15..2 Classifying Organisms
Look around you. What types of living things do you see? You probably see plants and
animals. What would you see if you could shrink down to the size of a cell? At this size, you
might see dust mites crawling across the floor (Figure 15.4). You would definitely see bacteria,
a microscopic life form that lives just about everywhere. With so many organisms in the world,
how do scientists keep track of them all? In this section, you will learn how scientists classify
organisms into major groups called domains and kingdoms.
Why do we classify things?
A trip to the
grocery store
Ryan wanted to cook chicken and rice for his family. He looked in the
cupboard and found that they were out of rice. He had to get some quick, so
he ran to the grocery store. The huge store contained thousands of products.
He located the aisle marked "pasta, beans, and rice" and quickly found
exactly what he was looking for.
The Grocery.stores.are organized so you can find things easily. Products are
importance of grouped in aisles according to their similarities. You wouldn't look in the
classification
dairy aisle if you wanted to find canned pineapple! Likewise, scientists
classify organisms by grouping them according to similarities. Taxonomy
is the study of classification. The diagram below shows some questions
scientists ask before classifying organisms into major groups.
1. Prokaryotic or
eukaryotic cells?
2. Unicellular
or multicellular?
6~12;~Q;.I,<:i¢ntifytb€!basicchi:ltaj
:i!i~'I~r:ii:
~~t;:',i'
:-:~~{h/r~·>~:
::~&~·;::~~t/~~:~;./~:~:;:
:~.---:-...:~;::',:.. .~~:.;..~ ';~;..'..j
tlfi
f.
taxonomy - the study of classification
3. Autotroph
or heterotroph?
•
"
.
-
<~
!"~~~~~i;~Ti!~~~'1
(prg~qi,~pjs,i.§·~.iYIR.~pint().cUr(entIY
:tt~?~~rl;~~'~:R~;~ln~
•• ....< ..; .
.
.
,
Figure 15.4: Dust mites are tiny
organisms that live in your home.
Reading 15.2 Classifying Organisms
m, i
371
.j
~
1f
¥
Domains and the prokaryotic groups
Domains A domain is the highest level of classification of organisms. In 1990,
Carl Woese, an American biologist, introduced a three-domain system of
classification that is widely accepted by scientists. There are two domains
for prokaryotes: archaea, which are ancient prokaryotes; and bacteria, which
are the more recent and common prokaryotes. Eukaryotes are organized
into the domain Eukarya. The eukarya are discussed on the next pages.
domain- the highest level of
classification of organisms
Domain The archaea are a domain of unicellular, prokaryotic organisms that
Archaea
reproduce asexually. Some members of this domain are heterotrophs while
others are autotrophs. In the past, the archaea were considered to be an
unusual group of bacteria and were classified in the same group. After
further study, scientists found that archaea's chemistry is distinctly different
from other bacteria and developed the three-domain system of classification
used today. Archaea were first thought to live only in extreme environments,
such as hot springs and undersea volcanic vents. But recently they have been
found in soil, swamps, and the ocean. Figure 15.5 shows a type of archaea
found in a hot spring.
Domain The bacteria are a domain of unicellular, prokaryotic organisms that
Bacteria
reproduce sexually and have a different chemistry than the archaea. Some
bacteria are heterotrophs while others are autotrophs. Cyanobacteria are
examples of photosynthetic (use photosynthesis to make their own food)
bacteria (Figure 15.6). Bacteria are often described according to the shape
of their cells. Rod-shaped bacteria are called bacilli. Ball-shaped bacteria
are called cocci. Spiral-shaped bacteria are called spirilla.
Bacilli
Cocci
Spirilla
Figure 15.6: Cyanobacteria are
photosynthetic bacteria. They rnakel
own food using photosynthesIs.
r'
: ,'I
Kingdoms and the domain Eukarya
1.(
,:
Kingdoms
Taxonomy changes as scientists gather more information about organisms.
In one classification scheme, the domain Eukarya is divided into four
kingdoms. A kingdom is the level of classification below the level of
domain. The kingdoms of the domain Eukarya include Protista, Fungi,
Plantae, and Animalia. All organisms in the domain Eukarya have
eukaryotic cells.
It
I~
kingdom - the level of classification
of organisms below the level
of domain
iI
The diagram below summarizes the domains and kingdoms of organisms.
The Domains of Life
Domain EUKARYA
I
\
i
I
II
Kingdom Fungi
Kingdom Protista
Dorriain BACTERIA
.
-.:-.:
II
i ~.
:t,
I
l.
_ -~~-:~i~~m?pt8fitae~~~"~-~'.
.ca"
')
.. _
O'!l'u.
~."
.
j<
_
i','!<
~~
_.
_,J.~!;i
"Kjn~dOm
'n
,-"
.
J
Ani~alia
.,~ .•_
Reading 15.2 Classifying Organisms
•.
,.._- •.. ),l!'
373
Kingdoms Protista and Fungi
Kingdom
Protista
Members of the kingdom Protista are called protists. Figure 15.7 shows the
major characteristics of protists. Protists are mostly unicellular, though there
are some simple, multicellular protists. Some protists are autotrophic while
others are heterotrophic. Protists have both asexual and sexual reproduction.
Because the different groups of protists have so little in common, their
taxonomy is still changing. Today, some scientists do not recognize protists-as a kingdom and instead classify them into other groups. The diagram
below shows some representative protists.
A
~
',j,1 .~_?:,'.>.:::,,::;.:"
/
Euglanoids
;"',>.i1" ~/' ::;~j;~~'f''':'
Watermolds
Ciliates
Slime molds
Chrysophytes
These are charaaeristks
the kingdom Protista.
Figure 15.7:
Kingdom Fungi
Kingdom Fungi includes the fungi, mushrooms, molds, and yeasts. You may
have seen members of this kingdom growing on rotting logs in the woods.
Fungi are important because they break down rotting things and return the
nutrients to the soil. Fungi have eukaryotic cells and most (except yeasts)
are multicellular. They are heterotrophs and get their energy by breaking
down and absorbing dead organisms like rotting logs. Fungi use both
asexual and sexual reproduction. Figure 15.8 shows the major characteristics
of fungi.
These are cnaractemi!
the kingdom Fungi.
Figure 15.8:
()f
-
----
_I;)";",ft,,[
:/:~~jh:}t.~;t~~:~~~7~~~~~~~
f'
! .~
Plantae
..
. r:
'.
Kingdoms Plantae and Anlmalla
Kingdom
1;
i'.·,!
11' ~
j • .!
The kingdom Plantae is made up of multicellular organisms with eukaryotic
cells. Using photosynthesis, plants convert energy from the Sun and store it
in the form of food molecules. A product of this process is the oxygen you
breathe. Plants reproduce through sexual reproduction. Examples of plants
include mosses, ferns, trees, and flowering plants. Figure 15.9 shows the
major characteristics of plants.
tr
»,
Figure 15.9: These are characteristics of
the kingdom PJantae.
Kingdom
Animalia
Like plants, animals are multicellular organisms with eukaryotic cells.
Unlike plants, members of the kingdom Animalia need to eat other
organisms to get their energy-they are heterotrophic. Animals reproduce
through sexual reproduction. Beetles, worms, snakes, and birds are animals.
You are also an animal. Figure 15.10 shows the major characteristics of
animals,
Ahim~ir.'~';:"
-;'.,\"
;
o
••
have eukaryotic cells.
I....
o
••
are multicellular.
IIlf
~~
-;:'
';.1:
Fig ure 15.10: These
of kingdom Anlmalla.
are characteristics
Reading 15.2 Classifying Organisms
"
375
Classification groups
~
-
....
-...
~
I.Uniceliular
or Multicellular
I
type of Cells
Domain Archaea
Prokaryotic cells
Unicellular
Prokaryotic cells
Unicellular
Autotroph or Heterotroph
,r:K.l.:r:.TIJ.tYo
Some are autotrophsand
some are heterotrophs
~~
./"'~'"
Domain Bacteria
Some are autotrophsand
some are heterotrophs
Asexual reproduci
~
~
-:
,;-~
.Domain Eukarya
-":"
'.
.',
Some
Kingdom Protista
Eukaryotlocells
SOfu~:aieurlicelltJlar'artcl
some
nluJticelluar
Kingdom Fungi
Eukaryotic cells
Some are unicellular and
some are multicellular
Eukaryotic cells
All multicellular
ate
376
:"".",',.':
.. :~
autotrophsand
Asexual and
sexual reproductl
Heterotroph
Asexual and
sexual reprodu
Autotroph
Sexual
. .
""
are
somear~ih~terotrophs
.j)';,j'{
..
,-,-
Eu)<atyolicpells
Unit 5 Organisms and Ecosystems
",'
__ '
All multicellular
~
-
,,<: ...,,:,-,>:",,',;-:"',.:,',,",'
H€teli!>l:jiop'h
,...;...;.
Sexual