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18 –1 Finding Order in Diversity
Section 18–1
1 FOCUS
F
or more than 3.5 billion years, life on Earth has been constantly changing. Natural selection and other processes have
led to a staggering diversity of organisms. A tropical rain forest,
for example, may support thousands of species per acre. Recall
that a species is a population of organisms that share similar
characteristics and can breed with one another and produce
fertile offspring. Biologists have identified and named about
1.5 million species so far. They estimate that anywhere between
2 and 100 million additional species have yet to be discovered.
Objectives
Key Concepts
• How are living things
organized for study?
• What is binomial
nomenclature?
• What is Linnaeus’s system of
classification?
18.1.1 Explain how living things
are organized for study.
18.1.2 Describe binomial nomenclature.
18.1.3 Explain Linnaeus’s system of
classification.
Vocabulary
Why Classify?
To study this great diversity of organisms, biologists must give
each organism a name. Biologists must also attempt to organize
living things into groups that have biological meaning.
To
study the diversity of life, biologists use a classification
system to name organisms and group them in a logical
manner.
In the discipline known as taxonomy, scientists classify
organisms and assign each organism a universally accepted
name. One example appears in Figure 18 –1. By using a scientific name, biologists can be certain that everyone is discussing
the same organism. When taxonomists classify organisms, they
organize them into groups that have biological significance.
When you hear the word “bird,” for example, you immediately
form a mental picture of the organism being discussed—a flying
animal that has feathers. But science often requires smaller
categories as well as larger, more general categories. In a good
system of classification, organisms placed into a particular
group are more similar to one another than they are to organisms in other groups.
You use classification systems also, for example, when you
refer to “teachers” or “mechanics,” or more specifically,
“biology teachers” or “auto mechanics.” Such
a process, like scientific classification,
uses accepted names and common
criteria to group things.
taxonomy
binomial nomenclature
genus
taxon
family
order
class
phylum
kingdom
Reading Strategy:
Building Vocabulary
As you read about the seven
categories established by
Linnaeus, list those categories in
order, starting with the smallest
group. Then, create a memory
aid to help you remember them.
Figure 18 –1 Depending on where
you live, you might recognize this as a
mountain lion, a puma, a cougar, or a
panther—all of which are common names
for the same animal. The scientific name for this
animal is Felis concolor.
To avoid the confusion caused by regional names, biologists use a
classification system to group organisms in a
logical manner and to assign names.
One example of a memory aid to
help students remember the seven
taxonomic categories is: Sam gave
Fred one copper padlock key.
2 INSTRUCT
SECTION RESOURCES
Technology:
• Teaching Resources, Lesson Plan 18–1,
Adapted Section Summary 18–1, Adapted
Sav18–1,
Worksheets 18–1, Section Summary
e
e
Worksheets 18–1, Section Review 18–1
• Reading and Study Workbook A, Section 18–1
• Adapted Reading and Study Workbook B,
Section 18–1
• Investigations in Forensics, Investigation 5
• iText, Section 18–1
• Transparencies Plus, Section 18–1
r
Print:
Tim
Explain how the Vocabulary terms
are related. State that in biology the
term taxonomy refers to the classification of organisms and that binomial
nomenclature refers to the system of
assigning names developed by
Linnaeus. In Linnaeus’s system,
organisms are classified into a hierarchy of categories. Ask: Which of
the Vocabulary terms refer to categories in Linnaeus’s system? (Genus,
family, order, class, phylum, and kingdom)
Reading Strategy
왔
왘
Vocabulary Preview
Why Classify?
Demonstration
Introduce students to dichotomous
classification with a quick demonstration. First, have all the students stand
up. Then, as you read aloud each of
the following physical characteristics,
have students without the characteristic sit down: over 5 feet tall, brown
eyes, female, left-handed. By the
time you have named all the characteristics, all or nearly all of the
students are likely to be sitting down.
Point out that with each characteristic you named, the remaining
group became narrower. Conclude
that grouping organisms based on
comparing characteristics makes it
easier to study the diversity of life.
Classification
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Assigning Scientific Names
18–1 (continued)
By the eighteenth century, European scientists recognized that
referring to organisms by common names was confusing.
Common names vary among languages and even among regions
within a single country. The animal you saw in Figure 18–1, for
example, can be called a cougar, a puma, a panther, or a mountain lion. Furthermore, different species sometimes share a
single common name. In the United Kingdom, the word
buzzard refers to a hawk, whereas in many parts of the
United States, buzzard refers to a vulture. To eliminate such
confusion, scientists agreed to use a single name for each
species. Because eighteenth-century scientists understood Latin
and Greek, they used those languages for scientific names. This
practice is still followed today in naming newly discovered
species, such as the barking deer in Figure 18 –2.
Assigning Scientific
Names
Build Science Skills
Applying Concepts Challenge students to brainstorm other examples
of species with more than one common name. (Possible examples include
the woodchuck, which is also called
ground hog, and the yellow poplar
tree, which is also called tulip tree.)
Use Community Resources
Display several field guides for your
region. Explain how field guides are
used to help identify the species of a
plant or animal based on physical
characteristics similar to the ones that
were used in early efforts at naming.
For example, a field guide to trees
identifies holly trees based on such
characteristics as whether the leaf
edges are scalloped and whether
they are hairy on their undersides.
Encourage interested students to borrow the field guides and use them to
identify flora or fauna in the community. Give students a chance to share
their observations with the class.
왖
Figure 18–2 The problem of
naming organisms efficiently continues to challenge biologists as they
discover new species. This barking
deer was recently discovered near the
border of Laos and Vietnam. Its
scientific name, which is based on
Latin, is Muntiacus muntjak.
In
binomial nomenclature, each
animal is assigned a two-part
scientific name.
N S TA
For: Links on
classification
Visit: www.SciLinks.org
Web Code: cbn-5181
N S TA
Download a worksheet
on classification for students to
complete, and find additional
teacher support from NSTA
SciLinks.
A biped has two feet.
Binomial and nomenclature are
built from some familiar roots. Bi- is
Latin for “two.” Nomen- is Latin for
“name.” So binomial nomenclature
means a two-name system of
assigning names. If pedis is Latin
for “of the foot,” how many feet
does a biped have?
Early Efforts at Naming Organisms The first attempts at
standard scientific names often described the physical characteristics of a species in great detail. As a result, these names could be
twenty words long! For example, the English translation of the
scientific name of a particular tree might be “Oak with deeply
divided leaves that have no hairs on their undersides and no teeth
around their edges.” This system of naming had another major
drawback. It was difficult to standardize the names of organisms
because different scientists described different characteristics.
Binomial Nomenclature A major step was taken by
Carolus Linnaeus, shown in Figure 18 –3, a Swedish botanist
who lived during the eighteenth century. He developed a
two-word naming system called binomial nomenclature
(by-NOH-mee-ul NOH-mun-klay-chur). This system is still in
use today.
In binomial nomenclature, each species is
assigned a two-part scientific name. The scientific name is
always written in italics. The first word is capitalized, and the
second word is lowercased.
For example, the grizzly bear shown in Figure 18–4 is called
Ursus arctos. The first part of the scientific name—in this case,
Ursus—is the genus to which the organism belongs. A genus
(JEE-nus; plural: genera, JEN-ur-uh) is a group of closely
related species. The genus Ursus contains five other kinds of
bears, including Ursus maritimus, the polar bear.
The second part of a scientific name—in this case, arctos or
maritimus—is unique to each species within the genus. Often,
this part of the name is a Latinized description of some important trait of the organism or an indication of where the organism lives. The Latin word maritimus, referring to the sea, comes
from the fact that polar bears often live on pack ice that floats in
the sea.
Do Ursus arctos and Ursus maritimus belong to the
same species? To the same genus?
SUPPORT FOR ENGLISH LANGUAGE LEARNERS
Comprehension: Prior Knowledge
Beginning To introduce binomial nomenclature, hand out a graphic organizer with four
columns. The far left column should be labeled
Organism, and each cell in the left column
should have a picture of a common organism.
The next column should be labeled Scientific
Name, and the cells should be filled with the
scientific names of the organisms in the left
column. The next two columns should be
448
Chapter 18
completed by ESL students paired with Englishproficient students. The pairs should fill in the
English names of the organisms and the names
of the organisms in the ESL students’ native
languages.
Intermediate Ask students to list, in English,
several organisms with which they are familiar.
The students should work with Englishproficient students to research and write the
scientific names of these organisms.
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Linnaeus’s System of
Classification
Linnaeus’s System of Classification
Linnaeus’s classification system is hierarchical; that is, it consists of levels.
Linnaeus’s hierarchical system of
classification includes seven levels. They are—from
smallest to largest—species, genus, family, order, class,
phylum, and kingdom. In taxonomic nomenclature, or naming system, each of those levels is called a taxon (plural: taxa),
or taxonomic category.
The two smallest categories, genus and species, were discussed in the example of the bears. The giant panda, shown in
Figure 18–4, resembles the grizzly bear and the polar bear.
However, it differs enough from them and other species in the
genus Ursus that it is placed in its own genus, Ailuropoda.
Genera that share many characteristics, such as Ursus and
Ailuropoda, are grouped in a larger category, the family —in
this case, Ursidae. These bears, together with six other families of animals, such as dogs (Canidae) and cats (Felidae), are
grouped together in the order Carnivora. An order is a broad
taxonomic category composed of similar families. The next
larger category, the class, is composed of similar orders. For
example, order Carnivora is placed in the class Mammalia,
which includes animals that are warm-blooded, have body hair,
and produce milk for their young.
Several different classes make up a phylum (FY-lum; plural:
phyla). A phylum includes many different organisms that nevertheless share important characteristics. The class Mammalia is
grouped with birds (class Aves), reptiles (class Reptilia), amphibians (class Amphibia), and all classes of fishes into the phylum
Chordata. All these organisms share important features of their
body plan and internal functions. Finally, all animals are placed
in the kingdom Animalia. The kingdom is the largest and most
inclusive of Linnaeus’s taxonomic categories. Linnaeus named
two kingdoms, Animalia and Plantae. You can see the seven
taxonomic levels in Figure 18 –5 on the next page.
Grizzly Bear
Ursus arctos
Polar Bear
Ursus maritimus
Address Misconceptions
왖 Figure 18 –3 Carolus Linnaeus
(1707–1778) brought order to the
process of naming species and
classifying them into groups.
Evaluating Why do biologists
consider Linnaeus’s system an improvement over earlier systems?
Figure 18 – 4 The grizzly bear,
Ursus arctos, and the polar bear,
Ursus maritimus, are classified as
different species in the same genus,
Ursus. The giant panda is placed in a
separate genus. Inferring What do
the scientific names of the polar and
grizzly bears tell you about their
similarity to each other?
Demonstration
Demonstrate how Linnaeus’s system
of classification consists of organisms
that are increasingly similar as you go
from the level of kingdom to the
level of species. Show students pictures of a domestic dog, wolf, fox,
and mountain lion. Ask: What are
some ways these animals are similar, and what are some ways they
are different? (Accept all reasonable
responses.) Then, explain that the
mountain lion, fox, wolf, and dog are
classified together at the level of
order (Carnivora); the fox, wolf, and
dog, at the level of family (Canidae);
and the wolf and dog, together at
the level of genus (Canis).
Giant Panda
Ailuropoda melanoleuca
FACTS AND FIGURES
Why pandas are carnivores
Most people are familiar with the bamboo-eating
habits of the giant panda. In fact, pandas depend
so much on bamboo in their diet that they have
evolved a sixth front “toe” to help them grasp
and eat their favorite food. If pandas are herbivores, why are they classified in the order
Carnivora, as shown in Figure 18–5? The answer
lies in their evolutionary past. Like other bears,
their most recent ancestor was a carnivorous
Students might think that different
breeds of dogs, cats, and other
domesticated animals are different
species. Explain that the term breed
refers to a domesticated variety of an
organism that is a subgroup of a
species. For example, dogs of different breeds, no matter how dissimilar
they look, all belong to the species
Canis familiaris. Because they are
members of the same species, they
can mate and produce fertile
offspring.
Answers to . . .
bearlike animal. All of today’s bears, however,
have evolved into omnivores, meaning they will
eat almost anything, including fruit, seeds, honey,
insects, fish, and meat. Pandas have evolved to
depend on a narrower omnivorous diet than
most other bears, depending as they do almost
exclusively on bamboo. However, they may feed
on gardens, crops, and even chickens if their
usual food supply is threatened.
They do not belong to
the same species, but they do belong to
the same genus.
Figure 18 –3 Because it provides a
brief and unique name for each species
Figure 18 –4 The shared genus
name Ursus indicates that the two
species are in the same genus and thus
are closely related.
Classification
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Grizzly bear
18–1 (continued)
Black bear
Giant panda
Red fox
Abert
squirrel
Coral
snake
Sea star
Build Science Skills
Classifying Have the class work in
groups to develop a system, similar
to the Linnaean system, to classify a
collection that includes a hair clip,
bobby pin, safety pin, straight pin,
screw, nail, paper clip, and staple. (All
are fasteners, and subsets might be
classified on the basis of other shared
characteristics. For example, hair clips
and bobby pins are fasteners of hair,
screws and nails are fasteners of wood,
and paper clips and staples are fasteners of paper. Other characteristics that
might be used include sharpness,
shape, or color.) Have groups share
their systems. Then, ask: How is the
classification affected by the characteristics selected? (Different objects
are grouped together if different characteristics are selected.)
3 ASSESS
Evaluate Understanding
Have students write a paragraph
explaining why it is important to
classify the diversity of living things.
KINGDOM Animalia
PHYLUM Chordata
CLASS Mammalia
ORDER Carnivora
FAMILY Ursidae
왘 Figure 18–5
Linnaeus’s
hierarchical system of classification
uses seven taxonomic categories.
This illustration shows how a grizzly
bear, Ursus arctos, is grouped within
each taxonomic category. Only
some representative species are
illustrated for each category above
the species level.
GENUS Ursus
SPECIES Ursus arctos
Reteach
Call on students to name the categories of the Linnaean classification
system in order from smallest to
largest. Write each term on the
board. Have students brainstorm
examples of each category, such as
Chordata for phylum and Mammalia
for class.
Possible paragraphs might describe
how students use the raters’ classification system to choose movies
or an alphabetical classification system to find names in a phone
book. Encourage students to think
of classification systems they use
that are obviously hierarchical like
the Linnaean system, such as the
Library of Congress classification
system they use to find a nonfiction book in the library.
If your class subscribes to the iText,
use it to review the Key Concepts in
Section 18–1.
450
Chapter 18
18–1 Section Assessment
1.
Key Concept How are
living things organized for study?
2.
Key Concept Describe the
system for naming species that
Linnaeus developed.
3.
Key Concept What are the
seven taxonomic categories of
Linnaeus’s classification system?
Rank these taxa in hierarchical
order, beginning with the largest
level and ending with the smallest.
4. Why do scientists avoid using
common names when discussing
organisms?
5. What is binomial nomenclature?
6. Critical Thinking Applying
Concepts Look at Figure 18 –5
above. Are foxes more closely
related to sea stars or to snakes?
Explain.
Explanatory Paragraph
Think of a classification system that you use in everyday
life, and then write a paragraph explaining how the
classification system organizes
objects or other things. Hint:
Before you write, make a diagram that shows the organization of the classification
system.
18 –1 Section Assessment
1. Biologists use a classification system to
name organisms with a universally accepted
name. They also group organisms in a logical manner. Organisms placed into a
particular group are more similar to one
another than they are to organisms in other
groups.
2. Each species is assigned a two-part scientific
name.
3. Kingdom, phylum, class, order, family, genus,
species
4. Because common names vary among languages and even among regions within a
single country
5. A two-word naming system
6. They are more closely related to snakes,
because they are in the same phylum.