Kingdom Plantae
Kingdom Plantae
Definition of Kingdom Plantae
Plants are multicellular, autotrophic organisms that have successfully invaded terrestrial environments. They probably arose from the algal division Chlorophyta. When plants established themselves on land, they significantly improved the prospects for active photosynthesis.
Adaptation of Kingdom Plantae in Land, Desert and Rain Forests
Light is more available on land. Where it is filtered only through the atmosphere, then it is in the often churning and murky waters of lakes and seas. Another fundamental element for photosynthesis, CO2 is also much richer and readily absorbable on land than in the water. Virgin raids of land were probably highly successful for these reasons. Especially at a time when few enemies of the green plants had gained a foothold in terrestrial habitats.
Transition stages of Kingdom Plantae
Transition stages from water to land probably occurred at or near the shoreline. There evaporation concentrated minerals, leaving rich deposits. On the shores of rivers, alluvial (riverborne) deposits also provided a rich matrix for the development of new plant forms.
From Water to Land to Desert
Life on land required new styles of reproductive activity. Films of water allowed some plants to cling to the old aquatic reproductive strategies. But as plants migrated to drier regions, these strategies had to be modified.
Kingdom Plantae’s Plant Adaptations
Maintenance of the plant on land also required protection against desiccation. The outer cell layer (epidermis) of all plant bodies is covered completely by a layer of waxy material called cutin. Although individual epidermal cells secrete cutin, the cuticle does not become subdivided but exists as a continuous waxy layer. The water-resistant cuticle is generally thicker in exposed areas, such as the upper surface of a leaf, than in less exposed areas, such as the lower surface of the leaf.
Evolution of Plants Timeline
More than 400 million years ago the ancestral forms of today’s land plants began to spread through the terrestrial environment. As they moved into major land areas, they evolved adaptations that facilitated their survival.
A major division into two separate lineages occurred early in the colonization of the land.
- One group was the bryophytes.
- the other, far more numerous in the modern era (Cenozoic), the tracheophytes(vascular plants).
Non-vascular Plants (Bryophytes) of Kingdom Plantae
Non vascular plants (Bryophytes) consist of three extant groups.
1. Mosses of Kingdom Plantae
About two-thirds of all species of bryophytes are mosses. Although the bryophytes have developed some protective structures (Figure 1), they are not eminently suited to a terrestrial existence.
Characteristics of Mosses
They require moist environments, particularly for their reproductive cycles. Although they do have processes that resemble the roots of higher plants, and even demonstrate chlorophyll-laden scales, they are clearly only a stage in the evolution of the higher land plants. The bryophytes are much more common in warm climates than in cold, or even temperate, regions.
The mosses are both more numerous and more visible than other bryophytes (bryo means “moss”). Lacking the internal support structures of the higher plants, mosses tend to spread extensively but grow very close to the ground. Like other bryophytes, they show a dominant gametophyte (haploid) generation and a dependent sporophyte (diploid) generation (Figure 1). Most mosses are dioecious (have separate sexes) but some are monoecious (have both sexes in the same thallus or plant body).
Bryophytes Life Cycle
2. Liverworts
The liverworts are named for their flat, lobular appearance, resembling the lobes of the liver, wort means “herb” or “plant.”
Example of Liverwort
Marchantia is a liverwort that shows clearly the partial adaptation to terrestrial life of the bryophytes. Rhizoids, single hairlike cells, extend from the ribbon-shaped thallus of Marchantia into the ground, where they absorb water. Motile sperm swim through a layer of water to reach the egg, making moisture a necessary ingredient in the fertilization process. Special protective receptacles produce both sperm and eggs, which is a major advance over algae. Antheridia form the sperm, while archegonia produce the eggs.
Figure 2. Marchantia Life Cycle
3. Hornworts
The hornworts are a minor group of bryophytes, possessing some features of higher plants. They get their name from the hornlike sporophyte that grows up from the flattened gametophyte.
Vascular Plants of Kingdom Plantae
Definition of Vascular Plants of Kingdom Plantae
Vascular plants differ from the bryophytes in their greater adaptiveness to land environments. Unlike the thallus of a moss or a liverwort, the body of a vascular plant is divided into separate parts, or organs. Which show specialization of both structure and function, roots, stems, and leaves (Figure 3). In the seed-bearing plants, cones or flowers comprise special reproductive structures.
Structure of Vascular Plant
Function of Roots in Kingdom Plantae
- The roots are an extensive system of ramified fibers that anchor the plant firmly in the ground.
- The slender hairs that extend from the ends of younger roots absorb water and minerals and bring these vital materials to the rest of the plant.
- This specialized root system supplies the above-ground structures of the plant with water to carry out photosynthesis.
Stem Function in Kingdom Plantae
- The stem affords an opportunity for the plant to grow upward, sometimes, as in the case of trees, to great heights.
- The vascular tissue within the stems conducts vital raw materials from roots to peripheral areas.
- Brings synthesized food down from the leaves.
- It also provides the support that enables vascular plants to stand tall.
Function of Leaves
The leaves of tracheophytes are ideally suited for receiving maximum exposure to the sunshine necessary to their role as primary photosynthetic agents for the entire plant.
Evolution in Vascular Plants
Possible transition forms in the evolution of vascular plants from multicellular algae belong to the division Psilophyta. These plants were once abundant on the earth but now occur in only a few genera. They possess only some of the features of the vascular plants, but a primitive vascular system can be discerned. Some botanists regard the Psilophyta as forms that gave rise to other vascular types, but others consider them to be degenerate descendants of the more advanced types, such as ferns.
Example
Psilotum, an extant tropical genus, is a relatively simple form, which may have descended from the fossil psilophytes which died out about 3S0 million years ago. It has no true roots; its lower portion is a rhizome, a horizontal stem that lies along the ground and extends tiny rhizoids into the soil. What might be viewed as pseudo leaves are pairs of scales along the shoot. However, the presence of vascular bundles marks the genus as a vascular plant.
Seedless Vascular Plants of kingdom plantae
Club Mosses
The club mosses, or lycopods, belong to the division Lycophyta. They share a peculiar characteristic with the Psilophyta. The gametophyte generation is nonphotosynthetic and must rely on symbiotic fungi for nourishment. Lycophyta was the dominant land plant group in the swamps that covered the earth about 300 million years ago. Some groups of ancient lycopods formed tall trees; nothing but their fossils remain. Present-day lycopods, which consist of more than 900 species, are small. The tropical representatives are often epiphytes—plants that grow on other plants as a means of structural support. The lycopods have both true roots and true leaves. The sporophyte generation is dominant, the usual situation for tracheophytes. Spores that develop into the gametophyte are formed on special leaves called sporophylls.
Horsetails of kingdom plantae
Another division of seedless plants is Sphenophyta (horsetails). They too flourished in an ancient time but are represented today by only a single genus—Equisetum. They are mostly small, herbaceous (nonwoody) plants rarely exceeding 70 cm in height. The stems are usually hollow and jointed. Leaves typically form in whorls at each joint. Sporangia are carried in groups at the ends of a central stem. Such groups of sporangia form a strobilus, or cone, which is quite different from the sporophylls of the club mosses. It is this cone, resembling a horse’s tail, that gives the division its name. The small gametophytes of the horsetails are photosynthetic and live independently of the sporophyte. Each gametophyte is monoecious, containing both archegonia and antheridia.
Ferns
The ferns (Pterophyta) are the most extensive and numerous of the seedless plants, comprising more than 12,000 separate species. The leaves are both broader and more vascularized than in the lycophytes or sphenophytes. The seedless plants left a legacy in the extensive coal beds that were formed largely more than 300 million years ago. Since coal is the result of the compression of vegetable matter beneath the earth, the great forests that grew at that time have provided the fossil fuel for our modern industrial furnaces. The time span during which coal was formed from those great tracts of seedless plant forests is labeled by geologists the Carboniferous Period.
Seed Plants in kingdom plantae
The development of a seed represented the height of adaptiveness to a terrestrial environment in the plant kingdom.In all seed plants, not only does the sporophyte dominate, but also the plant reduces the gametophyte to a dependent structure that it retains within the archegonium of the sporophyte. Furthermore, the lower plants’ flagellated sperm gets supplanted by the process of pollination. In pollination, the plant achieves independence from water as a vehicle for fertilization. The tough coat of the seed houses the zygote and developing embryo, which will become a new sporophyte, and provides other sources of protection for them, liberating them from dependence on water.
Seed
The seed contains a partially developed sporophyte that has been arrested in its development. It is surrounded by stored food material and protected from a variety of environmental stresses by a tough integument (skin). The seed and its embryonic sporophyte can remain dormant for quite some time and then germinate (resume growth) when conditions are appropriate. Such properties in a reproductive structure considerably enhance the possibility for survival in the sometimes-harsh terrestrial habitat.
Evolution of Seed
The seed perhaps arose independently at different times in the evolution of plants. Some fossil “ferns” have even been found with structures that resemble the seeds of the spermatophytes (seed-bearing plants). Present-day seed plants are classified as gymnosperms and angiosperms.
Gymnosperms of kingdom plantae
Definition of Gymnosperm
The gymnosperms (from the Greek fot “naked seeds”) consist of four divisions. The earliest gymnosperms probably arose a little less than 400 million years ago. The four divisions of gymnosperms are quite distinct from one another. Some botanists regard their inclusion in a single group as artificial. The extinct seed ferns (pteridosperms) have also been considered a fifth division of this catchall taxon.
Classification of Gymnosperms
Many taxonomists consider each of these divisions to constitute a class.
Cycadophyta in kingdom plantae
The Cycadophyta were particularly abundant during the age of the dinosaurs (Mesozoic Era). They may have arisen from the ancient seed ferns. The cycads that are present today bear a striking resemblance to the palms; their common name is sago palm. They generally grow in warm climates.
Ginkgophyta
The Ginkgophyta survive today as a single species, the ginkgo, or maidenhair tree. It is very common as an urban ornamental tree because it is exceptionally resistant to air pollution (a great asset in large cities where both air and water may be quite polluted). Ginkgos are dioecious. Unfortunately, the female ginkgo emits an overpowering foul odor in the spring, which is related to its reproductive cycle. This characteristic strongly militates against its selection for a small household garden patch.
Gnetophyta in kingdom plantae
The Gnetophyta include three diverse groups of tropical or desert plants. Gnetum exists as a thick, upright vine; Ephedra and Welwitschia are desert shrubs.
Coniferophyta
The Coniferophyta (conifers) are the most conspicuous of the gymnosperms, especially in colder northern climates. Although particularly prominent during the Mesozoic Era, conifers continue to dominate many forests.
Redwoods of kingdom plantae
On the west coast of the United States are a group of trees known as redwoods. They may reach a height of 100 m, and their trunks may be 4 m in diameter. Some redwoods are reputed to be 1500 years old. The redwoods are gymnosperms belonging to the genus Sequoia. The giant sequoias are another species of this genus. Pines, spruces, firs, and hemlocks are among the familiar species. In almost all cases the leaves are considerably reduced in breadth to form needles or flattened scales.
Conifers of kingdom plantae
The most prominent feature of the conifers is the reproductive structure known as the cone. Female cones tend to be larger than male cones.
Pines
The pine, which is a typical conifer, usually has both male and female cones on the same tree. The life cycle of the pine is similar in many respects to the life cycles of the angiosperms.
Pinecone Seeds
Each scale of a pinecone is a sporophyll that gives rise to a sporangium (also called a nucellus in the female).
Male Pine Cone
The sporangium of the male cone meiotically produces many haploid microspores, each of which becomes a hard-coated, winged pollen grain. Inside these pollen grains, the haploid nucleus divides mitotically, producing four cells. These four haploid cells constitute the entire male gametophyte, known as the microgametophyte, and even two of these cells will degenerate. We refer to the two remaining cells as the degenerative cell nucleus and the tube cell (nucleus). We will discuss their functions in a moment.
Female Pine Cone of kingdom plantae
Each sporangium of the female cone is surrounded by an integument with a micropyle (a small opening) at one end (Figure 4). Inside the sporangium, four haploid megaspores are produced, three of which degenerate.
Through repeated mitotic divisions inside the sporangium, the fourth megaspore creates the female gametophyte, a haploid, multicellular mass called a megagametophyte. This female gametophyte then produces several archegonia at its micropylar end. Each of these develops an egg cell. The combined integument, sporangium, and mega- gemetophyte are called an ovule.
Female Pine Cone
Double Fertilization in Gymnosperm
When a pollen grain enters the female micropyle and contacts the sporangium, it develops a pollen tube, which penetrates the sporangium. The two pollen nuclei enter the tube, and the generative nucleus divides. The tube cell is associated with growth of the pollen tube and does not divide. One of the resulting daughter nuclei divides again, producing two sperm cells. When the pollen tube enters an archegonium, one of these sperm cells fertilizes the waiting egg. The zygote develops into an embryo inside the megagametophyte, which is still in the sporangium. Eventually, the ovule is released as a seed. Ovule is composed of a seed coat derived from the integument, stored food from the megagametophyte, and the embryo.
Angiosperms
Definition of Angiosperm
The flowering plants (angiosperms), whose seeds are contained within a “vase” (the ovary), are the most successful and widespread of all plants.
They arose more than 100 million years ago in the Cretaceous Period of the Mesozoic Era and became the dominant land plants of the Cenozoic, or modern, Era.
Angiosperms Life Cycle
Whereas the reproductive structures of the gymnosperms are cones which bear their ovules, or future seeds, on exposed scales of the cone, the reproductive structures of the angiosperms are flowers which completely enclose the future seeds. The longitudinal subsections of the pistil (the innermost structure of the flower containing the female reproductive structures) are called carpels. The carpels may have arisen as an in folding of sporophylls to make up the ovary, the style, and the stigma.
Angiosperm Life Cycle
Importance of Angiosperms
Close to 175,000 species of flowering plants exist. Insects pollinate flowers that tend to have large, magnificently colored petals and often emit a pleasant scent. These flowers have experienced extraordinary success in every possible terrestrial habitat as well as in lakes and ponds, but they appear quite meagerly in the seas. Although almost all angiosperms are autotrophs, a few lack chlorophylls and survive as saprophytes. Some have become parasites.
Types of Angiosperms
Angiosperms that endure through only a single growing season are known as annuals. Those that grow through two growing seasons, such as the carrot, are dubbed biennials. Perennials last for long periods of time.
Importance of Kingdom Plantae
Plants are a seemingly endless source of benefit to humans. The 250,000 species of angiosperms, in their roots, stems, leaves, and even flowers, provide food for almost all the animal world.
Dicots
Among the dicots are the Rosaceae: roses, strawberries, cherries, and almonds. They include some of the most common fruits and ornamentals. Alfalfa, beans, clovers, peas, etc., make up the Leguminosae family. The bacterial nitrogen fixation that occurs in the roots of many of these plants marks them as vital to agriculture. This family also includes many of the vegetables and stock feeds that are a mainstay of the agriculture of developed nations. Citrus fruits are part of the Rutaceae. Cruciferae include mustard, cabbage, cauliflower, and broccoli. Gourds, pumpkins, squashes, cucumbers, and the citron belong to the Cucurbitaceae.
Monocots
The most important monocots are the grasses, Graminae, a family with over 5000 species. This family includes bamboo, wheat, rice, maize, barley, and timothy. It is the single most important group of food plants. Other monocots include pineapples (Bromeliaceae) and date palms (Palmales).
Use of Kingdom Plantae
Many of the flowering food plants are herbs, which are relatively small, soft-stemmed plants. Most of the herbs are annuals, but they are also found as biennials and perennials.
Medicinal Plants
Many medicines are derived from plants. For example, quinine comes from the bark of the cinchona, digitalis comes from the foxglove.
Plant Fibers
Although manufacturers have made great inroads with synthetics in fabric production, designers still commonly use natural fibers such as flax (from the family Linaceae) and cotton for clothing, drapes, upholstery, and more.
Decorative Plants
The decorative uses of plants range from vast landscaping designs, involving great tracts of trees, flowers, and shrubs, to a simple flower arrangement in a vase. Wood is used in furniture making and construction. Use of wood as an alternative source of energy has seen a resurgence in recent decades in the United States in response to unstable oil prices. It is the only source of energy in many countries. A situation that has led to widespread deforestation, which in turn has precipitated devastating erosion and flooding. Coal itself is a plant product—albeit from ancient trees and more primitive tracheophytes.
Chemical Plant of Kingdom Plantae
The plant world provides thousands of industrial chemicals, including plastics, turpentine, tannin, and rubber, to name just a few. Although manufacturers now generally produce rubber synthetically, artisans originally made it from the latex of the rubber tree.
Green Revolution in Kingdom Plantae
History of Green Revolution
Toward the end of World War II Norman Borlaug, supported by the Rockefeller Foundation, began a series of genetic studies that led to the development of high-yield dwarf varieties of various grass grains. Eventually, the Food and Agricultural Organization of the United Nations expanded his work. They sent special varieties of wheat and rice to developing countries threatened by famine. The intense cultivation of those strains of agricultural staples dramatically increased food production in those regions. This program was so successful that they named it the green revolution. Food production in parts of Asia quadrupled following the green revolution.
Impact of Green Revolution on Kingdom Plantae
Along with the breeding of strains that possessed large grains was the need to support growth with heavy applications of fertilizer. Farmers generally derive these fertilizers from the processing of petroleum synthetically. They also used large amounts of pesticides. Unless the farmers applied great amounts of DDT and similar chlorinated hydrocarbon pesticides, droves of insects could destroy the crops either during growth or after harvesting and storing them in bins or silos. The green revolution has involved a total mobilization of machinery, chemicals, and human resources in achieving success.
Advantages of Green Revolution
Hybridization studies of wheat, rice, and corn continue in such places as the International Rice Research Institute in the Philippines and the International Maize and Wheat Improvement Center in Mexico.
