section the classification of living things...

1 1 . 3S E C T I O N The Classification of Living Things

390 MHR • Diversity of Living Things

EXPECTAT IONS

Define the fundamentalprinciples of taxonomy.

Demonstrate the usefulness of the system of scientificnomenclature.

Construct a key for theidentification of differentorganisms.

Figure 11.11 Features such aspetals are used to classify flowering plants into differentgroups or taxa.

When detectives ask an eyewitness to describe agetaway vehicle, the more specific the descriptionthe witness gives, the more likely it is that thedetectives will be able to identify the car. Themodel, colour, and year of the car all narrow downthe search. But there may still be hundreds orthousands of vehicles that fit this description. Ofcourse, the license plate number is the bestevidence of all. Together with the other details, itaccurately describes one particular car.

In the same way, biologists need specific detailsto identify organisms. For example, if you ask azoologist to help you identify a species of bird, it isnot very useful to describe the bird as small andbrown. Many dozens of species of small brownbirds live in Canada. One purpose of aclassification system, therefore, is to allow theaccurate identification of a particular organism.

The practice of classifying organisms is knownas taxonomy (taxis means arrangement and nomosmeans law). The system of taxonomy used byscientists today was founded nearly 300 years agoby a Swedish botanist named Carolus Linnaeus(1707–1778). Linnaeus used simple physicalcharacteristics to identify different species andorganize them into groups. For example, he basedhis classification of flowering plants, like the oneshown in Figure 11.11, on the number andarrangement of features such as petals and stamens.Using this system, people could accurately identify

an organism by comparing its appearance against achecklist of characteristics.

During the 1700s, explorers from Europe werediscovering more and more of the world’s richdiversity of plants and animals — including manyspecies Europeans had never seen before. Thanksto the work of Linnaeus, they were able to classifythese unknown organisms into groups of similarspecies. Linnaeus’s system was so easy to use thatit quickly became popular.

Naming OrganismsBiologists still use Linnaeus’s method of namingeach species using two words, such as Felisdomesticus (the house cat). Many of these namesare based on Latin or Greek words because whenLinnaeus developed his system of classification inthe 1700s, these classical languages were thecommon languages of science. When scientists findand describe new species, they are required to givethe species a Latin scientific name. These namesoften reflect characteristics of the organisms, or inother cases, the names are given to honour a fellowscientist or historical figure. Latin continues to beused for these new names.

391Patterns of Life • MHR

Hierarchy of GroupsAs members of the animal kingdom, the bee, shark,horse, dog, and oyster shown in Figure 11.12 havecertain things in common. On the other hand, theseanimals are obviously not very much alike. Thereare different degrees of similarity among animals.For example, a horse is more like a dog than like ashark (horses and dogs are mammals; sharks arefish). However a horse is more like a shark thanlike an oyster (horses and sharks are vertebrates;oysters are invertebrates). To distinguish suchdifferent degrees of similarity, each kingdom issubdivided several times into a series ofprogressively smaller groups. Each group is calleda taxon (plural taxa).

Kingdoms are the largest and most general taxa— they include many thousands of species. Speciesare the smallest taxa — they include only a singletype of organism. Between kingdoms and species,organisms are classified into a minimum of fiveother taxa, which form a hierarchy of groups. Table 11.2 lists the names of these taxa and givesan example of each. In some systems, additionaltaxa are used to help subdivide large groups. Forexample, subphylum is an added taxon betweenphylum and class.

You can see from Table 11.2 that a species isclassified in a particular taxon at every level of thehierarchy. For example, a bobcat is a member of theKingdom Animalia, the phylum Chordata, the classMammalia, and so on. As you move down thetable, each taxon contains fewer species. As well,the smaller the taxon, the more similar theorganisms within it. The taxon species includesmembers that resemble each other so closely thatthey can interbreed and produce fertile offspring.

To learn about the genetic basis for differences amongspecies, turn to Chapter 6, Section 6.1.

REWIND

Taxon Example Organisms included in this taxon

Kingdom

Phylum

Class

Order

Family

Genus

Species

Species

Animalia

Chordata

Mammalia

Carnivora

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

Table 11.2An example of hierarchical classification

Over 75% of named living species belong to the phylumArthropoda, which includes such diverse organisms aslobsters, crabs, shrimp, barnacles, sow bugs, scorpions,spiders, mites, millipedes, and insects. The insects are byfar the most abundant arthropods. What physicalcharacteristic(s) do you think all arthropods have incommon? List your ideas and explain them briefly.

PAUSE RECORD

Figure 11.12 A bee, shark, horse, dog, and oyster are all members of the animal kingdom.

S K I L L F O C U S

Performing and recording

Analyzing and interpreting

Communicating results

I n v e s t i g a t i o n 1 1 • A


Pre-lab Questions

What characteristics do all insects have incommon?

Name two characteristics that scientists use totell different insects apart.

Problem

How do you make a dichotomous key?

Prediction

Predict which characteristics of insects will bemost useful in creating an identification key.

Materials

illustration of 18 beetles sample dichotomous keyspaper pencil

Procedure

1. Copy the diagram of a dichotomous treeshown here onto a separate piece of paper.

2. Study the illustration of 18 beetles shownon the next page.

3. Select one characteristic and sort the beetlesinto two groups based on whether they havethe characteristic or not.

4. List each beetle’s number under eitherGroup 1 or Group 2 on your diagram.

5. Record the characteristic that identifies each group.

6. Select another characteristic of eachsubgroup, and repeat steps 4 and 5 for thenext level down on your diagram.

7. Continue to subdivide the groups until youhave 18 groups with one beetle in each.

All beetles

group 1

group 2

group 3

group 4

group 7

group 8

group 9

group 10

group 11

group 12

group 13

group 14

group 5

group 6

Creating a Dichotomous KeyIf you find an insect you have never seen before, how could youdiscover its identity? Many field guides help you match up thecharacteristics of your specimen with those of similar organisms usinga dichotomous key. This identification key uses a series of pairedcomparisons to sort organisms into smaller and smaller groups. In thisinvestigation, you will learn how to make your own keys toidentification.


8. Using the characteristics shown on yourdiagram, construct a dichotomous key thatsomeone could use to identify any beetlefrom the original large group. To do this,create a series of numbered steps with thefirst step showing the first characteristic youused. At each step, offer two choices forclassifying the beetle based on a singlecharacteristic. For example, you may haveused the characteristic “antennae longerthan front legs” as your first dividingcharacteristic. Your first numbered step inyour key would be (1a) antennae longer thanfront legs or (1b) antennae not longer thanfront legs. Use the sample keys provided byyour teacher to help you.

9. Exchange your key with a partner. Use yourpartner’s key to classify a beetle, and recordall the characteristics of the species youchose.

Post-lab Questions

1. Did your partner produce a dichotomous keyidentical to yours? Explain why or why not.

2. Which beetle characteristics were not usefulfor creating your key? Explain why not.

Conclude and Apply

3. Why does a key offer two choices at eachstep and not more than two?

4. In your own words, define a dichotomouskey.

Exploring Further

5. Your teacher will provide you with severaldifferent “mystery” beetles. Use yourdichotomous key and see if you can identifywhat species the beetles are. You may beunable to completely identify your beetleusing your key. If this is the case, how farcould you go with your key? Visit the libraryor the Internet and get a field guide tobeetles. Use this to identify the mysterybeetles. What characteristics would youhave needed in your key in order to fullyidentify them?

1

Variegated mud-loving beetle

2

Mycetaeidbeetle

3

Apricot borer

4

Water tiger

5

Predaceousdiving beetle

6

Crawlingwater beetle

7

Flatheadapple borer

8

Red-neckedcane borer

9

Cucumbersnout beetle

10

Whirligig beetle

11

Ironclad beetle

12

Broad-hornedflour beetle

13

Red flour beetle

14

Blindant-beetle

15

False wirewormbeetle

16

White-markedspider beetle

17

Montereycyprus beetle

18

Drug storebeetle

T H I N K I N G L A B

Classifying DinnerBackgroundFor dinner one evening, you are served a seafood stewcontaining lobster, squid, mussels, and two types of oysters.In the same way that the marine organisms are mixed uptogether in your bowl, the various names of the taxa thatidentify these five species are mixed up in the chart to theright. In this lab, you will redraw the chart and place eachorganism in its proper taxon at each level of the hierarchy.

You Try It1. Draw a chart with six columns and seven rows. At the

top of the first column, write “Taxon.” At the top of eachof the other columns, write the common name of oneorganism from the chart. Label the rows: Phylum,Class, Order, Family, Genus, and Species, matching theorder on the chart. Use reference books or the Internetto gather enough information to classify each organismcorrectly at each taxon level.

2. According to your classification scheme, which is theonly taxon level in which all five organisms have a different name? Which order name is found in both theArthropoda and Mollusca phyla (plural of phylum)?What does this name mean? Which two genera (pluralof genus) have species with names containing the sameword? What does this word mean?

3. Which two organisms are most closely related to eachother? Give a reason for your answer. Which organismis least closely related to the other four? Give a reasonfor your answer.

Commonname

Market squid, American lobster, blue mussel, Virginia oyster, European oyster

Phylum

Class

Order

Family

Genus

Species

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


The system of using a two-word name for eachspecies is called binomial nomenclature. The firstword is the name of the genus (plural genera) inwhich the organism is classified. The first letter ofthis name is capitalized. Because a genus maycontain more than one species, there may beseveral species with the same first name. Forexample, the genus Canis includes Canis lupus

(wolf), Canis latrans (coyote), and Canis familiaris(domestic dog). The fact that these three animalshave the same first name tells you that they are allin the same genus of dog-like animals and are verysimilar to one another. The second word in thename identifies the particular species. Thus, eachspecies name has a unique two-word combination.


Common NamesYou may wonder what is wrong with referring toorganisms by their everyday names, such as “cat.”Common names are not precise. The animal youthink of when you hear the word “cat” may not bethe same animal being described. There aredifferent species of cats, such as wild cats and ring-tailed cats. Animals such as lions and tigers arealso called cats. In addition, people in differentregions may use different common names to referto the same species. For example, puma, cougar,and mountain lion are three different commonnames 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 ideasabout the basic characteristics of an organism andthe group in which it should be classified. Forexample, 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 ashellfish and a starfish than between a catfish andyou. In fact, biologists place each of these fivemembers of the animal kingdom in a separatephylum (Figure 11.13).

Figure 11.13 The common names of all these animalsinclude 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

shellfish: phylum MolluscaA starfish: phylum EchinodermataB

jellyfish: phylum CnidariaC crayfish: phylum ArthropodaD

catfish: phylum ChordataE


S E C T I O N R E V I E W

1. List two reasons why the system of binomial nomenclature is useful.

2. Cats, goldfish, and humans are in the samephylum. What characteristics do they have in common? What characteristics place cats andhumans in a different order from goldfish?

3. Based on your own knowledge, place the following species into three different phyla: ant, crow,spider, turtle, salmon, snail, octopus.

4. 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.

5. Referring to the table shown here, which two animals are most closely related? Explain your answer.

6. The information in this 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.

7. What kind of an animal is Myotis myotis? How doyou know? Use the table shown here to help you.

8. Using the information contained in the tableshown here, create a display showing the relationships of the organisms. You may draw them,create a flow chart or a concept map, or you mayeven create a key.

9. There is a growing concern worldwide about thenumbers of species that are going extinct.Conservation organizations work to protect endangered species, however, there may be disagreement about what exactly a “species” is. Howcan naming an organism influence our attitudesabout that organism? For example, is a fish morelikely to be protected if it is a known endangeredspecies, or if it is newly discovered and different fromall known species of fish? How can a name influenceour feelings about a particular organism? Discuss thistopic and write a short essay about your ideas.

You have just learned about how scientists name andclassify organisms. You will be picking an endangeredspecies to study for your Unit 4 Issue Analysis. Does thespecies that you are considering have a common name?What are the organisms’ names in binomialnomenclature? Make sure you are considering organismsbased on their proper Latin names, not the commonnames that might be confusing.

UNIT ISSUE PREP

Organism House cat Dog

Kingdom

Phylum

Class

Order

Family

Genus

Species

Animalia

Chordata

Mammalia

Carnivora

Felidae

Felix

domesticus

Animalia

Chordata

Mammalia

Carnivora

Canidae

Canis

familiaris

Coyote

Animalia

Chordata

Mammalia

Carnivora

Canidae

Canis

latrans

Skunk

Animalia

Chordata

Mammalia

Carnivora

Mustelidae

Mephitis

mephitis

Brown bat

Animalia

Chordata

Mammalia

Chiroptera

Vespertilionidae

Myotis

lucifugus

Prayingmantis

Animalia

Arthropoda

Insecta

Mantodea

Mantidae

Stagmomantis

carolina

MC

C

I

I

I

I

I

K/U

K/U

The same common name may be used for differentspecies. For example, the bird called a robin inCanada is a different species from the bird called arobin in Great Britain (Figure 11.14).

Figure 11.14 Bird A is called a robin in Canada. Bird B, adifferent species, is called a robin in Great Britain.

A B

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