The closest and most profound bond between people and the earth is through plants. We occasionally see evidence of how plants have helped people in all facets of life. Plants support us everywhere, from our fundamental needs for food, oxygen, shelter, and clothing to our more advanced energy needs for fossil fuel. Therefore, it becomes essential to conduct a thorough study of the Kingdom Plantae. Let's take a quick look at some of the distinguishing traits of plants below.
What distinguishes the Kingdom Plantae as unique?
The fact that these are non-motorized beings is the most important point.
Chlorophyll, a green pigment found in them, aids in the production of their food. Plants are therefore autotrophs.
They can reproduce sexually or asexually through vegetative propagation.
Eukaryotes with multiple cells are plants. They have a big central vacuole and a stiff outer cell wall.
They also have distinct organelles for anchoring, reproduction, support, and photosynthesis, among other functions.
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How should the Plant Kingdom Plantae be further divided?
The plant kingdom spans a sizable area. This has made it necessary to further subdivide plants. Here is a list of the criteria that were used to separate them for this exact reason.
Plant Body: The physical makeup is a significant point of differentiation. centres on whether or not body parts like roots, stems, and leaves are present.
Vascular System: A plant's system for transporting fluids is a crucial component. Plants are divided because their phloem and xylem systems are clearly defined.
Seed Formation: Plants also have different reproductive strategies. Strong determining factors include whether they have flowers and seeds, and whether the seeds are exposed or enclosed in a fruit.
What are the primary plant classifications?
The plants are divided into five subgroups based on the aforementioned characteristics and factors;
Thallophyta
Bryophyta
Pteridophyta
Gymnosperms
Angiosperms
Thallophyta:
Thallophyta is polyphyletic, meaning that it has multiple common ancestors in the evolutionary tree. They can be filamentous, colonial, branched, or unbranched and have an extremely simple and primitive body structure called a thallus. Their typical examples include bacteria, lichens, fungi, algae, and more.
Characteristics of Thallophyta
True roots and the vascular tissue required to carry water and minerals are absent in thallophytes. As a result, they are typically found in damp and wet areas.
Most of their members are autotrophic and able to produce their own food. However, some species, like fungi, rely on other food sources.
Immediately following photosynthesis, the glucose that is created is consumed. Any remaining component is converted and stored in the intricate compounds known as starch.
Its cells are enclosed by a cellulose cell wall.
Phloem and xylem, which are vascular tissues, are absent from them.
After fertilisation, no embryo forms because the sex organs are simple, single-celled structures.
Algae and fungi are further divided into Thallophyta.
Algae:
Algae are straightforward, autotrophic, thalloid, and primarily aquatic organisms that contain chlorophyll. They reproduce vegetatively through fragmentation and sexually through the formation of gametes, which can exhibit isogamy, anisogamy, or oogamy. Chlorophyceae, Phaeophyceae, and Rhodophyceae are the three groups of algae. Additionally, they have been observed to form symbiotic relationships with sloths that are native to the rainforests of South and Central America. The moisture-retaining fur provides an environment that is nourishing for the algae, and in exchange, the algae provides the sloth with nutrients and protection from predators.
Fungi:
Fungus is a thallophyta that is heterotrophic and achlorophyllous, or incapable of producing chlorophyll. Fungi frequently rely on symbiosis with other algae and cyanobacteria to help them produce their food. In exchange, the fungi offer them protection from the sun's UV rays. Lichen is a fantastic illustration of this, where the fungi and algae work as one cohesive organism.
Bryophyta:
Bryophytes are primarily distinguished by their absence of vascular tissues. They have been referred to as amphibians of the plant kingdom because they can develop in both terrestrial and aquatic environments. Since bryophytes are thought to have evolved from charophytes, they are regarded as the first true plants to have ever existed. They frequently use mosses, marchantia, liverworts, and hornworts as examples.
Characteristics of Bryophytes
Their leaves and stems are simple. They have rhizoids for surface anchoring despite not having true roots.
Rhizoids are unable to absorb nutrients, unlike true roots.
Mosses frequently exude spores from their leaves, which move through water and establish new mosses in new locations.
They require water in order to grow and spread. They can survive in the arid region by going into suspended animation and coming back to life when they come into contact with water.
With the alternation of generations, bryophytes are the same as other embryophytes. There is a predetermined number of unpaired chromosomes in haploid gametophyte cells. This results in the development of a diploid sporophyte with twice as many paired chromosomes. Gametophyte-produced haploid sperm and eggs are combined to create diploid zygotes. Sporophytes are formed from diploid zygotes.
Pteridophyta:
For hundreds of millions of years, fern-like plants were widespread before plants evolved flowers. These kinds of plants are quite similar to pteridophytes. Pteridophytes are strikingly different from other plants in that they reproduce through spores rather than seeds.
Divison of Pteridophytes
Pteridophyta are divided into four major groups:
Psilopsida:
They are the least developed.
Photosynthesis occurs in the dichotomously branched stems.
There are rizoids.
Almost no leaves are present.
It is a homosporous synangium, the sporophyte.
Tmesipteris and Psilotum are two examples.
Lycopsida:
They are frequently referred to as club moss.
They have a distinct plant body with rhizophores, leaves, adventitious roots, and stems.
There are homosporous or heterosporous sporophytes.
Lycopodium and Selaginella are two examples.
Sphenopsida:
Most people refer to them as horsetails.
They have a distinctive plant body made up of a stem, scaly leaves, and roots that grow from the nodes of an underground rhizome.
Sporangia that are homosporous are carried by strobili.
A good example is equisetum.
Pteropsida:
They are frequently referred to as ferns.
They have a distinct plant body, complete with roots, stem, and leaves.
There are homosporous or heterosporous sporophytes.
Multiflagellate antherozoids are present.
Pteris, Dryopteris, and Adiantum are a few examples.
Characteristics that Define Pteridophyta
Most people think that the oceans are where life first began. The first plants to have evolved and adapted to live in a lab are thought to be pteridophytes.
Pteridophytes are seedless plants. They spread spores to reproduce. They have vascular tissues, but xylem vessels and phloem companion cells are absent.
They have a very clearly defined root, stem, and leaf structure for their body.
The structure where spores are made is called a sporangium, and it is present in pteridophytes. They can produce one or two different types of spores and are both homosporous and heterosporous.
The leaves that bear the sporangia, or sporophylls, are what are used to create sporangia. The leaf's tips curl inward to cover the growing parts that are most vulnerable.
Pteridophytes exhibit alternation of generations and share the same life cycle as plants that produce seeds. Both the haploid gametophyte and diploid sporophyte generations are autonomous and free-living, unlike mosses and seed plants. Further categories for pteridophytic gametophytes' sexuality include:
Dioicous: means that each gametophyte either produces archegonia and egg cells for female reproduction or antheridia and sperm for male reproduction.
Monoecious: Each gametophyte can function as both a male and a female and can produce both antheridia and archegonia.
Antheridia: mature before archegonia in protandrous organisms.
Archegonia: mature before antheridia in a protogynous organism.
Gymnosperms:
Gymnosperms have a distinctive plant body with a vascular structure and the ability to produce seeds. Their name derives from the Greek words gymno, which mean spermatic as seeds that are not enclosed within a fruit and are therefore naked. Evergreen woody trees like pines, deodar, and redwood are some of their examples.
Characteristics of Gymnosperms
Gymnosperms have undergone extensive evolutionary change and exhibit some distinctive traits like a lack of flowers and open, bare seeds. Since they don't produce flowers, fruits are also missing in this situation.
Their primary means of seed dispersal and self-pollination is the wind. They range in height from medium to tall, with a few shrub classes also being offered. One of the largest and tallest tree species is the gymnosperm known as the sequoia.
They have clearly defined and recognisable body parts. The leaves have a structure similar to that of a needle, have thick cuticles, and have sunken stomata, which are typical of conifers and reduce water loss during transpiration.
Angiosperms:
The Greek words angio, which means confined, and sperma, which means seed, are used to describe angiosperms. They have seeds and a distinct plant body, just like gymnosperms, but in this case, the seeds are enclosed in fruits. These are flowering plants, and the cotyledons—seeds made from developing leaves—are what these plants produce. Mango and pomegranate plants are two examples.
Each angiosperm plant has a vascular bundle with xylem and phloem to carry nutrients, water, and minerals. an organised body with a root system, shoot, and leaves. The flowers where male and female gametes mature and where, after pollination, these flowers transform into fruits containing the seeds, are remarkably distinctive features.
Angiosperms have a wide variety in their habitats and sizes. They range in size from the tiniest Wolfie to the tallest 100-meter Australian mountain ash tree. Numerous plants grow into tall woody trees, shrubs, and herbaceous plants with additional root, stem, and leaf adaptations based on their habitat needs.
Division of Angiosperms:
Angiosperms are divided into monocotyledons and dicotyledons based on the types of cotyledons that they have. The monocotyledonous angiosperms only have one cotyledon, while the dicotyledonous angiosperms have two cotyledons in their seeds.
Monocotyledonous Plants:
The monocots have simple leaves with similar venation, adventitious roots, and trimerous flowers. Vascular bundles are more numerous and closed than before. Examples include cereals, lilies, bamboos, bananas, sugarcane plants, and banana plants.
Dicotyledonous Plants:
The two cotyledons, taproot arrangement, and reticulate venation in the leaves are characteristics of dicotyledonous plants. Tetramerous or pentamerous flowers exist. Between two and six vascular bundles are arranged in a ring. Sunflowers, tomatoes, dandelions, grapes, and potatoes are a few examples.
Secondary Plant Division: Phanerogams and Cryptogams
Plants are also divided into cryptogams and phanerogams based on their ability to produce seeds.
Cryptogams are plants that reproduce through spores rather than seeds because they lack a well-developed or visible reproductive system. This group includes the thallophytes, bryophytes, and pteridophytes.
Phanerogams are plants that have a visible, well-developed reproductive system and can produce seeds. Angiosperms and Gymnosperms both have a place in the phanerogams group.
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