Lesson Video: Kingdom Plantae Biology

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.