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Here is a term paper on the ‘Origin of Life’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short term papers on the ‘Origin of Life’ especially written for school and college students.
Term Paper on the Origin of Life
Term Paper Contents:
- Term Paper on the Introduction to the Beginning of Life
- Term Paper on the First Cells
- Term Paper on the Evolution of Energy Systems
- Term Paper on the Evolution of Eukaryotes
- Term Paper on the Classification of Organisms
- Term Paper on the Binomial System of Naming Living Things
- Term Paper on What is a Species?
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Term Paper # 1. Introduction to the Origin of Life:
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Darwin believed that it would probably be impossible ever to look back down that long corridor of time and reconstruct life’s beginnings.
Until very recently, the earliest fossils known were those of the Cambrian period, a mere 600 million years ago, and for a long time after the publication of The Origin of Species, biologists regarded the earliest events in the history of life as chapters that would probably remain forever closed.
Two scientific developments, however, have greatly improved our long-distance vision. One was the formulation of a testable hypothesis about the events preceding life’s origins; the second was the discovery of cells more than 3 billion years old.
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The testable hypothesis was offered by the Russian biochemist A. I. Oparin. According to Oparin, the appearance of life was preceded by a long period of what is sometimes called chemical evolution.
During this period, which occupied almost a third of the earth’s history, there was little or no free oxygen in the atmosphere surrounding the earth, and the oxygen that was present existed mainly in the form of water vapor.
The atmosphere was a reducing one-an atmosphere that abounded in hydrogen gas, methane (CH4), ammonia (NH3), and other carbon-hydrogen gases. As we have seen, combinations of these four elements available in the primitive atmosphere-hydrogen, oxygen, carbon, and nitrogen-make up to more than 95 percent of living tissues.
Energy was required to break apart the simple gases of the atmosphere and re-form them into organic molecules. And energy abounded on the young earth. There was heat energy, both boiling (moist) heat and baking (dry) heat.
Water vapor spewed out of the primitive seas, cooled in the upper atmosphere, collected into clouds, fell back on the crust of the earth, and steamed up again. Violent rainstorms were accompanied by lightning, which provided electrical energy. The sun bombarded the earth’s surface with high-energy particles and ultraviolet light and radioactive elements within the earth released their energy into the atmosphere.
Oparin hypothesized that under such conditions organic molecules were formed and collected in a thin soup in the earth’s seas and lakes. Some of these molecules might have become locally more concentrated by the drying up of a lake or by the adhesion of the molecules to a solid surface.
In the 1950s, Oparins hypothesis was tested in the laboratory by Stanley Miller, then a graduate student at the University of Chicago. Miller showed that under conditions simulating those believed to have been present some 3 to 4 billion years ago; amino acids are produced from hydrogen gas, ammonia, methane, and water vapor.
Miller’s experiments have now been repeated many times in other laboratories. With various modifications in the experimental conditions, almost all of the common amino acids have been produced and also purines, pyrimidine’s, ribose, and nucleotides.
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As the concentrations of such molecules increased, it is not difficult to imagine that they would have assembled themselves in aggregates, held together by hydrophobic interactions, hydrogen bonds, and other/weak forces.
The most stable of the chemical combinations would have tended to survive, and hence a form of natural selection played a role in chemical evolution as well as in the biological evolution that was to follow.
At some stage in chemical evolution, a boundary or membrane formed around such an aggregate of macromolecules, permitting it to lead a separate existence from its external environment. What was enclosed in that boundary membrane? A catalytic protein? A self- replicating nucleic acid? Such questions lead directly to the mystery of the origin of the genetic code.
As far as we can see, there is no underlying molecular logic to the code, no reason why a particular triplet should specify one amino acid rather than another. Did the code come into being purely by chance? It would appear so.
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All we know for sure is that all living systems are the descendants of these tiny metabolizing droplets.
Term Paper # 2. The First Cells:
When did life begin? We will probably never be able to answer this question because it depends first on how we define life and, second, on finding chemical traces probably long since erased. We can establish some sort of time scale, however, owing to the discovery little more than a decade ago of microfossils in flint like rocks, called chert, in South Africa.
The fossils, whose structure is visible only by electron microscopy, resemble present-day bacteria and blue-green algae. The rocks, in which they were found, according to radioactive dating, are 3.4 billion years old. Thus life began very early, perhaps in the first billion years of earth’s history.
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Term Paper # 3. The Evolution of Energy Systems:
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Although both heterotrophs and autotrophs are represented among the earliest microfossils, it is logical to postulate that the first living cell was an extreme heterotroph. It probably possessed few enzymes, compared with a modern cell, and so was capable of only a few anabolic reactions. It would have had to find most of the molecules it required in Oparins organic soup.
As the primitive prokaryotic heterotrophs increased in number, according to this hypothesis, they began to use up the complex molecules on which their existence depended and which had taken millions of years to accumulate. Competition began.
Under the pressure of this competition, cells that could make efficient use of the limited energy sources now available were more likely to survive than cells that could not. In the course of time, cells evolved that were able to synthesize organic molecules out of simple inorganic materials. Without the evolution of these autotrophs, life on earth would soon have come to an end.
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The most successful of the autotrophs were those that evolved a system for making direct use of the sun’s energy-the process of photosynthesis. With the advent of photosynthesis, the flow of energy in the biosphere came to assume its modern form: Radiant energy channeled through photosynthetic autotrophs to other forms of life.
With the evolution of photosynthetic cells that produced oxygen, the atmosphere slowly began to change. As a result of photosynthesis, the concentration of oxygen in the atmosphere rose to 1 percent about 600 to 1,000 million years ago and to 10 percent only about 400 million years ago.
The present concentration of 21 percent oxygen has been created and is maintained by photosynthesis. The accumulation of oxygen in the air made possible, in turn, the evolution of organisms that produced most of their chemical energy by cellular respiration.
According to this hypothesis, in terms of energy production, anaerobic glycolysis came first, followed by photosynthesis and finally, as oxygen accumulated, by respiration. The genetic code was determined and the pathways of glycolysis, respiration, and photosynthesis were established in nearly their present form long before the appearance of any eukaryotic cells.
Term Paper # 4. The Evolution of Eukaryotes:
The microfossil record indicates that the eukaryotes probably evolved about 1.6 billion years ago. Eukaryotes, are distinguished from prokaryotes by their larger size, the separation of nucleus from cytoplasm by a nuclear envelope, the organisation of their DNA, and their complex organelles, among which are chloroplasts and mitochondria.
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The step from prokaryotes to the first eukaryotes was one of the big evolutionary transitions, second only to the origin of life. The question of how it came about is a matter of current and lively discussion. One interesting hypothesis is that larger, more complex cells evolved partly as a result of certain prokaryotes’ taking up residence inside other cells. (Such a close association between two organisms of different species is known as symbiosis.)
As oxygen gas began slowly to accumulate in the atmosphere, those bacteria that were able to convert to the use of oxygen in ATP production gained a strong advantage, and so such forms began to prosper and increase. Some of these evolved into modern forms of bacteria. Others, according to this theory, became symbionts within larger cells and evolved into mitochondria.
Several lines of evidence support the hypothesis that mitochondria are descended from specialised bacteria: Mitochondria contain their own DNA, and this DNA is present in a single, continuous (“circular”) molecule, like the DNA of bacteria; many of the same enzymes contained in the cell membranes of bacteria are found in mitochondrial membranes.
The ribosomes of mitochondria resemble those of bacteria both in their size (they are smaller than those of eukaryotic cells) and in some details of their chemical composition; mitochondria appear to be produced only by other mitochondria, which divide within their host cell. (However, to make the situation more complex, there is nowhere near enough DNA in mitochondria to code for all the mitochondrial proteins. Host- cell DNA is also required for mitochondrial structures.)
We know little about the original cells in which these bacteria first set up housekeeping-or, indeed, if they actually existed. But if they did exist, they probably had no means of using oxygen for cellular respiration and so were dependent entirely on anaerobic fermentation as an energy-releasing process, which, as we have seen, is relatively inefficient.
Cells with respiratory assistants would have been more efficient than those lacking them and so would have out reproduced them.
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In an analogous fashion, photosynthetic prokaryotes ingested by larger, non-photosynthetic cells are believed to be the forerunners of chloroplasts. By this symbiosis, the smaller cells gained nutrients and protection, and the larger cells were given a new energy source.
This hypothesis accounts for the presence in eukaryotic cells of complex organelles not found in the far simpler prokaryotes. It gains support from the fact that many modern organisms contain intracellular symbiotic bacteria and algae, indicating that such associations are not difficult to establish.
Modern one-celled eukaryotes-the protists-are a very diverse group, most of which probably bear little or no resemblance to the first eukaryotic cells.
The multicellular organisms are all eukaryotes. The major groups- the fungi, the plants, and the animals—are believed each to have originated from one (and possibly more) separate types of one-celled eukaryotes.
There is no fossil evidence of their origins. The first fossils of multicellular organisms are found in sediments a mere 0.6 billion years old, and their diversity and complexity indicate that eukaryotes had been in existence for millions of years.
If we measure out the history of the earth on a 24-hour time scale, the oldest known fossils appeared at 6 A.M., the oldest eukaryotes between 4 and 5 P.M., the first multicellular organisms between 8 and 9 P.M., and Homo sapiens in the last 30 seconds at 11:59:30 P.M.
Term Paper # 5. Classification of Organisms:
As late arrivals on the evolutionary scene, we humans are confronted with a bewildering variety of living things. As many as 5 million different kinds of organisms share the biosphere. For thousands of years, we have been trying to find order and meaning in this diversity. Systematics are biologists who study this order, and taxonomists arrange organisms in systems of classification.
Aristotle is generally considered to be among the first to have tried to group organisms in ways that made sense. He recognised, for example, that you could not choose any single characteristic as the basis for grouping. For instance, suppose you decided to group all the animals into those that fly and those that do not.
You would end up with one category that included most insects, birds, and bats, and you would have to separate some obviously close relations, such as the winged and the wingless ants that occur as members of the same colony. Aristotle recognised, as do modern taxonomists, that one had to look not just at a single feature but at many characteristics of a plant or animal.
On the basis of overall similarities and differences, an organism could be placed with other forms in increasingly restricted categories- vertebrate, bird, duck, and mallard for example.
In the middle of the seventeenth century, an English clergyman, John Ray, set out to catalog all the organisms in the world and to arrange them systematically. He was the first to use the word species to describe a kind of organism.
A species, according to Ray, was made up of organisms that were morphologically the same-from morphe, meaning “shape” in Greek-and that could reproduce their own kind.
Ray cataloged all the plants in the vicinity of Cambridge, the first complete catalog of one locality ever to be made. Then, traveling through England and the Continent, he worked his way, astonishingly, through all the plants that he could learn about (almost 19,000) and the birds, the fishes, and the four-footed animals.
At the time of Ray, and for a number of years thereafter, plants and animals were designated by cumbersome phrase names, or polynomials. These polynomials were brief descriptive phrases concerning the plant or animal to which they were applied.
The first word in the polynomial had come, by the close of the seventeenth century, to designate the genus (plural, genera), an inclusive group of similar species. Thus, the numerous kinds of roses were grouped in the genus Rosa, many butterflies in the genus Papilio, and cats and catlike animals in the genus Felis.
Term Paper # 6. The Binomial System of Naming Living Things:
The system of naming living things was simplified by the eighteenth- century Swedish professor, physician, and naturalist, Carolus Linnaeus. (Linnaeus was born Carl von Linne but latinized his name in the scholarly fashion of his time.) His ambition was to classify all the known kinds of plants and animals according to their genera.
In 1753, he published a two-volume work, Species Plantarum (“the kinds of plants”), which contained brief analytical descriptions of every species of plant known to European science. Although he used the polynomial designations and regarded them as the proper names for species, he made an important innovation.
In the margin of his book, opposite the “proper” name of each species, Linnaeus entered a single word, which, together with the generic name, formed a convenient “shorthand” designation for the species. In the book, catnip, which had previously been designated by the polynomial Nepeta floribus interrupte spicalus pedunculatis (“Nepeta with flowers in an interrupted pedunculate spike”), was described under Nepeta, and cataria was put in the margin, making it Nepeta cataria, which is its name today.
The convenience of this system was quickly recognised, and Linnaeus and subsequent authors soon replaced all “proper” names with “shorthand” ones. This binomial (“two-name”) system is still used today. A species name, as we have seen, consists of two parts-the generic name and the specific epithet (adjective or modifier).
However, a genus name may be written alone when one is referring to members of the entire group of species making up that genus, such as Drosophila or Paramecium.
A specific epithet is meaningless when written alone, however, because many different species in different genera may have the same specific epithet. The domestic dog is Canis familiaris, for instance; familiaris is a commonly used specific epithet and by itself would not identify any organism.
For this reason, the specific epithet is always preceded by the genus name, or, in a context where no ambiguity is possible, the genus name may be abbreviated to its initial letter. Thus Canis familiaris may be designated C. familiaris.
Term Paper # 7. What is a Species?
Species in Latin simply means “kind,” and so species, in the simplest sense, are the different kinds of organisms. A more technical definition of species is “a group of interbreeding organisms that do not ordinarily breed with members of other groups.” This definition conforms to common sense. If one species interbred freely with other species, it would no longer represent a distinct kind of organism.
This definition, although useful for animals, is not so useful for other organisms, such as some bacteria and protists that do not breed at all, as far as is known, and for some plants in which fertile crossings can take place among very different kinds of plants.
A profound change occurred in the concept of species with the acceptance of evolutionary theory. Rather than being the immutable, ideal form conceived by Linnaeus, a species is now seen to change constantly in both time and space.
However, even though a precise definition of species is elusive, the term is understandable in a practical way. For instance, anthropologists point out that primitive peoples, particularly hunter-gatherers, are able to recognise, distinguish, and name great numbers of the organisms with which they come in contact.
What these people, operating on a practical level, recognise as a “kind”-something different enough to have its own name-almost always coincides with what scientists recognise as a “species.” So despite the inability of experts always to agree upon a definition (or the organism to conform to one), the species is a clear and useful reality.
