Question

QUESTION 3 a. Explain the major groups of plants. b. Explain the classification of the plants. TT T Arial 3 (12pt) T- 5 - Path:p

Answer 1

The kingdom Plantae contains four major groups of land plants: bryophytes, pteridophytes, gymnosperms, and angiosperms.

Plant life is diverse, adaptive, and environmentally successful. This means they exist in many of Earth's ecosystems. All plants are autotrophs, producing their own food through photosynthesis, which makes food using light, and thus plants provide food to an array of consumers and decomposers. The kingdom Plantae consists of four major plant groups on land: bryophytes (mosses), pteridophytes (ferns), gymnosperms (cone-bearing plants), and angiosperms (flowering plants). Plants may be categorized as vascular or nonvascular. A vascular plant has tissues for transporting water or sap. Nonvascular plants do not. Plants may also be classified as seed-bearing or spore-producing. Gymnosperms and angiosperms produce seeds, while bryophytes and pteridophytes produce spores.

Plants have varied, unique structures, yet all plants are eukaryotic organisms, meaning they have a cell nucleus and membrane-bound organelles. Plants exist in all types of ecosystems. Angiosperms have more than 260,000 living species. Gymnosperms include the oldest (bristlecone pine), the tallest (redwoods), and the thickest (Montezuma bald cypress) living species. At the opposite end of the plant spectrum are green algae, some of which are single-celled. Phytoplankton produce more than half the world's oxygen, far more than the Amazon rainforest or the large areas of grasses on the plains. Although these phytoplankton technically fall under the kingdom Plantae, they are not part of the four major groups already discussed, which include only land plants.

Although the life cycles of plant groups may seem different, they all have some characteristics in common. All plants undergo a process called alternation of generations, a cycle that consists of a sporophyte generation – diploid (which has a double set of genetic material) and a gametophyte generation – haploid (which has only a single set of genetic material).

The major plant groups include bryophytes (mosses), pteridophytes (ferns), gymnosperms (conifers), and angiosperms (flowering, seed-bearing plants). Mosses are short plants and their leaves are usually only one cell thick. Ferns have many leaves branching out from their fronds. Conifers typically have needle-like leaves. Flowering plants produce flowers, which are often brightly colored to attract pollinators.

FIGURE 21-2 Evolutionary tree of some major plant groups Bryophytes Tracheophytes seed plants Liverworts Mosses Ferns Gymnosperms Angiosperms Flowers and fruits appear. Seeds and pollen appear. True vascular tissue and lignin appear. Ancestral green alga

Classification of Plant Kingdom

Based on whether plants have a well-differentiated body and the presence or absence of specialized tissues for transport, and the ability to bear seeds Kingdom Plantae (Plant Kingdom) is can be classified into different divisions. The features and examples of each division are mentioned hereunder.

Division Thallophyta

These are the lowermost plants of the plant kingdom, without a well-differentiated body design. This means that the plant body is not differentiated as roots, stem, and leaves. They are commonly called algae, are permanently aquatic. Examples include Spirogyra, Chara, and Ulothrix.

Division Bryophyta

These are small terrestrial plants. They show differentiation in the body design, with stem, leaf-like structures, and root-like structures. But, they do not have any specialized tissue to conduct water and other substances. They live in damp and sandy habitats and are often referred to as the amphibians of the plant kingdom. Examples are Riccia, Funaria, and Marchantia

Division Pteridophyta

These are supposed to be the oldest vascular plants. The plant body is differentiated into roots, stem, and leaves, apart from having a specialized tissue for conduction. This tissue helps in the conduction of water and other substances from part of the plant to the other.

These plants have naked embryos called spores. The reproductive organs in these plants are inconspicuous. Examples: Marselia, Ferns

Division Phanerogamae

Phanerogams are seed-bearing plants. The plant body is well differentiated with stem, leaves, and roots. There are well differentiated reproductive tissues that produce seeds. These plants also have a well-developed vascular system.

Depending on whether the seeds produced are naked or whether they are enclosed, phanerogams are further classified into two subdivisions. They are Gymnosperms and Angiosperms

Gymnosperms

Gymnosperms are plants with naked seeds. There are about 650 living species of gymnosperm plants. The plants are usually perineal, evergreen and woody.

They have a well-developed vascular tissue but do not have vessels. The reproductive organs generally form cones or strobilus. There is no fruit formation and the seeds are hence said to be naked. Examples: Cycas, Pinus, Deodar

Angiosperms

Angiosperms are seed-bearing plants. Seeds develop inside tissues that get modified to form the fruit of the plant. Also called the flowering plants, they are found abundantly in nature. These plants are usually terrestrial and they may be annual, biennial or perennial. The vascular system is very well developed with xylem and phloem. Angiosperms also show the feature of double fertilization. Examples: Mustard plant, Pea plant.

On the basis of the cotyledons (seed leaves) Angiosperms are further divided into Monocotyledonous plants and Dicotyledonous plants. Monocots have seeds with single seed leaf, having vascular bundles arranged in a complex manner. Dicots, on the other hand, have two cotyledons. The vascular bundle is arranged in a ring.

Plants Do not have differentiated plant body Have differentiated plant body Thallophyta (Division 1) without specialised vascular tissue with vascular tissue Bryophyta (Division 2) Do not produce seeds Produce seeds Pteridophyta (Division 3) Phanerogamae Bear naked seeds Bear seeds inside fruits Gymnosperms (Division 4) Angiosperms (Division 5) Have seeds with two cotyledons Have seeds with one cotyledon Dicots (Subdivision 1) Monocots (Subdivision 2)