Classifying Living Things

Classifying Living Things

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Games      Cladograms

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How would you find your favorite fresh fruit or vegetable in the grocery store?

 

You might look in the produce section, such as the one shown in Figure 1. Different kinds of peppers are displayed in one area. Citrus fruits such as oranges, lemons, and grapefruits are stocked in another area. There are many different ways to organize produce in a grocery store. In a similar way, there have been many different ideas about how to organize, or classify, living things.

 

A Greek philosopher named Aristotle (384 B.C.−322 B.C.) was one of the first people to classify organisms. Aristotle placed all organisms into two large groups, plants and animals. He classified animals based on the presence of “red blood,” the animal’s environment, and the shape and size of the animal. He classified plants according to the structure and size of the plant and whether the plant was a tree, a shrub, or an herb.

PhotoLink/Getty Images

Figure 1 The produce in this store is classified into groups.

Visual Check What other ways can you think of to classify and organize produce?

Answers will vary but may include color, shape, size, type.

 

 

1 NOTE

Determining Kingdoms

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Use the questions below to check for understanding.

Guiding Questions

What contribution did Carolus Linnaeus make to science?

He set up a classification system that divided living things into two groups, or kingdoms.

How does the classification system developed by Robert H. Whittaker differ from the one developed by Linnaeus?

Whittaker’s system is more detailed and includes five kingdoms instead of Linnaeus’s two.

Determining Kingdoms

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In the 1700s, Carolus Linnaeus, a Swedish physician and botanist, classified organisms based on similar structures. Linnaeus placed all organisms into two main groups, called kingdoms. Over the next 200 years, people learned more about organisms and discovered new organisms. In 1969 American biologist Robert H. Whittaker proposed a five-kingdom system for classifying organisms. His system included kingdoms Monera, Protista, Plantae, Fungi, and Animalia.

 

1 NOTE

SCIENCE USE V. COMMON USE

Have students read the science use and common use definitions. The common use for kingdom has rankings. There’s a king or queen, knights, bishops, and others. Each group of individuals in the kingdom is ranked according to its power within the kingdom.

Ask: How is the science use of kingdom similar to the common use?

A kingdom is part of the ranking in the classification system.

SCIENCE USE V. COMMON USE

kingdom
Science Use a classification category that ranks above phylum and below domain

Common Use a territory ruled by a king or a queen

 

2 NOTES

Determining Domains

To help students understand why scientists wanted to create a detailed classification system, ask them to think about the following questions.

Guiding Questions

Key Concept Check What evidence is used to classify living things into groups?

cell type, habitat, how the organism obtains food and energy, common ancestry, molecules within an organism (such as DNA)

What is systematics?

Systematics is a classification system that is more detailed than the one developed by Whittaker.

Visual Literacy: Table 1

Refer students to Table 1 and its abridged version below. Read the terms across for the different domains and kingdoms. Note the example and have students read the characteristics of each kingdom.

Determining Domains

The classification system of living things is still changing. The current classification method is called systematics. Systematics uses all the evidence that is known about organisms to classify them. This evidence includes an organism’s cell type, its habitat, the way an organism obtains food and energy, structure and function of its features, and the common ancestry of organisms. Systematics also includes molecular analysis—the study of molecules such as DNA within organisms.

 

Using systematics, scientists identified two distinct groups in Kingdom Monera—Bacteria and Archaea (ar KEE uh). This led to the development of another level of classification called domains. All organisms are now classified into one of three domains—Bacteria, Archaea, or Eukarya (yew KER ee uh) —and then into one of six kingdoms, as shown in Table 1.

1. Key Concept Check What evidence is used to classify living things into groups?

cell type, habitat, how the organism obtains food and energy, common ancestry, molecules within an organism (such as DNA)

Table 1 Domains and Kingdoms

 

10 NOTES

Scientific Names

Write the term binomial nomenclature on the board or chart paper. Read the term slowly and repeat, having students read it with you. Remind students that Carolus Linnaeus lived in the 1700s, yet his naming system is still used.

Binomial Nomenclature

Use the following questions to discuss Table 2.

Guiding Questions

What do you notice about taxonomic groups as you go down the list?

Each group has fewer animals in it (becomes more selective).

Visual Check What domain does the brown bear belong to?

domain Eukarya

How do species and genus relate to kingdoms and domains?

Similar species are grouped into one genus, just as similar kingdoms are grouped into one domain.

Visual Literacy: Figure 2

Direct students’ attention to Figure 2. Read the caption aloud. Write the scientific names on the board or chart paper. Explain that some people may commonly refer to both trees in the photo as evergreens, although the trees are different.

Ask: What is the same about what you see in this photo? What is different?

Both are trees; one has short needles, and one has long needles.

Ask: How can you tell these trees are two different species?

The needles of the two trees are different in shape and size.

Uses of Scientific Names

Guiding Questions

What is true about scientific names?

They are the same worldwide.

Key Concept Check Why does every species have a scientific name?

Scientific names allow people all over the world to identify an organism because each scientific name is unique and applies to only one type of organism.

Why would a group of scientists prefer to use the scientific name instead of the common name for a particular type of plant?

The scientific name refers to a specific species, so by using it, all the scientists know they are talking about the same plant.

Differentiated Instruction

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Kingdoms Have students create a collage using their own drawings or pictures cut out from old magazines on the six kingdoms. Encourage students to be creative in designing their collages.

Differentiated Instruction

The Classification Puzzle Have students work in pairs to create a puzzle that shows how one taxonomic group fits into those above it in the classification system.

1. Students need to use the taxonomic group names in their puzzles.

2. Students should share their puzzles with the class, reading the terms and describing how the puzzle works.

Differentiated Instruction

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Binomial Nomenclature Have students work in pairs to create a table on Eukarya Plantae similar to Table 2. Encourage students to create illustrations for their tables.

Fun Fact

Family Ursidae The family Ursidae includes eight species of bears found on all continents except Australia and Antarctica, and ranging in size from bears as small as the tropical sun bear (Helarctos malayanus) at 25 kg to the polar bear (Ursus maritimas) that can weigh up to 800 kg.

Careers in Science

Working with Classification Systems There are many careers that involve working with classification systems. Enthusiastic science students may want to think about a career as a zoologist. Many zoologists specialize in one animal family. Becoming a zoologist takes several years of college, but students who want to start working with animals sooner may want to volunteer at a zoo, or take classes to become an assistant at a zoo or nature center.

Reading Strategy

Reading Scientific Names Some scientific names can be difficult to read and remember. Break the scientific names into syllables. Write the accented syllable in capital letters. Read the names aloud, exaggerating the accented syllables.

Scientific Names

Suppose you did not have a name. What would people call you? All organisms, just like people, have names. When Linnaeus grouped organisms into kingdoms, he also developed a system for naming organisms. This naming system, called binomial nomenclature (bi NOH mee ul · NOH mun klay chur), is the system we still use today.

 

Binomial Nomenclature

Linneaus’s naming system, binomial nomenclature, gives each organism a two-word scientific name, such as Ursus arctos for a brown bear. This two-word scientific name is the name of an organism’s species (SPEE sheez). A species is a group of organisms that have similar traits and are able to produce fertile offspring. In binomial nomenclature, the first word is the organism’s genus (JEE nus) name, such as Ursus. A genus is a group of similar species. The second word might describe the organism’s appearance or its behavior.

 

How do species and genus relate to kingdoms and domains? Similar species are grouped into one genus (plural, genera). Similar genera are grouped into families, then orders, classes, phyla, kingdoms, and finally domains, as shown for the grizzly bear in Table 2.

Table 2 The classification of the brown bear or grizzly bear shows that it belongs to the order Carnivora.

Visual Check What domain does the brown bear belong to?

domain Eukarya

 

Uses of Scientific Names

When you talk about organisms, you might use names such as bird, tree, or mushroom. However, these are common names for a number of different species. Sometimes there are several common names for one organism. The animal in Table 2 might be called a brown bear or a grizzly bear, but it has only one scientific name, Ursus arctos.

 

Other times, a common name might refer to several different types of organisms. For example, you might call both of the trees in Figure 2 pine trees. But these trees are two different species. How can you tell? Scientific names are important for many reasons. Each species has its own scientific name.

 

Scientific names are the same worldwide. This makes communication about organisms more effective because everyone uses the same name for the same species.

 

1. Key Concept Check Why does every species have a scientific name?

Scientific names allow people all over the world to identify an organism because each scientific name is unique and applies to only one type of organism.

Mark Steinmetz

Figure 2 These trees are two different species. Pinus alba has long needles, and Tsuga canadensis has short needles.

 

1 NOTE

WORD ORIGIN

Have students read the word origins for genus. Discuss how knowing word origins can help in understanding new vocabulary words.

Ask: What are some different kinds of dogs?

Answers will vary. Students should respond with collie, husky, retriever, and so on.

Discuss how all the dogs belong to the same genus (genus Canis), but that each has traits that are unique, such as body size, head shape, and ear shape.

WORD ORIGIN

genus
from Greek genos, means “race, kind”

 

7 NOTES

Classification Tools

Ask students to identify different tools, such as hammers and drills, and explain how each tool helps accomplish a task. Tell students that classification tools help them accomplish the task of identifying organisms.

Dichotomous Keys

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Refer students to Figure 3. Write the word dichotomous on the board, divide it into syllables, and read it aloud. Tell students that dichotomous means “divided into two parts.” Read the caption aloud. Have students compare and contrast two of the fish shown in Figure 3. Create a Venn diagram with comparisons of both fish noted in the center overlap, and contrasts noted in each outside circle.

Guiding Questions

What is a dichotomous key?

A series of questions used to identify an unknown organism.

How is a dichotomous key used to identify an organism?

The reader answers a series of questions related to similar organisms until a specific organism is identified.

How do the questions of a dichotomous key help the reader identify an organism?

The questions refer to specific characteristics of a group of similar animals.

Cladograms

After students read the first paragraph, use the scaffolded questions below to connect the information in the paragraph to Figure 4.

Guiding Questions

What is a cladogram?

A cladogram is a branched diagram that shows how organisms are related.

How is a cladogram read?

All organisms to the right of a characteristic noted on the cladogram have that characteristic. Those organisms to the left do not.

Which animals on a cladogram are closely related to each other?

Organisms to the right of a characteristic noted on the cladogram are more closely related.

Differentiated Instruction

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Same and Different Have students work in small groups to draw or find images of four different kinds of birds. Students should use the images to create a dichotomous key poster. Have each student group share their dichotomous key with the class.

Differentiated Instruction

Create a Cladogram Have students work in small groups to create a cladogram using different animals than the ones shown in Figure 4. Have students share and explain their cladograms with the class.

Differentiated Instruction

Classification Tools Provide students with a stiff piece of paper and several smaller pieces of paper to use for making labels.

1. Have students write cladogram at the top of the paper and copy the branched diagram shown in the text.

2. On the smaller pieces of paper, have students copy the terms shown on the cladogram in the text.

3. Students should work in pairs to say and correctly place the characteristics and animals on the branched diagram.

4. Students may want to affix the labels to the paper and add drawings to their cladogram. Within each student pair, have students explain their cladogram to the class.

Teacher Demo

Classification Tools Ask students to name six different animals. List them on the board.

1. Draw a branched diagram on the board or chart paper. Think aloud as you identify characteristics common to all the animals.

2. Think aloud as you note a characteristic that all but one animal has (such as has gills). Add the characteristic to the branched diagram and place the animal missing that characteristic to its left.

3. Continue the demo until all the animals are placed on the cladogram.

Classification Tools

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Suppose you go fishing and catch a fish you don’t recognize. How could you figure out what type of fish you have caught? There are several tools you can use to identify organisms.

Dichotomous Keys

 

A dichotomous key is a series of descriptions arranged in pairs that leads the user to the identification of an unknown organism. The chosen description leads to either another pair of statements or the identification of the organism. Choices continue until the organism is identified.

 

The dichotomous key shown in Figure 3 identifies several species of fish.

Figure 3 Dichotomous keys include a series of questions to identify organisms.

 

Cladograms

A family tree shows the relationships among family members, including common ancestors. Biologists use a similar diagram, called a cladogram. A cladogram is a branched diagram that shows the relationships among organisms, including common ancestors. A cladogram, as shown in Figure 4, has a series of branches. Notice that each branch follows a new characteristic.

 

Each characteristic is observed in all the species to its right. For example, the salamander, lizard, hamster, and chimpanzee have lungs, but the salmon does not. Therefore, they are more closely related to each other than they are to the salmon.

Figure 4 A cladogram shows relationships among species. In this cladogram, salamanders are more closely related to lizards than they are to hamsters.

 

 

1 NOTE

How would you name an unknown organism?

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Class: 20 min

Purpose
To use binomial nomenclature for identifying unknown organisms to understand better how scientists use this method to identify and organize living things.

Before You Begin
Review the section on binomial nomenclature to be certain students understand how to use it to identify specific organisms.

Guide the Investigation
1. Have students read the phrases to clarify meanings of phrases. Ask students to give oral definitions of the phrases to determine their understanding of the meanings of the phrases. Students may work in pairs if you feel some will benefit from teamwork.

2. Make sure students understand that the genus name of living things determines the characteristics that a group of organisms have in common. (e.g., All dogs have four legs, fur, sharp teeth, strong jaws, fused wrist bones, and so on.) They should also understand that the species name describes specific characteristics of one type of organism from that group. (e.g., A collie has different characteristics from those of a beagle.)

3. Allow students to observe and describe characteristics for the organisms illustrated in the lab.

4. Have students complete the binomial nomenclature chart by creating genus and species names from the list of phrases below the pictures.

5. Students who are having trouble with the chart could work in pairs.

MiniLab: How would you name an unknown organism?

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Assign scientific names to four unknown alien organisms from a newly discovered planet.

1. Use the table to assign scientific names to identify each alien.

 

Analyze and Conclude

1. Explain why you chose the two-word names for each organism.

Answers should indicate that students based the names on each organism’s characteristics.

2. Compare your names to those of a classmate. Explain any differences.

Accept any reasonable responses.

3. Key Concept Discuss how two-word scientific names help scientists identify and organize living
                            things.

Because each organism is given a specific two-word scientific name, scientists worldwide will use the same name for that organism and classify it the same way.

Lesson Review

Visual Summary

All organisms are classified into one of three domains: Bacteria, Archaea, or Eukarya.

Every organism has a unique species name.

Shin Yoshino/Minden Pictures/Getty Images

A dichotomous key helps to identify an unknown organism through a series of paired descriptions.

 

What do you think NOW?

You first read the statements below at the beginning of the lesson.

1. A dichotomous key can be used to identify an unknown organism.

2. Physical similarities are the only traits used to classify organisms.
    Did you change your mind about whether you agree or disagree with the statements?
    Rewrite any false statements to make them true.

Lesson Assessment

Use Vocabulary

1. A naming system that gives every organism a two-word name is __________.

binomial nomenclature

2. Use the term dichotomous key in a sentence.

Sample answer: I used a dichotomous key to identify two different trees at my school.

3. Organisms of the same __________ are able to produce fertile offspring.

species

     Understand Key Concepts

4. Describe how you write a scientific name.

The first word in a scientific name is the genus of the organism. The second word might describe the organism’s appearance or its behavior.

5. Compare the data available today on how to classify things with the data available during     
    Aristotle’s time.

Physical and molecular data are available today that were not available during Aristotle’s time.

6. Which is NOT used to classify organisms?

         A.ancestry

         B.habitat

         C.age of the organism

         D.molecular evidence

7. Which shows the correct order for the classification of species?

         A.domain, kingdom, class, order, phylum, family, genus, species

         B.domain, kingdom, phylum, class, order, family, genus, species

         C.domain, kingdom, phylum, class, order, family, species, genus

         D.domain, kingdom, phylum, order, class, family, genus, species

8. The organism shown below belongs in which kingdom?

Creatas/PunchStock

         A.Animalia

         B.Archaea

         C.Bacteria

         D.Plantae

Interpret Graphics

9. Organize Information Copy and fill in the graphic organizer below to show how organisms are classified.

From top to bottom: domain, kingdom, phylum, class, order, family, genus, species

Critical Thinking

10. Suggest a reason scientists might consider changing the current classification system.

Answers will vary. Accept any reasonable response.

11. Evaluate the importance of scientific names.

Scientific names are important because people worldwide use the same name for the same species.

12. Explain how using a dichotomous key can help you identify an organism.

Student answers will vary. Answers should reflect students’ understanding of what a dichotomous key is and how to use one to identify an object/organism.

13. Describe how the branches on a cladogram show the relationships among organisms.

Each branch of a cladogram follows a different characteristic. All organisms to the right of that branch have that characteristic, but all organisms to the left of that branch do not have the characteristic.

14. Assess the effect of molecular evidence on the classification of organisms.

Molecular evidence has given scientists a new way to compare and classify organisms. This has led to changes in the classification system, such as the addition of domains.

15. The photo below shows living and nonliving things. How would you classify the living things    
      by domain and kingdom?

Vaughn Fleming/Garden Picture Library/Photolibrary

domain Eukarya, kingdom Plantae

Writing in Science

16. Write a five-sentence paragraph explaining the importance of scientific names. Be sure to include
        a topic sentence and a concluding sentence in your paragraph.

Answers will vary. Sample answer: Scientific names allow persons across the world to communicate about an organism. The scientific name of an organism is specific to that organism. A common name may be used to refer to many similar organisms, or an organism may have more than one common name. The scientific name avoids any confusion that may come from using the common name.

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