Video Transcript
In this video, we learn how to
recall the characteristics of organisms belonging to kingdom Plantae. We are going to look at groups of
plants in more detail including higher algae and nonvascular and vascular
plants.
The planet Earth has an incredibly
diverse range of living organisms. To make these organisms easier to
study, scientists have classified them into distinct groups according to their
physical characteristics or evolutionary history. This process is called
taxonomy. All living organisms that have been
discovered so far can be classified into three domains: Bacteria, Archaea, and
Eukaryota. They can then be classified further
into kingdoms, which are groups containing a large number of organisms sharing some
characteristics. The further down the classification
we go, the more specific are the characteristics of the organisms.
Let’s have a look at the kingdoms
and specifically the organisms within the kingdom Plantae. In 1969, a scientist named Robert
Whittaker proposed the five-kingdom classification system. He divided all living things into
the kingdoms Monera, consisting of all prokaryotic organisms; Protista, consisting
of eukaryotic, unicellular organisms or simple cellular colonies; Fungi; Plantae;
and Animalia.
Kingdom Plantae is a large
taxonomic group that contains all the species that we commonly refer to as
plants. Scientists estimate that we have so
far identified nearly 400,000 different species of plants. And these plants inhabit almost
every environment on Earth. Without organisms like plants
producing the oxygen that we need to breathe, human life would cease to exist.
But what are the common
characteristics that make a plant a plant? Plants are all eukaryotic, which
means that their cells, which are enclosed by a cell membrane, contain a
membrane-bound nucleus and other membrane-bound organelles. The cells of organisms belonging to
the kingdom Plantae have other shared features unique to the cells of this
kingdom. Their cells are surrounded by a
cell wall, which provides structure and support. The main component of these cell
walls is the polymer cellulose. Plants are autotrophic. This means that they’re able to
make their own food from inorganic materials. They do this through
photosynthesis, which is carried out in organelles called chloroplasts.
Photosynthesis converts the
inorganic materials carbon dioxide and water in the presence of light energy into
glucose, which the plant can use as a food source. This process also releases oxygen
that the plant can use in cellular respiration or release into the atmosphere.
The kingdom Plantae can be divided
into rough groups: higher algae, nonvascular plants, and vascular plants. You might’ve noticed the dashed
line to the group higher algae. This is because some more recent
classification systems now place higher algae in kingdom Protista. But as they share some key
characteristics with kingdom Plantae, we’re going to look at them in this video. So that we’ve got some more space
to explore the different characteristics of these three groups, let’s remove the
rest of the information on the screen.
Higher algae are photosynthetic
organisms that inhabit aquatic environments. Phyla that are considered higher
algae include Rhodophyta, Phaeophyta, and Chlorophyta. Rhodophyta are more commonly known
as red algae because their cells contain red photosynthetic pigments and therefore
appear red. They mostly inhabit marine
environments, and their cell walls have gelatinous coats that stick to other
cells. An example organism of a red algae
is Polysiphonia.
Phaeophyta are more commonly known
as brown algae, and they have cells containing brown photosynthetic pigments and
therefore appear brown. They also inhabit marine
environments and can have simple or branched filaments. An example organism of the brown
algae is Fucus.
The final phylum Chlorophyta is
also known as green algae. As you probably guessed, their
cells contain chloroplasts, sometimes also called chloroplastids, which contain
green pigments. They may inhabit either freshwater
or marine aquatic environments and may either be unicellular or multicellular. One example of a green algae, which
when observed under a light microscope reveals spiral-shaped chloroplasts in its
cells, is called Spirogyra.
There are two more divisions that
are sometimes considered phyla in kingdom Plantae: Bryophyta and Tracheophyta. The organisms belonging to the
Bryophyta division are nonvascular plants, whereas organisms belonging to
Tracheophyta are vascular plants. But what does vascular and
nonvascular mean? Nonvascular plants do not have
complex or specialized vascular tissues as vascular plants do. Specialized vascular tissues are
cells joined together into a network of tubes. These are used to transport water
and mineral ions from the roots to the rest of the plant and other nutrients like
sugars and amino acids mainly from the leaves, where most of them are produced, both
up and down the plant to all the cells that might require them.
There are two different types of
vascular tissues with different cell structures that transport these different
substances. They are called the xylem and the
phloem. We’ll back to these vascular
tissues in just a little while, but first let’s review the key characteristics of
nonvascular plants.
The most important feature is of
course that they do not have a vascular system. We also mentioned that they contain
the phylum or division Bryophyta, which in turn consists of three further divisions:
mosses, liverworts, and hornworts. The word bryophyte comes from the
Greek bryon, meaning tree moss or oyster green, and phyton, meaning plant. Bryophytes are characteristically
limited in size, and they tend to prefer moist habitats, although they have been
shown to survive in drier environments. They produce enclosed reproductive
structures called gametangia and sporangia, but they do not produce flowers or
seeds.
Bryophytes may also have structures
called rhizoids, which extend from their lower epidermis cells to help anchor the
plant into the ground. An example of a nonvascular plant
is Funaria hygrometrica, which is a type of moss. These mosses live in very moist
environments to ensure that they have constant access to water and minerals.
Let’s take a look at the
characteristics of vascular plants next, which is probably the group of plants with
which you’ll be most familiar. Organisms belonging to the division
or phylum Tracheophyta have specialized vascular tissues. As we mentioned earlier, these
tissues include the xylem and the phloem. The phloem is responsible for
transporting sugars that are produced in the photosynthetic part of a plant such as
the leaves and amino acids to the parts of the plant that require them. A useful feature of the phloem is
that it can transport these substances both up and down the plant. The xylem on the other hand
transports water and mineral ions that are absorbed into the roots upwards through
the stem to the leaves, flowers, and fruits of a plant. This transport happens in only one
direction, upwards.
Tracheophyta can be further divided
into three groups: Filicatae, Gymnospermae, and Angiospermae. Plants belonging to the group
Filicatae are more commonly known as ferns. The majority of ferns are found as
herbs, and some are shrubs or trees. They have stems, leaves, and roots
extending through the ground. Ferns do not produce flowers or
seeds but instead reproduce using small reproductive structures called spores. Their leaves have a pinnate
shape.
Plants belonging to the subdivision
Gymnospermae are largely trees. These plants produce seeds that are
not enclosed in other structures, which is in contrast to many other classes of
plants. In fact, the word gymnosperm comes
from the Greek words for naked and for seeds. So the name literally translates to
naked seeds. Similar to ferns, gymnosperms do
not produce flowers, but they do carry cones, which can be male or female. They have simple leaves that form
needle shapes. Some examples of gymnosperms are
the firs and pines that some people often use as Christmas trees.
Angiospermae is a subdivision of
Tracheophyta that includes flowering plants. These plants inhabit the land, and
they produce flowers, leaves, seeds, and fruits. This class can be further divided
into two groups: monocotyledons and dicotyledons, sometimes known as monocots or
dicots. Let’s take a closer look at the
distinction between monocots and dicots.
A cotyledon is referred to as the
embryonic leaf of a plant, which is contained within the plant seed. It is an important part of the
embryo within a plant seed. The prefix mono- means one, and the
prefix di- means two. Scientists can use the cotyledon to
classify angiosperms into monocotyledons, which have one cotyledon, and
dicotyledons, which are seeds that have two cotyledons. We know that monocots and dicots
differ in their seed structure. They also have various other
important structural and functional differences. For example, in the roots of
monocots, the vascular bundles are arranged differently. The xylem and the phloem are
arranged in a ring, while in dicots the phloem is found between the arms of the
xylem vessels.
Furthermore, the roots of a monocot
are usually branching and fibrous, but a dicot is likely to have one main or taproot
from which smaller roots can branch. In the stems of monocots the
vascular bundles are scattered, while in dicots they are arranged into distinct
rings. Another difference is the pattern
in which the veins form in the leaves. The leaves of monocots are narrow
with parallel veins, while dicots have pinnate- or palmate-shaped leaves. And their leaf veins form a net
pattern. Finally, they differ in the amount
of flower structures. Monocots have flower parts in
threes or multiples of threes, while dicots have flower parts in fours, fives, or
their multiples. An example of a monocot is corn,
and an example for a dicot is a sunflower.
So let’s summarize. Scientists order organisms into
five kingdoms. One of the kingdoms of life is
kingdom Plantae. Kingdom Plantae can be divided into
three groups with different characteristics: higher algae, nonvascular plants, and
vascular plants. Nowadays, the group higher algae is
not included in kingdom Plantae but instead in kingdom Protista. Let’s apply what we’ve learned
about kingdom Plantae to a practice question.
The picture provided shows an
organism belonging to the kingdom Plantae. What are the characteristics of
organisms belonging to this kingdom? (A) These organisms are eukaryotic,
multicellular, and heterotrophic. (B) These organisms are
prokaryotic, multicellular, and autotrophic. (C) These organisms are eukaryotic,
multicellular, and autotrophic. Or (D) these organisms are
prokaryotic, multicellular, and heterotrophic.
To answer this question, let’s
start by reviewing what the terms eukaryotic, heterotrophic, prokaryotic,
multicellular, and autotrophic mean. Organisms that are eukaryotic and
organisms that are prokaryotic differ considerably in their cellular structure. Eukaryotic cells contain
membrane-bound organelles including a membrane-bound nucleus, which prokaryotic
cells do not. While the DNA in eukaryotic cells
is packaged into multiple chromosomes found in this nucleus, in prokaryotic cells
it’s found in the form of circular chromosomes and several plasmids found loose in
the cytoplasm.
Most prokaryotic cells are
unicellular, meaning they’re made up of only one cell like a bacterium. Most eukaryotes however are
multicellular. This means that they’re made up of
multiple often differently specialized cells like we humans are. As plant cells like this one do
have a nucleus and other membrane-bound organelles like chloroplasts, we know that
they’re eukaryotic and multicellular. So we can exclude options (B) and
(D), as both of these say that they are prokaryotic.
Now we just need to work out
whether plants are heterotrophic or autotrophic. So let’s look at these terms
next. These two terms refer to how
organisms can obtain their food. Some autotrophs, like this plant,
can obtain their food by synthesizing it themselves through photosynthesis. They use water absorbed from the
soil and carbon dioxide absorbed from the atmosphere in the presence of light energy
usually from the sun to produce simple sugar molecules like glucose, which they can
then use to make more complex nutritious molecules. As autotrophic organisms only need
light in addition to these simple inorganic materials in order to produce their
food, they are often sessile, meaning they do not move around.
Heterotrophic organisms on the
other hand need to obtain their food from another living or once-living
organism. Heterotrophs must consume other
organisms in order to obtain their nutrition. They therefore need to be able to
move around the place to find or hunt other organisms to eat.
We know that plants can produce
their own food via photosynthesis, so they’re autotrophic. As we know that plants are not
heterotrophic, we can exclude option (A). So we’ve worked out that the key
characteristics of organisms belonging to kingdom Plantae are that these organisms
are eukaryotic, multicellular, and autotrophic.
Let’s review the key points that
we’ve covered in this video. Organisms that belong to kingdom
Plantae are autotrophic, multicellular, and eukaryotic. Higher algae are sometimes
classified under kingdom Plantae, and they include the divisions Rhodophyta,
Phaeophyta, and Chlorophyta. Bryophyte are another group
belonging to kingdom Plantae, and they are nonvascular plants that include mosses,
liverworts, and hornworts. The group Tracheophyta also belongs
to kingdom Plantae, and these include vascular plants such as Filicatae,
Angiospermae, and Gymnospermae. The Angiospermae division includes
flowering plants, and these can be subdivided into monocotyledons and
dicotyledons.