Download Six Kingdoms

S E C T I O N
11.1
Six Kingdoms
E X P E C TAT I O N S
Describe characteristics of
representative organisms.
Compare the structure and
function of prokaryotic and
eukaryotic cells.
Classify organisms living in
your neighbourhood.
Figure 11.1 Is this an animal
or a plant? How would you
decide?
Everyone classifies. You classify your books by
grouping them in a particular order on a shelf. You
classify your clothes by putting them in particular
drawers or hanging them up in the closet. The
groups we make and the names we give the groups
reflect patterns in the world around us. Some
groups are clearly defined. For example, “people
under 18 years of age” and “people 18 years of age
or older.” Other groups are more fuzzy. For
example, “people who speak French” and “people
who don’t speak French.” In which group would
you place people who know a few French phrases
but are not fluent? One of the most interesting
challenges for biologists is finding a way to classify
Earth’s millions of species.
If you were given the task of separating all
organisms into categories, how could you begin?
What characteristics would you use to classify
living things? Among the most obvious are the
characteristics that separate animals and plants.
Over two thousand years ago, the Greek philosopher
Aristotle divided all living things into these two
large groups, Plantae and Animalia. He called each
group a kingdom, a term still used today.
Classifying organisms is not always
straightforward. You could start with the fact that
most animals are motile (have a method of
locomotion) and ingest the food they have obtained.
Most plants, on the other hand, are non-motile and
obtain their food through photosynthesis. However,
some organisms, such as the ones shown in
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MHR • Diversity of Living Things
Figure 11.1, appear to have characteristics of both
plants and animals. For example, sponges and
corals, like those in Figure 11.2, spend most of
their lives fixed in one place like plants. Unlike
plants, however, sponges and corals do not make
their own food through photosynthesis.
Figure 11.2 Some organisms, such as these sponges and
the coral reef that they live on, can be difficult to classify
using obvious characteristics such as the ability to move.
PAUSE
RECORD
Classification can be much more difficult than you might
think at first glance. Think about organisms you have seen
or read about. Make a list of ten organisms that you feel
would be easy to classify, and a list of ten organisms that
would be more difficult. Consider your lists, and write a
paragraph summarizing your thoughts.
BIO
FACT
The small tropical country of Costa Rica (in Central
America) has 200 known mammal species and more than
850 known species of birds. By comparison, Canada —
which is 185 times larger — is home to only 147 known
species of land mammals and 394 known species of birds.
Micro-organisms
Classifying organisms became more difficult after
the microscope was invented in the seventeenth
century. The new magnifying tool revealed a
previously unknown world of living things. Some
microscopic organisms have methods of
locomotion and capture their food, as animals do.
Some carry out photosynthesis, as plants do.
However, some micro-organisms have
characteristics of both animals and plants. For
example, euglena are common single-celled
organisms that swim by means of a flagellum but
also carry out photosynthesis.
In 1866, the German biologist Ernst Haeckel
proposed classifying micro-organisms that are
MINI
neither animals nor plants in a third kingdom,
which he named Protista. As biologists learned
more about the structure and way of life of
different organisms, they added more kingdoms to
the classification system. Fungi, such as
mushrooms and moulds, were originally included
in the plant kingdom. However, fungi do not carry
out photosynthesis. They obtain food by absorbing
materials into their bodies. They are classified in a
fourth kingdom, named Fungi.
Bacteria consist of very small cells that differ in
appearance from the cells of animals, plants,
protists, and fungi. Bacteria lack a nucleus and
other organelles, and are able to grow and obtain
energy in a wide range of environments. They are
classified in a fifth kingdom, named Bacteria. Some
textbooks refer to this kingdom as Eubacteria,
Prokaryotae, or Monera.
During the 1990s, there was growing interest in
certain types of bacteria found living in extreme
environments, such as salt lakes or hot, acidic
springs. Detailed studies showed that these
organisms have unique structures and mechanisms
that allow them to live in conditions where no
other organisms — including other bacteria — can
survive. The new data led scientists to rename
these micro-organisms and to reclassify them in a
sixth kingdom, named Archaea. Some sources may
refer to these organisms as Archaebacteria. These
six kingdoms are shown in Figure 11.3 on the
next page.
LAB
Organizing Life
How many different organisms live in your neighbourhood?
In this activity, you will make an inventory of and classify
local species. Make a list of all the different organisms you
observe during a 15-minute walk around your school or
home. Be as specific as possible (for example, robin, not
bird; earthworm, not worm). You should have at least
20 species in your list. Organize your list into groups based
on the similarities and differences you observe among the
various types of organisms. Begin by choosing a
characteristic that lets you divide your list of organisms into
two groups: one group that has the characteristic and one
group that does not (for example, wings and no wings). List
the organisms in each group on a separate sheet of paper.
Record the group characteristic in your notebook. Next,
decide if you can subdivide one or both of your groups
using another characteristic. If so, list the organisms in your
new subgroups on separate sheets of paper. Continue
subdividing your lists until you cannot see another way to
do so. Record the classification characteristics you use in
your notebook.
Analyze
1. What characteristics did you use to define your groups
of organisms? How many different subgroups did you
make? Suggest a way in which you could improve the
classification of your groups.
2. Exchange your collection of groups with a partner. Can
you discover the characteristics used by your partner to
create each group? Record the characteristics you
think your partner used. How accurately did your
partner identify the characteristics of each group you
created? Explain.
Patterns of Life • MHR
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Mammals
Birds and
Reptiles
Amphibians
and Fishes
Flowering
Plants
Starfishes
Conifers
Ferns
PLANTS
ANIMALS
Arthropods
Mosses
Mollusks
and Worms
FUNGI
PROTISTS
Jellyfishes
and Sponges
ARCHEA
BACTERIA
Cenozoic
Mesozoic
Paleozoic
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Eras: shown in millions of years ago
Paleozoic
544
544
Figure 11.3 This fan diagram represents the six kingdoms
of life extending out over the geologic time scale. The origin
of life is shown at the base during the Precambrian Era, and
present-day species are represented along the outer edge
of the fan. Each kingdom is represented by a different colour.
MINI
Mesozoic
Cenozoic
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PLAY
The incredible diversity of living things can be difficult to
appreciate with only a few examples. Go to your Electronic
Learning Partner for videos showing the biodiversity present
in different ecosystems.
LAB
Classifying to Kingdom
Kingdoms describe very large groups of organisms. Usually,
you need more than one single characteristic in order to
identify which kingdom an organism belongs to. The best
way to classify organisms is to study as many of their
different characteristics as possible.
Your teacher will provide you with samples of two
organisms you have probably never seen before. Your task
is to classify each by kingdom. Observe the samples both
with the naked eye and under a microscope. Record as
many characteristics of each specimen as possible. Review
your list and determine the kingdom to which each
organism belongs.
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MHR • Diversity of Living Things
Analyze
1. What characteristics of each organism helped you
make your decision? Explain why these characteristics
were helpful.
2. Your teacher will provide you with other examples of
organisms in different kingdoms. List characteristics
that you could use to classify these organisms just by
looking at them. Would you need more information?
Explain your answer.
3. What characteristics on your list are present in more
than one kingdom? Are there any characteristics that
were not helpful in your classification scheme? List the
characteristics that you did not find helpful. Discuss
why you feel they are not helpful.
Prokaryotes and Eukaryotes
Table 11.1
The study of cells is an important first step in
understanding the diversity of life. Biologists
recognize two basic types of cells based on
differences in their size, structure, and other
characteristics, shown in Figure 11.4. Recall from
Chapter 2 that cells lacking a true nucleus and
most other types of organelles are called
prokaryotic cells (pro means before, karyon means
nucleus). Bacteria and archaea, the smallest and
simplest type of cells, are referred to as
prokaryotes. The cells of other organisms are larger
and have a more complex internal structure. They
contain nuclei and other types of membrane-bound
organelles. Such cells are called eukaryotic cells
(eu means true), and organisms with these cells are
called eukaryotes. Table 11.1 summarizes some of
the differences between these cells.
Math
Two types of cells
Prokaryotes
Eukaryotes
bacteria, archaea
protists, plants, fungi, animals
small (1–10 µm)
large (100–1000 µm)
DNA circular, not bounded by
membrane
DNA in nucleus bounded by
membrane
genome made up of a single
chromosome
genome made up of several
chromosomes
cell division not by mitosis and
meiosis
cell division by mitosis and
meiosis
asexual reproduction common
sexual reproduction common
multicellular forms rare
most forms are multicellular
mitochondria and other
membrane-bound organelles absent
mitochondria and other organelles
present
many are anaerobic
(do not require oxygen)
most are aerobic (require oxygen)
LINK
Draw a graph or pie chart illustrating the proportions of the
following relationships:
• First prokaryotes appear 3.5 billion years ago.
• First eukaryotes appear 1.5 billion years ago.
• First multicellular organisms appear 700 million years ago.
For what percentage of time that life has existed on Earth did it
consist only of prokaryotes?
For what percentage of time that life has existed on Earth did it
consist only of unicellular organisms?
Fossil evidence shows that the first forms of life
were prokaryotic organisms similar in appearance
to bacteria. Remains of these single-celled
organisms have been found in rocks dated at
3.5 billion years old. The first eukaryotes did
not appear until about 2 billion years later
(1.5 billion years ago). The first multicellular forms
of life appeared only 700 million years ago. In
other words, unicellular organisms have a much
longer history than do multicellular organisms
such as plants, animals, and fungi.
nucleus
plasma membrane
B prokaryotic cell
DNA
plasma membrane
cell wall
flagellum
chromosomes
A eukaryotic cell
capsule
Figure 11.4 Plants, animal, fungi, and protists are referred to as eukaryotes.
They contain eukaryotic cells like the one shown in (A). Bacteria and archaea are
referred to as prokaryotes. They are prokaryotic cells like the one shown in (B).
Patterns of Life • MHR
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The Three Domains
Although today’s prokaryotes look little different
from the earliest forms of life, recent research has
shown that living prokaryotes are far more diverse
than anyone had previously suspected. Details of
the molecular biology of bacteria and archaea,
especially studies of their RNA structure, show that
they are as different from each other as either is
from eukaryotes. This led to these three groups
being organized into a new level of classification
above kingdoms, known as domains. The three
domains — Bacteria, Archaea, and Eukarya — are
shown in Figure 11.5.
Within the Domain Eukarya, the greatest
biological diversity occurs within the Kingdom
Protista. For example, there is a much greater
genetic difference between some species of protists
than there is between, for example, corn and
humans. Protists have lived on Earth for a much
longer time than plants and animals, which has
given this group more opportunity to change and
diversify. Many scientists believe the Kingdom
Protista should be divided into several different
kingdoms, but no one new system of classification
for it has been generally accepted.
Domain Bacteria
Domain Archaea
Domain Eukarya
Kingdom
Bacteria
Kingdom
Archaea
Kingdoms
Protista, Fungi,
Plantae, Animalia
Figure 11.5 Kingdoms are grouped into three domains based on the types of cells
the organisms in each kingdom have. Note that Eukarya are linked more closely to
Archaea than to Bacteria.
SECTION
1.
K/U List examples of classification systems you use
every day.
2.
K/U Would a group identified as “flying animals” be
useful to a biologist? Explain why or why not.
3.
K/U Why should all scientists use the same scheme
to classify living things?
4.
C Create a concept organizer to show the different
domains and kingdoms. Include the appropriate
characteristics that define each grouping in list form.
5.
I You have discovered an unknown organism while
on a field trip. You think it is a new species of protist.
How could you test to identify this species as a
protist? What data would you need to have to
classify it in the Kingdom Protista?
6.
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REVIEW
K/U Plants and fungi have been classified in the
same kingdom in the past. Most scientists today
classify fungi in their own kingdom. Explain how
these two different classification schemes are
supported by data.
MHR • Diversity of Living Things
7.
I You discover an unusual organism growing on the
bark of a dying tree. Later, in the laboratory, you look
at some of its cells under a microscope. It is a
multicellular organism with eukaryotic cells, but no
chloroplasts. To what kingdom does it belong?
8.
C Using the information contained in Table 11.1 and
Figure 11.4, create a handout contrasting prokaryotic
and eukaryotic cells. If you were to teach this material
to students in an earlier grade, what information
would be the most important to teach them the
basic differences between the two cell types?
9.
MC When a new development is being proposed,
the developer usually has to submit an Environmental
Impact Assessment. This is a scientific study that
outlines the effect of the development on the local
environment. Explain how a knowledge of
classification would be necessary to prepare your
Environmental Impact Assessment. Why would you
need to know about the different kingdoms?