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Monday, 13 August 2018

DISCUSS THE EVOLUTIONARY TRENDS IN BIOLOGY AS APPLIED TO PLANT AND ANIMALS


INTRODUCTION 

The theory of evolution explains the diversity of life on earth today by the descent of each and every species from common ancestors. The study of evolution should lead us back to a first form of life from which all others have been descended. What was this first form? We do not know, and the best we can do is to make intelligent guesses about its characteristic. Where did it come from? We do not know the answer to this question either although every thoughtful person has probably wondered about it at one time or another.


THEORIES OF THE ORIGIN OF LIFE 

Among the first attempt at answering this question in our civilization were the stories of creation that are found in the bible other cultures, too, have their stories of the creation of life. These stories share two features in common. First, they were created long before man had gained any knowledge of the physical, chemical, and biological principles that are the basis of life. Second, they invoke divine intervention in the creation of life and thus fall outside the scope of scientific inquiry.


THE COSMOZOA THEORY

This theory of the origin of life does fall within the scope of scientific inquiry. It explains the presence of life on our earth by assuming it was brought here from elsewhere in the universe.


THE THEORY OF SPONTANEOUS GENERATION

As move was learned about biology, however, men began to doubt the possibility of spontaneously generation in 1668 the Italian physician Francesco Redi performed an experiment to show that maggots do not arise spontaneously in decaying meat but are produced from the eggs of flies. Although the spontaneous generation of large forms of life began to be doubted after this. Van leenwenhock’s discovery of microorganisms  reopened the question.


OPARIN’S THEORY

While conceding that life does not arise spontaneously now, oparin felt that it might well have arisen spontaneously under the conditions that existed earlier in the history of the earth.


THE DAWN OF LIFE

No one knows exactly when life first appeared on the earth. We would not expect the first forms of life to leave fossil remains for us. However, fossils that resemble algae have been found in rocks over three billion years Old. Nourishment for the first form of life was no problem. Surrounded by the same soup of organic molecules from which it arose, it had only to use these molecules by that the first living organism secured its energy from these organic molecules.


THE EVOLUTION OF THE PROTISTS

Geology tells us very little about the evolution of protists only those with hard parts e.g. (foraminifera, din toms) leave satisfactory remains. The best we can do is to work intelligent geneses about their evolutionary relationships on the basis of the study of modern forms .however, the photosynthesizing organisms which h must have evolved from it may possible be still represented today by the green photosynthetic bacteria. These organisms live on the surface of ocean mud and, like the purple sulfur bacteria. Photosynthesis by these organisms would have liberated oxygen into the atmosphere and thus established the conditions for the evolution of aerobic, respiring organisms. The blue-green algae were the descendants of the green sulfur bacteria first to use water in photosynthesis.
The red algae, too, may have been among the first photo synthesizers to release oxygen into atmosphere. Although present members of the phylum are considerably more complex than the blue-green algae. The presence of oxygen in the atmosphere opened the way for the evolution of the aerobic, heterophic bacteria. Many of these move by means of a simple flagellum which resembles one of the central fibrils of the multistrandel cilia. At the same time, chemoautotrophic bacteria, such as the colorless sulfur bacteria.


EVOLUTION TRENDS IN PLANTS

THE FIRST VASCULAR PLANTS

Although the anatomy of the first plant is not entirely dear, we are confident that they belonged to phylum tracheophyta and were more or less adapted to life on land. By the Devonian period, four distinct groups had appeared, each of which has left some descendant right up to the present time. These groups were the psilopsida, lycopsida sphenopsida and pteropsida. The psilopsida like their modern descendant psilotum, had no root or leaves. They did, however, have both underground stems (rhizomes) and erect stems and these also produced the sponrangia. The photosynthesis pigment were surely chlorophyII a and b. from a study of psilotum, we deduce that they product only one kind of spore, and these developed into tiny gameto phytes which in turn, produced both antheridia and archegonia fertilization was by swimming sperm and hence these plants must have been restricted to habitats which were quite wet, at least some of the time. Both the lycopside and sphenoswids had roots and leaves, each containing xylem  and philoem tissue connected with that of the stem. The leaves were simple and small, all their vascular tissue occurring in just a single, unbranchedvein.
Some of the lycopsids produced not one but two kinds of spores.
The first pterosids, the ferms, also contributed a large array of species to the flora of the Devonian landscape. Unlike the members of the other subphyla veins. Like most of our temperate climate ferms of today, they were homosporous, that is, only one kind of spore was produced each fern spore, develop into a prothallus that bears both male and female sex organs. Fertilization requires moisture in which the climate sperm can swim to the egg. Fossil remains from the Devonian indicate that some early fern like plant were heterosphorous, that is, they seed ferns as these plants are called, were among the earliest of the gymnosperm, another class in the subphylum pteropsida.


THE MOSSES AND LIVERWORTS

The nonvascular plants have sometimes been considered the ancestors of the vascular plants. Their simplicity of structure, lack of vascular tissue and restriction to dump location do suggest that they are intermediate forms between the algae and the vascular system and woody tissue and the necessity for surface water in which the sperm can swim from antheridia to archegonia have limited the evolutionary potentialities of these organisms.


THE ANGIOSPERMS

The angiosperms are found in practically every habitat. Although they incorporate a variety of features that enable them to live even in arid location, some have returned to an aquatic existence. The possession of roots permits the extraction of moisture and minerals from beneath the surface of the land. Roots also save to anchor the plant against the wind. The presence of a cambium capable of producing woody tissue provides for the support, high in the air of need be, of leaves and flowers. Xylem and ploemenable water, foods and hormones to be translocated long distance in the plant quickly. A waxy inticle on leaves and herbaceous stems and the lork on woody stems prevent rapid loss of water from the plant by evaporation. The angiosperms share with the gymnosperms the characteristics of retaining the female gametophytes within the megasporagium in the gymnosperms and some angiosperms, the polen grains are simply brown from plant by the wind. Many other angiosperms attract insect or other animals by power  and thus exploits the animals power of locomotion to aid cross- pollination.




REFERENCES

Oparin A.I., The origin of life, Dover publication, Inc., New-York, 1953.
Wald G., the origin of life” scientific American, Reprint No. 47, August, 1954
Brown, H., the Age of the solar system scientific American, Reprint No. 102, April. 1957.
Clark  J.D. “ Early Man in African”, scientific American, Re       print No. 820, July, 1958
Broom, R., “The Ape-Men”, scientific American, Reprint No. 832, November, 1949.
Howells, W., Mankind in the Making, 2nd editor, Editions, New-York 1961.
Roomer, A. S. the vertebrate story University of Chicago press, Chicago, 111, 1959.
Napier, J. the Evolution of the Hand, scientific Americanhhhhhhhhh Hand, scientific American, Reprint No. 140, December, 1962


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