Write an essy on diversity of plants
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bySinghdeeksha8501 26.06.2018
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Alicia43
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DIVERSITY OF PLANTS Plants evolved more than 430 million years ago from multicellular green algae. By 300 million years ago, trees had evolved and formed forests, within which the diversification of vertebrates, insects, and fungi occurred. Roughly 266,000 species of plants are now living. The two major groups of plants...
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Biodiversity is the total variability within and among species of all living organisms and their habitats.
It is estimated that there are between 300,000 and 500,000 species of higher plants (i.e flowering and cone bearing plants), of which approximately 250,000 have been identified or described.
The diversity of plant life exists for many reasons - a key factor being adaptive changes which allow different species to thrive in the many varied environments of the world. Plants have developed adaptations for different soil types, methods of pollination, daylight hours, temperature, altitude, competition with other plants. The list is endless, even two plants of the same species, separated by geography will have a different genetic make-up.
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There are nearly 3, 92,000 species of flowering and non-flowering plants which have been identified.
Depicts details on the total number of plant species recorded so far and the number believed to exist on earth. The number of plant species that occur in India is more than 45,000, which represent nearly 12 percent of recorded flora of the world.
They range in size from microscopic bacteria, some of which are some thousandth of cm in diameter, to giant Sequoias which grow to more than loom, in height and may weigh more than 1000 tons. A giant Californian Sequoia may probably be more than 3500 years old. There are certain coniferous plants which are more than several hundred years old.
Plant form varies with varying environmental conditions. Plants that grow in dry areas and swampy areas vary distinctly. The same comparison can be made between plants found in tropical and polar climates.
The soil factors, wind conditions and the duration of sunlight also determine the forms of vegetation. For example, the sandy soil of coastal plains does not hold water very well. Thus, it can support plants whose leaves are much reduced or modified. But the broad-leaved trees grow better in the soil with more humus.
The origin of plants continues to be a debatable question. Fossil data indicate that the plants have originated nearly 2 billion years back.
In this long span of time, many plants have originated, many more evolved into complex, better adapted ones and still many unknown number who failed to evolve with time have become extinct. At present the large numbers of plants that surround us are the products of this evolutionary process.
The most primitive and the smallest plants in terms of their structural simplicity are the bacteria and algae. Bacteria are mainly known for the diseases they cause to humans and role played in decay and decomposition of organic materials.
The algae, on the other hand, are the simplest photosynthetic plants. However, the term algae do not refer to a single group of plants but to a multitude of its representatives who vary primarily on the basis of pigmentation, complexity of form and elaboration of process of reproduction.
Fungi like the algae are primitive on the scale of plant evolution. These are however, non chlorophylls plants and live as parasites or saprophytic ally on dead, decaying organic debris.
They seem to have an evolutionary development parallel with algae. Lichen is a dual organism, where an association is formed between algae and fungi. Some fungi are synonymous with plant diseases yet others are important in baking industry, alcohol production and in manufacture of antibiotics.
the common man is not familiar with these small inconspicuous diverse worlds of plants. To him the term plants refer to some familiar, green leafy land habiting organisms. However, land plants evolved considerably later in comparison to aquatic algae.
During this transition from water to land, it appears that evolution has occurred in two distinct lines. One of these was appearance of conducting or vascular tissues. These plants reached great degree of diversity in form and function. In second line, no specialized vascular or supporting tissues developed and these plants gave rise to no other new forms. Modern descendants of the latter are liverworts, hornworts and mosses. These are collectively called as bryophytes.
These are most primitive of green land plants, predominantly amphibious in habit. Individually, the bryophytes are small inconspicuous and often seen growing in clusters. The vascular plants which represent another line of evolution from the primitive aquatic plants are more than 400 million year old. Club mosses, horsetails, ferns form the conspicuous representative of this type of organisms.
These are closed seeded; they are now the dominating forms of plant life. They are not only the highest forms of plant life, but the most diversified and widespread, as well.
A brief survey of plant kingdom shows that some plants may lack roots, stems and leaves, others are non green, some do no, contain the supporting and conducting system Some do not form seeds, other have naked seeds and some plants have flowers, from winch.
Seeds with integument, called fruits develop. , the world of plants shows a great diversity in their life cycle pattern. The simplest and earliest forms have haploid plant bodies called thalli, i.e. the gametophyte or haploid or n phase is quite evident in the life cycle. However, saprophyte or diploid or 2n phase is only restricted to zygote or the fusion products of sexual reproductive unit.These diploid or saprophytic or zygotic phase is very Short lived and never becomes a free living plant at maturity. It undergoes meiosis or reduction division to produce the haploid, free living and independent phase.