Lesson 24 lassification You will learn how organisms are placed into various groups based on similarities and differences shared among groups. You will also learn how to use guidelines to identify an organism. lassification key consists of a sequence of steps that are followed to identify an organism based on its observable features, such as structures and habitat. lip GUIE INSTRUTION IRETIONS Read the following information and answer the questions. The beginnings of taxonomy can be traced back to over 2000 years ago. At that time, Aristotle classified a living thing as either an animal or a plant. Aristotle's system was used for over 1600 years. Then in the 1700s, Swedish scientist arolus Linnaeus developed a new and more complex system. Not surprisingly, Linnaeus classified all living things mainly on the basis of their structure and shape. However, he greatly expanded the system used for classifying organisms. Linnaeus developed a seven-level classification system. Although it has been slightly modified, this system is still used today, Like Aristotle, Linnaeus classified living things as either animal or plant. Linnaeus used the term kingdom for his largest category. He then classified organisms into smaller and smaller categories. The smaller a category became, the more alike the organisms were. Linnaeus's seven-level classification system is shown in the illustration. Order Species Guided Questions What contribution did Linnaeus make to taxonomy? What are the seven levels of classification Linnaeus introduced? Now look at the table below to see how three different organisms a horseshoe crab, a blue crab, and a black widow spider fit into this classification system. lassification Level Horseshoe rab lue rab lack Widow Spider Kingdom Animalia Animalia Animalia Phylum Arthropoda Arthropoda Arthropoda lass Merostomata Malacostraca Arachinda Order Xiphosurida ecapoda Aranaea Family Limulidae Portunidae Theridiidae Genus Limulus allinectes Latrodectus Species Polyphemus Sapidus Mactans Peoples Education opying is illegal. hapter 3 iological Evolution and lassification 171
Lesson 24 lassification Notice that all three organisms belong to the same kingdom and phylum. All members of the phylum Arthropoda have a body that is divided into distinct parts called segments. Attached to these segments are appendages, such as legs or antennae. Arthropods also have a hard protective body covering, known as an exoskeleton or more commonly known as a shell. Guided Questions Identify three characteristics shared by all arthropods. Notice also that, although all three organisms are in the same kingdom and phylum, each is then placed in a different class. Interestingly, horseshoe crabs are the only arthropods in the class Merostomata. Organisms in this class are arthropods whose mouth is surrounded by legs. The term merostomata comes from Greek and means "legs attached to the mouth." Members of the class Malacostraca have legs attached to body segments but not their mouths. Members of the class Arachinda do not have antennae. onsequently, as you proceed through the seven-level classification system, the criteria used to classify organisms become more specific. Eventually, when the species level is reached, only a single type of organism remains. In effect, the classification levels become more exclusive in going from kingdom to species. Scientists use the genus and species names to identify an organism. This is known as binomial nomenclature. For example, scientists refer to a horseshoe crab as Limulus polyphemus and to a blue crab as allinectus sapidus. This avoids any possible confusion about the identity of an organism because the same animal can have several common names. An example is an animal that is known as a cougar, puma, mountain lion, mountain cat, catamount, or panther, depending on where it lives. No matter where a scientist lives, there is no confusion because the animal is known scientifically as Puma concolor. What does the term binomial nomenclature mean? The classification of the horseshoe crab, blue crab, and black widow spider can be misleading. All three organisms may seem to be equal in terms of their similarities. After all, they are all classified in the same kingdom and phylum and only begin to diverge at the class level. However, horseshoe crabs are more closely related to spiders than they are to blue crabs. lue crabs have antennae. In contrast, both horseshoe crabs and spiders do not have antennae. lue crabs also have gills. oth horseshoe crabs and spiders use a structure known as a book lung to obtain oxygen. Going through the seven levels of classification to identify an organism can be quite time consuming. This task can be even more difficult because scientists have added more levels to the classification systems. These additional levels include subphylum and subspecies. For example, the domesticated dog has the scientific name anis lupus familiaris to distinguish it from a closely related animal. This animal is the wolf, which has the scientific name anis lupus. In other words, domesticated dogs are classified as a subspecies of the genus that also includes the wolf. What two classification levels have been added since Linnaeus's time? 172 iology End-of-ourse opying is illegal. Measuring Up to the iology End-of-ourse el
lassification To help identify an organism more quickly, a classification key can be used. A classification key consists of a sequence of steps that is followed to identify an organism. Each step usually describes a structural feature, such as the presence or absence of wings. Many classification keys consist of steps that offer two choices. Such classification keys are called dichotomous keys. An example of a dichotomous key is shown below. This key can be used to help identify the type of tree found in Texas from which a leaf came. In some steps, this dichotomous key may identify three types of trees as a possible answer. A much more detailed dichotomous key would help identify the specific type of tree. Guided Questions What is a classification key? ichotomous key 1. a. Leaves are broad Go to Step 2 b. Leaves are needle-like Go to Step 3 2. a. Leaves and buds form opposite each other Maple, ash or dogwood tree b. Leaves and buds form an alternative arrangement Go to Step 5 3. a. Needles in clusters or bundles Pine tree b. Needles are individual Go to Step 4 4. a. Needles roll between fingers Spruce tree b. Needles do not roll between fingers Hemlock tree 5. a. Leaves are compound Walnut, sumac, or locust tree b. Leaves are simple Go to Step 6 6. a. Leaves have no lobes Go to Step 7 b. Leaves have lobes Go to Step 8 7. a. Leaves have smooth edges b. Leaves have rough edges 8. a. Leaves have round lobes b. Leaves have pointed lobes Willow oak, redbud, or magnolia tree irch, beech, or cherry tree White oak, mulberry, or sassafras tree Red oak, holly, or sycamore tree e Peoples Education opying is illegal. hapter 3 iological Evolution and lassification 173
Lesson 24 lassification 11lip SHORT-ANSWER QUESTIONS IRETIONS Answer the following questions. 1. How can two members of the same kingdom belong to different species, while two members of the same species must belong to the same kingdom? 2. What feature of organisms did Linnaeus use to develop his seven levels of classification? 3. Which classification level contains organisms that share more features order or family? Explain the reason for your choice. 4. Which two classification categories are used for the scientific name of an organism? 5. How does a classification key help identify an organism? 174 iology End-of-ourse opying is illegal. Measuring Up to the iology End-of-ourse Exam
lassification Lesson 24 Jr APPLY THE TEKS IRETIONS Read the paragraph, study the diagram, and answer the questions. Like a classification system, the military is organized into a hierarchical structure. For example, a soldier is the basic unit of the military. In turn, twelve soldiers make up a squad. Two or more squads make up a platoon. Two or more platoons make up a company. Two or more companies make up a battalion. Two or more battalions make up a regiment. Finally, two or more regiments make up a brigade. omplete the following table to show how both the classification system and the military consist of a hierarchical structure. Notice that the table contains one entry. iological Organization Military Organization Family Peoples Education opying is illegal. hapter 3 iological Evolution and lassification 175
Lesson 24 lassification STAAR PRATIE IRETIONS Read each question and choose the best answer. Then circle the letter for the correct answer. 1 Which classification level represents the least exclusive group of organisms? A lass Species Family Genus 2 What is the advantage of using an organism's scientific name rather than its common name? A The scientific name is always given in the native language. The scientific name is based upon the organism's kingdom and phylum. The scientific name does not depend on any classification system. The scientific name clearly identifies the organism. 3 A classification key can be considered a tool. What is the reason? A ' A classification key makes it easier to classify an organism. A classification key is used to unlock the criteria used for classifying organisms. A classification key makes it easier to identify an organism. A classification key is the reason why organisms are placed in the same classification level. 4 The Texas longhorn cattle have the scientific name os bos. What can you conclude from this fact? A The term longhorn cattle can also be considered its scientific name. The seven-level classification system does not apply to these cattle. The genus and species names are the same. Organisms with this scientific name are found only in Texas. 176 iology End-of-ourse opying is illegal. Measuring Up to the iology End-of-ourse Exam
lassification Lesson 24 41lip PRATIE: UMULATIVE IRETIONS Read each question and choose the best answer. Then circle the letter for the correct answer. The classification of life is not an easy task because of the wide diversity of organisms that are found on Earth. Which process was responsible for this wide diversity of life? A reeding strategies Natural selection Mitosis Gene flow 3 The classification system reveals the wide variety of life that exists. Each species of organisms has a unique set of features. Which of the following is responsible for creating the features that are used to classify organisms? A ell specialization Replication Taxonomy lassification keys The highest level of classification Linnaeus developed was the kingdom. Which of the following would represent an even higher level of classification? A Habitat Territory omain iome 4 The Texas longhorn cattle, os bos, evolved from an ancestor with the scientific name os primigenius. What can you conclude from this information? A They are members of different families They share their genus name. They share their species name. They belong to the same subspecies. Peoples Education opying is illegal. hapter 3 iological Evolution and lassification 177