species Europeans had never seen before. Thanks to the work of Linnaeus, they were able to classify these unknown organisms into groups of similar species. Linnaeus s system was so easy to use that it quickly became popular. Naming Organisms Biologists still use Linnaeus s method of naming each species using two words, such as Felis domesticus (the house cat). Many of these names are based on Latin or Greek words because when Linnaeus developed his system of classification in the 1700s, these classical languages were the common languages of science. When scientists find and describe new species, they are required to give the species a Latin scientific name. These names often reflect characteristics of the organisms, or in other cases, the names are given to honour a fellow scientist or historical figure. Latin continues to be used for these new names. 390 MHR Diversity of Living Things

Figure 11.12 A bee, shark, horse, dog, and oyster are all members of the animal kingdom. Hierarchy of Groups As members of the animal kingdom, the bee, shark, horse, dog, and oyster shown in Figure 11.12 have certain things in common. On the other hand, these animals are obviously not very much alike. There are different degrees of similarity among animals. For example, a horse is more like a dog than like a shark (horses and dogs are mammals; sharks are fish). However a horse is more like a shark than like an oyster (horses and sharks are vertebrates; oysters are invertebrates). To distinguish such different degrees of similarity, each kingdom is subdivided several times into a series of progressively smaller groups. Each group is called a taxon (plural taxa). Kingdoms are the largest and most general taxa they include many thousands of species. are the smallest taxa they include only a single type of organism. Between kingdoms and species, organisms are classified into a minimum of five other taxa, which form a hierarchy of groups. Table 11.2 lists the names of these taxa and gives an example of each. In some systems, additional taxa are used to help subdivide large groups. For example, subphylum is an added taxon between phylum and class. PAUSE RECORD Over 75% of named living species belong to the phylum Arthropoda, which includes such diverse organisms as lobsters, crabs, shrimp, barnacles, sow bugs, scorpions, spiders, mites, millipedes, and insects. The insects are by far the most abundant arthropods. What physical characteristic(s) do you think all arthropods have in common? List your ideas and explain them briefly. Table 11.2 An example of hierarchical classification Taxon Example Organisms included in this taxon Kingdom Phylum Class Order Family Genus Felidae Lynx Lynx canadensis Lynx rufus bee, shark, horse, oyster, frog, dog, cougar, lynx, bobcat shark, horse, frog, dog, cougar, lynx, bobcat horse, dog, cougar, lynx, bobcat dog, cougar, lynx, bobcat cougar, lynx, bobcat lynx, bobcat lynx bobcat You can see from Table 11.2 that a species is classified in a particular taxon at every level of the hierarchy. For example, a bobcat is a member of the Kingdom, the phylum, the class, and so on. As you move down the table, each taxon contains fewer species. As well, the smaller the taxon, the more similar the organisms within it. The taxon species includes members that resemble each other so closely that they can interbreed and produce fertile offspring. REWIND To learn about the genetic basis for differences among species, turn to Chapter 6, Section 6.1. Patterns of Life MHR 391

Investigation 11 A SKILL FOCUS Creating a Dichotomous Key If you find an insect you have never seen before, how could you discover its identity? Many field guides help you match up the characteristics of your specimen with those of similar organisms using a dichotomous key. This identification key uses a series of paired comparisons to sort organisms into smaller and smaller groups. In this investigation, you will learn how to make your own keys to identification. Performing and recording Analyzing and interpreting Communicating results Pre-lab Questions What characteristics do all insects have in common? Name two characteristics that scientists use to tell different insects apart. Problem How do you make a dichotomous key? Prediction Predict which characteristics of insects will be most useful in creating an identification key. Materials illustration of 18 s paper sample dichotomous keys pencil Procedure 1. Copy the diagram of a dichotomous tree shown here onto a separate piece of paper. group 7 group 3 All s group 1 group 2 group 4 group 5 group 6 group 8 group 9 group 10 group 11 group 12 group 13 group 14 2. Study the illustration of 18 s shown on the next page. 3. Select one characteristic and sort the s into two groups based on whether they have the characteristic or not. 4. List each s number under either Group 1 or Group 2 on your diagram. 5. Record the characteristic that identifies each group. 6. Select another characteristic of each subgroup, and repeat steps 4 and 5 for the next level down on your diagram. 7. Continue to subdivide the groups until you have 18 groups with one in each. 392 MHR Diversity of Living Things

8. Using the characteristics shown on your diagram, construct a dichotomous key that someone could use to identify any from the original large group. To do this, create a series of numbered steps with the first step showing the first characteristic you used. At each step, offer two choices for classifying the based on a single characteristic. For example, you may have used the characteristic antennae longer than front legs as your first dividing characteristic. Your first numbered step in your key would be (1a) antennae longer than front legs or (1b) antennae not longer than front legs. Use the sample keys provided by your teacher to help you. 9. Exchange your key with a partner. Use your partner s key to classify a, and record all the characteristics of the species you chose. Post-lab Questions 1. Did your partner produce a dichotomous key identical to yours? Explain why or why not. 2. Which characteristics were not useful for creating your key? Explain why not. Conclude and Apply 3. Why does a key offer two choices at each step and not more than two? 4. In your own words, define a dichotomous key. Exploring Further 5. Your teacher will provide you with several different mystery s. Use your dichotomous key and see if you can identify what species the s are. You may be unable to completely identify your using your key. If this is the case, how far could you go with your key? Visit the library or the Internet and get a field guide to s. Use this to identify the mystery s. What characteristics would you have needed in your key in order to fully identify them? 1 2 3 4 5 6 Variegated mudloving Mycetaeid Apricot borer Water tiger Predaceous diving Crawling water 7 8 9 10 11 12 Flathead apple borer Red-necked cane borer Cucumber snout Whirligig Ironclad Broad-horned flour 13 14 15 16 17 18 Red flour Blind ant- False wireworm White-marked spider Monterey cyprus Drug store Patterns of Life MHR 393

The system of using a two-word name for each species is called binomial nomenclature. The first word is the name of the genus (plural genera) in which the organism is classified. The first letter of this name is capitalized. Because a genus may contain more than one species, there may be several species with the same first name. For example, the genus Canis includes Canis lupus (wolf), Canis latrans (coyote), and Canis familiaris (domestic dog). The fact that these three animals have the same first name tells you that they are all in the same genus of dog-like animals and are very similar to one another. The second word in the name identifies the particular species. Thus, each species name has a unique two-word combination. THINKING LAB Classifying Dinner Background For dinner one evening, you are served a seafood stew containing lobster, squid, mussels, and two types of oysters. In the same way that the marine organisms are mixed up together in your bowl, the various names of the taxa that identify these five species are mixed up in the chart to the right. In this lab, you will redraw the chart and place each organism in its proper taxon at each level of the hierarchy. Common name Phylum Class Order Family Genus Market squid, American lobster, blue mussel, Virginia oyster, European oyster Arthropoda, Mollusca, Mollusca, Mollusca, Mollusca Malacostraca, Bivalvia, Bivalvia, Bivalvia, Cephalopoda Decapoda, Decapoda, Mytiloida, Pterioida, Pterioida Ostreidae, Ostreidae, Nephropidae, Mytilidae, Loliginidae Homarus, Mytilus, Ostrea, Loligo, Crassostrea americanus, virginica, edulis, edulis, opalescens You Try It 1. Draw a chart with six columns and seven rows. At the top of the first column, write Taxon. At the top of each of the other columns, write the common name of one organism from the chart. Label the rows: Phylum, Class, Order, Family, Genus, and, matching the order on the chart. Use reference books or the Internet to gather enough information to classify each organism correctly at each taxon level. 2. According to your classification scheme, which is the only taxon level in which all five organisms have a different name? Which order name is found in both the Arthropoda and Mollusca phyla (plural of phylum)? What does this name mean? Which two genera (plural of genus) have species with names containing the same word? What does this word mean? 3. Which two organisms are most closely related to each other? Give a reason for your answer. Which organism is least closely related to the other four? Give a reason for your answer. 394 MHR Diversity of Living Things

Common Names You may wonder what is wrong with referring to organisms by their everyday names, such as cat. Common names are not precise. The animal you think of when you hear the word cat may not be the same animal being described. There are different species of cats, such as wild cats and ringtailed cats. Animals such as lions and tigers are also called cats. In addition, people in different regions may use different common names to refer to the same species. For example, puma, cougar, and mountain lion are three different common names for the same animal. Over 300 different species of trees around the world are called mahogany. Each has its own scientific name. Common names can give you misleading ideas about the basic characteristics of an organism and the group in which it should be classified. For example, should shellfish, starfish, jellyfish, crayfish, and catfish all be in the single group, fish? All these organisms are animals that live in water, but there are more significant differences between a shellfish and a starfish than between a catfish and you. In fact, biologists place each of these five members of the animal kingdom in a separate phylum (Figure 11.13). A shellfish: phylum Mollusca B starfish: phylum Echinodermata C jellyfish: phylum Cnidaria D crayfish: phylum Arthropoda E catfish: phylum Figure 11.13 The common names of all these animals include the word fish, but each animal is classified in a different phylum. You are classified in the same phylum as a catfish. (A) Shellfish (Pacific pink scallop): Chlamys hericia (B) Starfish (vermilion star): Mediaster aequalis (C) Jellyfish (upsidedown jellyfish): Cassiopea xamachana (D) Crayfish (blue crayfish): Cambarus bartoni (E) Catfish (channel catfish): Ictalurus punctatus Patterns of Life MHR 395

The same common name may be used for different species. For example, the bird called a robin in Canada is a different species from the bird called a robin in Great Britain (Figure 11.14). A B Figure 11.14 Bird A is called a robin in Canada. Bird B, a different species, is called a robin in Great Britain. SECTION REVIEW 1. K/U List two reasons why the system of binomial nomenclature is useful. 2. K/U Cats, goldfish, and humans are in the same phylum. What characteristics do they have in common? What characteristics place cats and humans in a different order from goldfish? 3. I Based on your own knowledge, place the following species into three different phyla: ant, crow, spider, turtle, salmon, snail, octopus. 4. I The Greek philosopher Aristotle classified animals based on where they lived. Classify objects in your classroom in the same way, based on where they are found. Organism Kingdom House cat Dog 5. Phylum I Referring to the table shown here, which two animals are most closely related? Explain your answer. Class Order 6. Family I The information in this Felidae Canidae table shown here shows that a skunk is more closely related to a coyote than it is to a bat. Explain how you know this. Genus Felix domesticus Canis familiaris 7. I What kind of an animal is Myotis myotis? How do you know? Use the table shown here to help you. 8. C Using the information contained in the table shown here, create a display showing the relationships of the organisms. You may draw them, create a flow chart or a concept map, or you may even create a key. 9. MC There is a growing concern worldwide about the numbers of species that are going extinct. Conservation organizations work to protect endangered species, however, there may be disagreement about what exactly a species is. How can naming an organism influence our attitudes about that organism? For example, is a fish more likely to be protected if it is a known endangered species, or if it is newly discovered and different from all known species of fish? How can a name influence our feelings about a particular organism? Discuss this topic and write a short essay about your ideas. Coyote Canidae Canis latrans Skunk Mustelidae Mephitis mephitis UNIT ISSUE PREP Brown bat Chiroptera Vespertilionidae Myotis lucifugus Praying mantis Arthropoda Insecta Mantodea Mantidae Stagmomantis carolina You have just learned about how scientists name and classify organisms. You will be picking an endangered species to study for your Unit 4 Issue Analysis. Does the species that you are considering have a common name? What are the organisms names in binomial nomenclature? Make sure you are considering organisms based on their proper Latin names, not the common names that might be confusing. 396 MHR Diversity of Living Things