Classification of Life
Introduction
When you see an organism that you have never seen
before, you probably put it into a group without even
thinking. If it is green and leafy, you probably call it a plant. If
it is long and slithers, you probably call it as a snake. How do
you make these decisions? You look at the physical features
of the organism and think about what it has in common with
other organisms.
Classification is the arrangement of organisms into orderly groups based on shared characteristics.
Because there are millions of different organisms on the planet, scientists have devised a system for sorting
organisms into groups. Once sorted, the organisms are given a scientific name based on the groups they are a
part of. Scientists classify, or put into categories, living things by their physical features, but also by how
closely related they are. Lions and tigers look like each other more than they look like bears, but are lions and
tigers related? Evolutionarily speaking, yes. Lions and tigers both evolved from a common ancestor. So it turns
out that the two cats are actually more closely related to each other than to bears. How an organism looks
and how it is related to other organisms determines how it is classified.
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Why Classify?
Classification makes it easier for scientists to answer the following questions:
1. How many known species are there?
2. What are the characteristics of each species?
3. What are the relationships between species?
Levels of Classification
There are eight levels of classification: domain, kingdom,
phylum, class, order, family, genus, and species. The level with the
largest number of organisms in it is the domain, whereas the
species level consists of a single type of organism.
The diagram to the right illustrates the classification categories for
organisms, with the broadest category (domain) at the top, and
the most specific category (species) at the bottom.
History of Classification
People have been concerned with classifying organisms for
thousands of years. Over 2,000 years ago, a Greek philosopher, Aristotle,
developed a classification system that divided living things into several
groups that we still use today, including mammals, insects, and reptiles.
Carolus Linnaeus (CARE-ole-us lin-AY-us) was a Swedish physician and
botanist who lived from 1707 to 1778. Linnaeus built on Aristotle's work
to create his own classification system. He invented the way we name
organisms today, with each organism having a two-word name. Linnaeus
is considered the inventor of modern taxonomy, the science of
identifying, classifying, and naming organisms.
Defining a Species
Even though naming species is straightforward, deciding if two organisms are the same species can
sometimes be difficult. Linnaeus defined each species by the distinctive physical characteristics shared by the
organisms. But two members of the same species may look quite different. For example, people from different
parts of the world sometimes look very different, but we are all the same species. So how is a species defined?
A species is defined as a group of similar individuals that can interbreed with one another and produce fertile
offspring. A species does not produce fertile offspring with other species.
Binomial Nomenclature (also known as Scientific Naming)
Linnaeus developed binomial nomenclature, a way to give a scientific name to every organism. In this
system, each organism receives a two-part name in which the first word is the genus (a group of species), and
the second word refers to one species in that genus. For example, the coyote's scientific name is Canis
latrans. Latrans is the species and Canis is the genus, a larger group that includes dogs, wolves, and other dog157
like animals. The names may seem strange, but the names are written in Latin or Greek and are italicized (if
typed) or underlined (if hand-written). The first word is always capitalized and the second is lowercase.
Scientific names are always the same for a specific organism, no matter how many common names it might
have. Scientific names are important because scientists all around the world know organisms by their
scientific names; it is a common language for them.
Dichotomous Keys
Dichotomous keys are guides that aid
in the classification of organisms. They consist
of several pairs of descriptive statements.
When one of the two choices is selected, the
reader is led to another set of descriptive
statements. Once all statements have been
selected, the scientific name of the organism is
provided. To the right is an example using
sharks.
Review of “Classification Basics” Reading
1. Why is classification useful?
2. As you move down the levels of classification, what happens to the number of organisms in each group?
3. Describe the formatting rules for a scientific name.
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Classification Notes: Guided Reading
Introduction

__________________________________ is the arrangement of organisms into orderly groups based
on shared characteristics.
Why Classify?

Classifying organisms answers the following questions:
o How many ___________ _____________ are there?
o What are the _______________________ of each species?
o What are the _______________________ between species?
Levels of Classification

There are _____ levels of classification:

The _________________ category is at the top and the most _____________ category is at the
bottom.
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History of Classification

The first classification system was created by ____________ over 2,000 years ago.

___________________________ _______________________________ invented the way we name
organisms today, with each organism having a two-word name.

__________________ is the science of identifying, classifying, and naming organisms.
Defining a Species

A _____________ is a group of similar individuals that can interbreed with one another and produce
fertile offspring.
Binomial Nomenclature (aka Scientific Naming)

Linnaeus developed _______________________ _____________________, which is a way to give a
scientific name to every organism.
o In this system, the first word is the _____________ and the second is the ____________.
o The names are written in ______________ or ______________.
o The names are also italicized if ______________ or underlined if _________________________.
o The first word is always _______________________ and the second is _______________________.

______________________ names are always the same for a specific organism, no matter how many
_________________ names it might have.

Scientific names allow scientists all around the word to communicate in a common
_______________________.
Dichotomous Keys

_____________________ __________ are guides that aid in the classification of organisms.

They consist of several _______ of descriptive statements that lead to the scientific name of the
organism.
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Dichotomous Pamishans
Help! Scientists have discovered quite a few new creatures on planet Pamishan. They need your help to identify and classify them.
Use the dichotomous key to identify these creatures.
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Pamishan Dichotomous Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
a. The creature has a large wide head...................................................................................... go to 2
b. The creature has a small narrow head................................................................................ go to 11
a. It has 3 eyes .......................................................................................................................... go to 3
b. It has 2 eyes .......................................................................................................................... go to 7
a. There is a star in the middle of its chest................................................................................ go to 4
b. There is no star in the middle of its chest ............................................................................ go to 6
a. The creature has hair spikes ........................................................................... Broadus hairytritops
b. The creature has no hair spikes............................................................................................. go to 5
a. The bottom of the creature is arch-shaped .................................................... Broadus staryarchus
b. The bottom of the creature is M-shaped ...................................................... Broadus staryemmus
a. The creature has an arch-shaped bottom .............................................................. Broadus archus
b. The creature has an M-shaped bottom.................................................................. Broadus tritops
a. The creature has hairy spikes ............................................................................................... go to 8
b. The creature has no spikes.................................................................................................. go to 10
a. There is a star in the middle of its body .......................................................... Broadus hairystarus
b. There is no star in the middle of its body ............................................................................. go to 9
a. The creature has an arch shaped bottom ............................................................... Broadus hairus
b. The creature has an M shaped bottom ......................................................... Broadus hairyemmus
a. The body is symmetrical ........................................................................................ Broadus emmus
b. The body is not symmetrical........................................................................... Broadus mismatchus
a. The creature has no antennae ............................................................................................ go to 12
b. The creature has antennae ................................................................................................ go to 14
a. There are spikes on the face ................................................................................. Narrowus wolfus
b. There are no spikes on the face ......................................................................................... go to 13
a. The creature has no spike anywhere .................................................................. Narrowus blankus
b. There are spikes on the right leg ................................................................. Narrowus starboardus
a. The creature has 2 eyes....................................................................................................... go to 15
b. The creature has 1 eye......................................................................................... Narrowus cyclops
a. The creature has a mouth................................................................................................... go to 16
b. The creature has no mouth................................................................................................. go to 17
a. There are spikes on the left leg ............................................................................. Narrowus portus
b. There are no spikes at all ................................................................................. Narrowus georginia
a. The creature has spikes ...................................................................................................... go to 18
b. The creature has no spikes .................................................................................. Narrowus plainus
a. There are spikes on the head ............................................................................................. go to 19
b. There are spikes on the right leg.................................................................... Narrowus montanian
a. There are spikes covering the face ....................................................................... Narrowus fuzzus
b. There are spikes only on the outside edge of head .......................................... Narrowus beardus
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Domains & Kingdoms
Domains
Domains are the largest level of classification, meaning they have the largest number of
organisms within them. There are three domains, each with its own set of characteristics.
 Archaea: To be in the domain Archaea, an
organism must be a prokaryote that lives in
extreme environments. This domain only has
one kingdom in it.
 Bacteria: To be in the domain Bacteria, an
organism must be a prokaryote that lives in
many different environments. This domain only
has one kingdom in it.
 Eukarya: To be in the domain Eukarya, an
organism must be a eukaryote. This domain has
four different kingdoms in it.
Kingdoms
There are six kingdoms that make up the second level of classification. To be part of each
kingdom, an organism must have a particular set of characteristics.
 Archaebacteria: Archaebacteria is the only kingdom within the Archaea domain.
Archaebacteria are prokaryotes, meaning that they are unicellular organisms without a nucleus
but with a cell wall. They have been on Earth for at least 3 billion years ("archae" means
ancient) and live in extreme environments, like deep sea vents or hot springs. Archaebacteria
can be producers (also called autotrophs) or decomposers (a type of heterotroph, which are
organisms that do not make their own food) and reproduce asexually.
 Eubacteria: Eubacteria is the only kingdom within the Bacteria domain. Eubacteria are another
type of prokaryote but they live in many different environments (even in human stomachs).
Apart from where they live, Eubacteria have exactly the same traits as Archaebacteria.
 Protista: Protista is one of four kingdoms within the Eukarya domain. Protists are a type of
eukaryote, which means their cells have a nucleus, and are mostly unicellular. Some of them
have a cell wall and they can be producers, consumers, or decomposers – meaning they can be
both autotrophs and heterotrophs. Some reproduce asexually, while others reproduce sexually
and they are mostly aquatic (water-dwelling).
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 Fungi: Fungi are another of the four kingdoms within the Eukarya domain. They are another
type of eukaryote and they are mostly multicellular. Like plants, they have cell walls but, unlike
plants, they are decomposers. Fungi reproduce both sexually and asexually and can live in
water or on land.
 Plantae: Plantae is the third of the four kingdoms within the Eukarya domain. They are
multicellular autotrophs, meaning they make their own food. Some reproduce sexually and
others reproduce asexually and they can live in water or on land.
 Animalia: Animalia is the last of the four kingdoms within the Eukarya domain. They are also
multicellular organisms but they are consumers, meaning they have to eat other organisms for
energy, and they do not have cell walls. They reproduce sexually and can live in water or on
land.
Eukaryotes
Prokaryotes
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Review of “Domains & Kingdoms” Reading
1. What is the main difference between Archaea and Bacteria?
2. What is the main difference between the domain Eukarya and the other two domains?
3. List three characteristics of each kingdom that you would use to separate it from the others.
A. Animalia
B. Plantae
C. Fungi
D. Protista
E. Eubacteria
F. Archaebacteria
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 Unicellular OR Multicellular
 Cells have a nucleus.
The system is continually modified throughout the
years – there used to be only FIVE kingdoms!
Each kingdom can be broken down even further
based on the characteristics of the organisms. For
example, Animalia is broken down into animals
with backbones and without backbones.
...which are then divided into smaller groups (called Kingdoms)...
...are divided into 3 large groups (called Domains)...
ALL LIVING THINGS
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Examples:
Habitat?
Producer, Consumer,
and/or Decomposer?
Heterotroph or
Autotroph?
Type of
Reproduction?
Have cell walls?
Unicellular or
Multicellular?
Eukaryotic or
Prokaryotic?
Kingdoms 
Domains 
Bacteria
Eubacteria
Archaea
Archaebacteria
Protista
Fungi
Eukarya
Plantae
Animalia
The 3 Domains & The 6 Kingdoms
Formative Assessment: Levels & Kingdoms
DIRECTIONS: List the levels of classification in order from BROADEST to MOST SPECIFIC.
DIRECTIONS: Match the kingdom name to its description.
WORD BANK: Animalia (A), Archaebacteria (AB), Eubacteria (E), Fungi (F), Plantae (PL), Protista (P)
_______ 1. I am so tiny that you need a microscope to see me. I only have one cell, which does not have a
nucleus. I reproduce asexually, basically cloning myself. I am living on your desk right now.
_______ 2. I can be big or small, but I always have many cells. All of my cells have a nucleus and I am a
heterotroph, so I can't make my own food. My relatives and I almost always reproduce sexually. My
cells lack cell walls.
_______ 3. I am a tiny organism and I live in a pond. My little body only has one cell, but I do have a nucleus. I
am a decomposer, but some of my relatives are producers and consumers.
_______ 4. Some people might think I'm a plant because I am eukaryotic and I have a cell wall, but I'm not.
Please don't think I'm gross just because I'm a decomposer. I am multicellular, but some of my
relatives are unicellular.
_______ 5. My relatives existed when Earth was young. We may be really teeny-tiny, but we are strong. I may
not have a nucleus, but I can survive in boiling water or deep under the ocean near a volcanic vent.
_______ 6. I am eukaryotic. I have millions of cells in my body, which all have cell walls. I am an autotroph (I
use sunlight to make my own food). Some of my relatives reproduce asexually, but I reproduce
sexually.
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