CLASSIFICATION-How are Living Things Classified?
(Reading)
Classification
When similar items are placed together, they are being classified.
Organisms also are classified into groups. Early classifications of
organisms included grouping plants that were used in medicines.
Animals were often classified by human traits. For example, lions
were classified as courageous animals and owls were classified as
wise.
More than two thousand years ago, Aristotle, a Greek, decided that any
organism could be classified as either a plant or an animal. Then he
broke these two groups into smaller groups. For example, his groups
included animals that had hair and animals that did not have hair, and
animals with and without blood.
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Who was Carolus Linnaeus?
In the late 1700s, Carolus Linnaeus, a Swedish naturalist, developed a
new system of grouping organisms. His system was based on
organisms with similar structures. For example, plants that had a
similar flower structure were grouped together. His system was
accepted and used by most other scientists.
What classification do modern scientists use?
Modern scientists also use similarities in structure to classify
organisms. They also use similarities in both external and internal
features. For example, scientists use the number of chromosomes in
cells to understand which organisms may be genetically related to each
other.
In addition, scientists study fossils, hereditary information, and early
stages of development. Scientists use the information to determine an
organism’s phylogeny. Phylogeny (fi LAH juh nee) is the organism’s
evolutionary history. This tells how the organism has changed over
time. It is the basis for the classification of many organisms.
How are organisms grouped?
A classification system commonly used today groups organisms into
six kingdoms. A kingdom is the first and largest category. Kingdoms
are divided into smaller groups. The smallest classification is a
species. Organisms in the same species can mate and produce fertile
offspring. The figure below shows how a bottle-nosed dolphin can be
classified.
Why are scientific names used?
Two-word scientific names are used for four reasons.
They help avoid mistakes.
Animals with similar evolutionary history are classified together.
Scientific names give descriptive information about the species.
Scientific names allow information about organisms to be
organized easily and efficiently.
Tools for Identifying Organisms
Tools used to identify organisms include field guides and dichotomous
(di KAH tuh mus) keys. Field guides include descriptions and pictures
of organisms. They give information about where each organism lives.
You can use a field guide to identify species from around the world.
Scientific Names
If scientists used only common names of organisms, it would be
confusing. For example, a jellyfish is neither a fish nor jelly. A sea lion
is more closely related to a seal than a lion. To avoid confusion,
scientists use a naming system developed by Linnaeus when referring
to a particular species. Each species has a unique, two-word scientific
name.
What is binomial nomenclature?
The two-word naming system used to name organisms is called
binomial nomenclature (bi NOH mee ul · NOH mun klay chur). The
first word of the two-word name identifies the genus of the organism.
A genus is a group of similar species. The second word of the name
might tell you something about the organism. It might tell what it
looks like or where it is found.
What are dichotomous keys?
A dichotomous key is a detailed list of identifying characteristics that
includes scientific names. The keys are set up in steps. Each step has
two descriptive statements, such as hair or no hair. You can use a
dichotomous key, such as the one below, to identify and name a
species.
CLASSIFICATION-How are Living Things Classified?
(Questions)
I. Use the reading to answer the following questions.
1. Describe the system used by Linnaeus to group organisms.
_________________________________________________________
_________________________________________________________
(paragraph(s) _______________________)
2. Explain What can you learn from the phylogeny of an organism?
_________________________________________________________
_________________________________________________________
(paragraph(s) _______________________)
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3. Classify Name of the kingdom and species of the bottle-nosed
dolphin.
Kingdom: _____________________________________________
Species: ______________________________________________
(paragraph(s) _______________________)
4. Explain What does the first word in an organism’s binomial
nomenclature indicate?
_________________________________________________________
(paragraph(s) _______________________)
5. List two tools that can be used to identify organisms.
_________________________________________________________
_________________________________________________________
(paragraph(s) _______________________)
6. Identify the mouse that has a mostly dark, hairy tail and large ears.
___________________________________________________
V. Label the groups used to classify organisms from least specific
to most specific. Use the word bank to complete the diagram.
class genus order species family kingdom phylum
II. Use the reading to find the term (vocabulary word) that
matches each definition.
first and largest category
1.
used to classify organisms.
evolutionary history of an
2.
organism.
group of similar species.
3.
two-word scientific naming
system.
4.
III. Contrast historic classification systems. Identify the categories
or criteria used in each system to classify living things.
Early
Aristotle
Linnaeus
classification
VI. Summarize binomial nomenclature. Complete the sentences.
1. The first word of an organism’s scientific name is its __________.
2. The second word might __________________________________
________________________________________________________.
Categories
or
Criteria
VII. Identify four reasons the system of binomial nomenclature is
useful.
1. ____________________________________________________
____________________________________________________
2. ____________________________________________________
IV. List the 6 types of information that modern scientists use to
determine an organism’s phylogeny.
1.
4.
2.
5.
3.
6.
____________________________________________________
3. ____________________________________________________
____________________________________________________
4. ____________________________________________________
____________________________________________________