Plantae, Definition, Characteristics, Classification and Importance

Plantae: Kingdom Plantae, also called the plant kingdom, is one of the most fundamental groups in biology. It includes a vast diversity of organisms, ranging from tiny mosses to towering trees. Plants play a crucial role in the earth's ecosystems by producing oxygen and serving as the primary source of food for many organisms, including humans.

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Definition of Plantae

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Characteristics of Plantae

• Cell Structure: Plants are eukaryotic and have cell walls made of cellulose. Their cells also contain chloroplasts, the organelles responsible for photosynthesis. Other organelles, such as a large central vacuole, are also common in plant cells.
• Photosynthesis: One of the most crucial characteristics of plants is their ability to carry out photosynthesis . Using sunlight, carbon dioxide, and water, plants produce glucose and release oxygen as a byproduct.
• Autotrophic Nutrition : Plants are autotrophs, meaning they can produce their own food. This distinguishes them from heterotrophic organisms, which must consume other organisms for energy.
• Reproduction : Plants can reproduce sexually, involving gametes, or asexually, through methods like budding, fragmentation, and vegetative propagation. In higher plants, reproduction often involves complex life cycles that alternate between a diploid (sporophyte) stage and a haploid (gametophyte) stage.
• Growth and Development : Plants exhibit indefinite growth due to the presence of meristematic tissues, which allow continuous growth at specific regions like roots and shoots.
• Life Cycle: Most plants show alternation of generations, where they alternate between a multicellular diploid (sporophyte) phase and a multicellular haploid (gametophyte) phase. This complex life cycle allows for genetic variation and adaptability in plants.

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Classification of Kingdom Plantae

Thallophyta (Algae)

• Cryophytes : These algae thrive in cold environments, growing on snow or ice.
• Thermophytes: Found in hot water habitats, these algae can survive high temperatures.
• Epiphytes: Epiphytic algae grow on other plants, including other algae or angiosperms. Examples include Oedogonium, Cladophora, and Vaucheria.
• Endophytes : Certain blue-green algae grow inside other plants. For instance, Anabaena can be found as an endophyte inside the leaves of the fern Azolla.
• Parasites : Cephaleuros virescens is an example of a parasitic alga that grows on tea leaves.
• Algae play a crucial role in ecosystems as primary producers, providing oxygen and food to aquatic organisms. They are also economically important, with certain algae used in food, medicine, and industrial applications.

Bryophyta

• Structure and Reproduction: Bryophytes have a simple body structure with no true roots, stems, or leaves. They reproduce sexually with distinct male and female reproductive organs:
  • Antheridium is the male sex organ that produces motile sperm.
  • Archegonium is the female sex organ that produces eggs.
• Habitats and Adaptations : Bryophytes are predominantly found in moist environments, but certain species have adapted to a variety of conditions, from arid regions to watery habitats. Bryophytes are ecologically significant as they play a role in soil formation and prevent soil erosion.

Pteridophyta

• Structure and Reproduction: Pteridophytes possess true roots, stems, and leaves. They reproduce through spores and follow an alternation of generations, with a dominant sporophyte phase. The sporophytic plant body has a single apical cell with three cutting faces in the shoot apex.

Classification of Pteridophytes:

• Pteridophytes are classified into four main sub-phyla:
• Psilopsida: These are the oldest known vascular plants, mostly found as fossils, with a relatively undifferentiated body. Examples include Psilotum, and they lack true roots, instead having a dichotomously branched rhizome
• Lycopsida (Club Mosses) : Plants in this group have a well-differentiated body with roots, stems, and leaves. Leaves are typically small (microphyllous) with a single, unbranched vein, and sporangia develop in the axils of sporophylls.
• Sphenopsida (Horsetails): Characterized by jointed stems with nodes and internodes, these plants have microphyllous leaves arranged in whorls at each node. An example is Equisetum.
• Pteropsida (True Ferns): These plants have a highly differentiated body with roots, stems, and large, pinnately compound leaves (megaphyllous). Examples include species like Pteris and Adiantum.

Gymnosperms

Gymnosperms , meaning "naked seeds," are plants whose ovules are not enclosed by an ovary wall and remain exposed before and after fertilization. They include medium-sized trees, tall trees, and shrubs, with the giant redwood (Sequoia) being one of the tallest tree species. Notable features of gymnosperms include:

• Roots: Typically tap roots, with some associated with fungi (mycorrhiza) or nitrogen-fixing cyanobacteria (e.g., Cycas).
• Stems : May be unbranched or branched, with simple or compound leaves.
• Reproductive structures: Gymnosperms are heterosporous, producing haploid microspores and megaspores within sporangia on sporophylls. The male strobili (cones) produce pollen grains, while female strobili bear ovules.

Angiosperms

• Dicotyledons typically have taproots.
• Leaves show reticulate (net-like) venation.
• Flowers are tetramerous or pentamerous, having four or five floral parts.
• These are arranged in a ring, typically with 2–6 open bundles that contain cambium.
• Dicots have two cotyledons (seed leaves).

• Monocots generally have adventitious roots.
• Leaves have parallel venation.
• Flowers are trimerous, with three parts per floral whorl.
• Scattered in the ground tissue and closed (without cambium).
• Monocots have a single cotyledon. Examples include cereals, bamboos, sugarcane, palms, bananas, lilies, and orchids.

Importance of Kingdom Plantae

MCQs of Plantae

Q1. Kingdom Plantae includes;

1. All eukaryotic chlorophyllous organisms.
2. Some prokaryotic chlorophyllous organisms.
3. Few eukaryotic partial heterotrophic plants.
4. Few prokaryotic partial heterotrophic plants.

1. A and C
2. B and D
3. A, B, and C
4. A, C and D

Q2. How many of the following are not included in the plant kingdom? Algae, fungi, bryophyte, bladderwort, pteridophyte, gymnosperm, angiosperm

1. Zero
2. One
3. Two
4. Three

Answers of MCQs of Plantae