Video Transcript
In this video, we will learn to
describe the characteristics common to organisms in the kingdom Monera. We will learn about the differences
between eubacteria and archaea. And then we’ll practice classifying
organisms based on what we’ve learnt.
A kingdom is a very general
classification containing many different species. However, all organisms within a
particular kingdom have some traits in common. Kingdom Monera was originally
created to classify organisms which are prokaryotes. The main difference between
prokaryotic cells and eukaryotic cells is that prokaryotic cells do not contain a
nucleus. In eukaryotic cells, the genetic
material, or DNA, is in several long strands called chromosomes. And the chromosomes are stored and
protected within a nucleus.
In contrast, prokaryotic cells have
their genetic material in a chromosomal loop. And this loop of DNA is suspended
in the cytoplasm of the cell. In addition to not possessing a
nucleus, all prokaryotes reproduce asexually through a process called binary
fission. Prokaryotic organisms are also all
unicellular, although some of them can link together into strands or form
colonies. The organisms within kingdom Monera
can be further classified based on other traits into various phyla. These phyla can be further divided
into classes, classes into orders, orders into families, families into genera, and
genera into individual species. Remember that all of the members of
kingdom Monera possess the traits that we already described because they’re all
prokaryotes.
Let’s look at some additional
characteristics within kingdom Monera. The word part “karyote” means
kernel or nucleus, and the prefix pro- in this word means before. In contrast, the eu- in eukaryote
means true. Prokaryotic organisms evolved on
Earth before eukaryotic organisms. Some students find it helpful to
remember that pro- means no nucleus. In addition to not possessing a
nucleus, prokaryotic cells also do not possess other membrane-bound organelles, such
as mitochondria. Organisms within kingdom Monera may
be autotrophs, heterotrophs, or a mixture of both.
The difference between autotrophs
and heterotrophs is how they get the nutrients that they need to produce cellular
energy. Heterotrophic organisms must absorb
organic matter or consume other organisms in order to get the nutrients that they
need. On the other hand, autotrophic
organisms convert inorganic materials into the nutrients that they need to produce
cellular energy. They can do this using a process
called photosynthesis, which utilizes the energy found in sunlight, or through
chemosynthesis, which uses other sources of energy, such as heat. Auto- is a word part that means
self, which can help you remember that autotrophs make nutrients by themselves.
Another feature of prokaryotic
cells is that they possess a cell wall. The chemicals found in the cell
walls of different organisms is sometimes used as a key to their classification. Members of the plant kingdom have
cell walls made of cellulose, and members of the fungus kingdom have cell walls made
of chitin. But what about the cell walls of
monerans? Well, some monerans have a cell
wall made of a chemical called peptidoglycan, and some do not. For this reason and several others,
the moneran kingdom has more recently been divided into two separate kingdoms,
Bacteria and Archaea.
Archaea and bacteria have different
evolutionary histories and relationships, which give them different characteristics,
even though they’re both types of prokaryotes. Bacteria are sometimes called
eubacteria, which means true bacteria. These are the types of prokaryotes
that you’re most likely already familiar with. They exist everywhere and even
sometimes cause infections and illness. Archaea is a word that means old,
and they’re also sometimes referred to as archaebacteria. Archaebacteria got this name
because they were first found living in extreme environments similar to those
thought to have existed on Earth long, long ago. We call these organisms
extremophiles.
While archaea may most commonly be
found in environments like thermal vents, hot springs, or stomach acid, which has an
extremely low pH, scientists have since learnt that they also exist all throughout
nature. The cell walls of bacterial cells
are made of peptidoglycan, while the cell walls of archaea are made of other related
molecules. Archaea also differ from bacteria
in the structure of their RNA as well as certain aspects of their genetic
makeup.
Now that we’ve learnt about kingdom
Monera, what a prokaryote is, and the difference between bacteria and archaea, let’s
try a practice question.
Which of the following is a
characteristic of an organism belonging to kingdom Monera? (A) Most of these organisms are
large and multicellular. (B) The cells of these organisms
contain a cellulose cell wall. (C) These organisms only reproduce
sexually. Or (D) the cells of these organisms
do not contain a membrane-bound nucleus.
In order to answer this question,
we’ll recall what we know about the characteristics of the five kingdoms of
life. And then we’ll use this information
to determine which of the answer choices is specific to kingdom Monera. The American botanist Robert
Whittaker is credited with developing the five-kingdom system. The five kingdoms into which he
divided all living organisms are Monera, Plant, Animal, Fungus, and Protist.
The main difference that sets
members of kingdom Monera apart from the other four is that all monerans are
prokaryotic organisms, meaning that their cells do not possess a nucleus or other
membrane-bound organelles. All of the organisms in the other
four kingdoms of life are eukaryotic, meaning that their cells possess a nucleus in
which the genetic material, or DNA, is stored. If you’re able to remember that
monerans are prokaryotic and that pro- means no nucleus, then you have enough
information to answer this question. But we’ll investigate further and
determine why each of the other answer choices is incorrect.
All prokaryotic organisms are
unicellular, although some join together to form strands or colonies. This rules out the answer choice
that says these organisms are large and multicellular. The cell walls of monerans are made
of peptidoglycan or other similar molecules. The cell walls of plant cells are
made of cellulose, and the cell walls of fungal cells are made of chitin. So, we know that organisms
belonging to kingdom Monera do not possess a cellulose cell wall. Finally, prokaryotic organisms
reproduce through a process called binary fission.
In binary fission, one parent cell
replicates its genetic material and then reproduces into two identical daughter
cells. Since only one parent is involved,
this is a method of asexual reproduction. This allows us to eliminate the
answer choice that says that these organisms reproduce sexually. The answer choice that describes a
characteristic of an organism belonging to kingdom Monera is the cells of these
organisms do not contain a membrane-bound nucleus.
Let’s try another practice
question.
A unicellular organism has been
discovered. The organism is adapted to survive
in hot springs that have very high temperatures and low pH levels. Which kingdom, Archaebacteria or
Eubacteria, is this organism most likely to belong to?
This question describes some of the
characteristics of an unidentified unicellular organism. And then it asks us which of two
kingdoms, Archaebacteria or Eubacteria, is this organism most likely to belong
to. In order to answer this question,
we’ll recall the characteristics of organisms that are classified as archaebacteria
and organisms that are classified as eubacteria. And then we’ll use the information
about the mystery organism to determine which of the two groups it most likely
belongs to.
In order to best organize what we
know about these two kingdoms, I’ve made a Venn diagram. There’s one section for eubacteria,
one section for archaebacteria, and where the two circles overlap represents
information that’s true about both. Organisms that belong to kingdom
Eubacteria as well as organisms that belong to kingdom Archaebacteria can be
described as prokaryotic. Prokaryotic organisms are
unicellular, they’re asexual, and they have cells that do not possess a
membrane-bound nucleus.
The word eubacteria means true
bacteria. These are the bacteria that you’re
likely already familiar with. Eubacteria exist nearly everywhere
on Earth, and they possess a cell wall made of a chemical called peptidoglycan. The word archaebacteria means
ancient bacteria. These organisms got their name
because they were first discovered existing in extreme environments. These environments are similar to
ones that were much more common on Earth a long, long time ago. Another distinguishing
characteristic of archaebacteria is that their cell walls are not made of
peptidoglycan.
We’ve determined the
characteristics of archaebacteria and eubacteria. So, now we need to review the
characteristics of our mystery organism and figure out which kingdom it belongs
to. We’re first told that our organism
is unicellular, but that’s a characteristic of both archaebacteria and
eubacteria. So, being unicellular doesn’t help
us to figure out which of the two kingdoms our organism belongs to.
We are also told that this organism
exists where temperatures are very high and pH is very low. While extremely high temperature
and low pH would kill most eubacteria, archaebacteria are known for existing in
extreme environments. A hot spring is a good example of
an extreme environment. So, we can conclude that the
kingdom that this unicellular organism is most likely to belong to is
Archaebacteria.
Let’s wrap up our lesson by taking
a moment to review what we’ve learnt. In this video, we learnt about the
kingdom Monera. We learnt that all of the organisms
in the kingdom Monera are prokaryotic. Prokaryotic organisms are
unicellular, their cells do not possess a nucleus, and they reproduce asexually. We also learnt that, more recently,
the kingdom Monera has been divided into two kingdoms, Bacteria and Archaea. The members of the Bacteria kingdom
can be found living nearly everywhere on Earth, and they have cell walls made of a
chemical called peptidoglycan. In contrast, archaea tend to live
in extreme environments, and they have a cell wall that is not made of
peptidoglycan.
