Student
text pages
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518–521
SECTION
17.1
The Linnaean System
of Classification
SC.912.L.15.4
KEY CONCEPT Organisms can be classified based on physical similarities.
Linnaeus developed the scientific naming system
still used today.
Do you know what an Irish daisy is? What about a lion’s tooth flower? A
dandelion? Irish daisy, lion’s tooth, and dandelion are all common
names for the same flower. You can imagine how confusing it could be
for scientists to try to talk about a particular organism if everyone has a
different name for it.
In the 1750s, the Swedish botanist Carolus Linnaeus developed a system for classifying* and naming living things.
Linnaeus’ system gave naturalists a common language, which
made it easier for them to talk about their findings with one
another.
Taxonomy
Taxonomy is the science of naming and classifying organisms.
Linnaean taxonomy classifies organisms based on their physical similarities. A group of organisms in a classification system
is called a taxon (plural, taxa). The species is the basic taxon of
the Linnaean system. A species is a group of organisms that can
breed and produce offspring that can reproduce. With a few
changes, the Linnaean system of naming is still used today.
Cardinal
The cardinal is a species of bird.
A species is the basic taxon of
the Linnean system.
Scientific Names
Binomial nomenclature (by-NOH-mee-uhl NOH-muhnKLAY-chuhr) is a system that gives each species a two-part
scientific name using Latin words. The first part of the name
is the genus. The second part describes the species.
• Genus A genus (plural, genera) includes one or more
species that are thought to be closely related. For example,
the genus Quercus includes more than 500 species of oak
trees. Genus names always begin with a capital letter.
They are written in italics or underlined.
* ACADEMIC VOCABULARY
classifying organizing into groups
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McDougal Littell Biology
VISUAL VOCAB
Binomial nomenclature is a standard
naming system that gives each species
a two-part name using Latin words.
two
name
naming
system
bi nomial nomen clature
(1) Genus (2) species
• Species descriptor The second part of the name describes the
species. The species descriptor is also written in italics or underlined.
It is written in lowercase letters. Quercus alba is the scientific name
for white oak trees.
The species descriptor is never written alone because the same
descriptor may be used for many different genera. For example,
Quercus alba is the scientific name for white oak trees and Tyto alba is
the scientific name for barn owls. The descriptor alba means “white.”
Alone, alba does not refer to any particular species.
There can be many different common names for one particular
species. Irish daisy, lion’s tooth, and dandelion are all common names.
But there is only one scientific name for this plant: Taraxacum officinale.
Not only can there be many names for an organism in one language, but
there are many more names for an organism in different languages.
Scientific names help scientists around the world talk about particular
organisms without confusion.
Find the scientific name for dandelion in the paragraph above.
Circle the genus. Draw a box around the species descriptor.
Linnaeus’ classification system has seven levels.
The Linnaean system of classification has seven levels: kingdom,
phylum (plural, phyla), class, order, family, genus, and species.
The most general level is kingdom. A kingdom contains one
or more phyla. A phylum contains one or more classes,
and so on.
Underline the seven levels of Linnaeus’
classification system.
kingdom
phylum
class
order
family
genus
species
The Linnaean classification system has
limitations.
Linnaeus’ system is based on physical similarities between
organisms. However, organisms that are physically similar
are not always closely related. Recall that unrelated species can
evolve similar traits through convergent evolution, as they
adapt to similar environments.
Each level in the Linnaean system of classification is nested, or
included, in the level above it.
Interactive Reader
285
Today, scientists use molecular and genetic research to help classify
living things. Genetic similarities give strong evidence that organisms are
related. Genetic information has resulted in some organisms getting
reclassified into different groups.
What
is one limitation
of Linnaeus’
classification
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What is one
limitation
of Linnaeus’
classification
system?
8=:8@
system?
17.1
Mark It Up
Vocabulary Check
taxonomy
taxon
binomial nomenclature
genus
Fill in the blanks with the correct term
from the list above.
Go back and highlight
each sentence that
has a vocabulary
word in bold.
1. Binomial nomenclature has two parts: the
and the species descriptor.
2.
is the science of naming and classifying
organisms.
3. A
is a group of organisms in a classification system, such as a species or a genus.
17.1
The Big Picture
4. What is one reason that scientific names, instead of common names,
help scientists to communicate about organisms?
5. What are the seven levels of classification, from biggest to smallest?
6. Linnaeus’ classification system is based on physical similarities. What
type of information has been used more recently to determine relationships between organisms?
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Visual Connection
See classification
system in student
text, pg. 520