Here is a compilation of essays on ‘Biosphere’ for class 5, 6, 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Biosphere’ especially written for school and college students.
Essay on the Biosphere
- Essay on the Origin of Biosphere
- Essay on the Fossil of Biosphere
- Essay on the Chemical Basis of Biosphere
- Essay on the The Geological Evidence of the Biosphere
- Essay on the Changing Environmental Conditions Associated with Glaciations of Biosphere
- Essay on the Diversification of the Biosphere
Essay # 1. Origin of Biosphere:
Biological organisms come in a wonderful variety of sizes, shapes and complexity. Besides providing us with the food, shelter and oxygen—essentials for life, the living creatures with which we share the planet give us pleasure in their bright colours, lively songs and graceful movements.
All living organisms of the earth, as noticed today, evolved through ages in this planet using solar energy and matter from the environment to build organized structures and to carry out the dynamic processes that define life sensing and responding to external stimuli, maintaining internal identity, integrity and re-productivity.
Every organism is a chemical factory that captures matter and energy from its environment and transforms them into structures and processes that make life possible. Matter consists of unique chemical forms—elements, molecules and compounds. Organisms use some elements in abundance, some in trace amounts and others not at all.
Certain substances are hoarded within cells, while others are actively excluded. Carbon is particularly important because chains and rings of carbon atoms form the skeletons of organic compounds, the material of which biomolecules, and, therefore, living organisms are made.
The tour major categories of bioorganic compounds—carbohydrates, proteins, fats and nucleic acids—constitute the basic material for life. These compounds organized in a proper fashion to constitute the structural and functional units of living organisms i.e., cells.
Microscopic organisms—such as bacteria, some algae and protozoa—are composed of single cells. But higher organisms are multicellular, usually with many different cell varieties.
Every cell is surrounded by a thin but dynamic membrane of lipid and protein that receives information about the exterior world and regulates the flow of materials between the cell and its environment. Inside, cells are subdivided into tiny organelles and subcellular particles that provide the machinery for life.
All of the chemical reactions required to create these various structures and provide them with energy and materials to carry out their functions, dispose of wastes, and perform other functions of life at the cellular level are carried out by a special class of proteins called enzymes.
A steady influx of solar radiation provides the heat and light energy needed to support life in the biosphere. Water, which covers approximately three-fourth of the earth’s surface, is readily available to life forms.
Because of its unique characteristics, it stabilizes the biosphere temperature and provides the medium in which life processes occur. The earth’s atmosphere provides gases necessary for life, helps maintain surface temperatures, and filters out dangerous radiation.
The population of different species that live and interact within a particular area make up biological communities. The interactions of a community with the physical factors of its environment comprise that ecosystem level of organization and study.
Matter and energy are processed through the tropic levels of an ecosystem via food chains and food webs. Thus biosphere is a source of large quantities of essential elements, and in a given ecosystem these elements are constantly used and reused by living organisms (Fig. 3.1).
Essay # 2. Fossil of Biosphere:
(i) Ancestral Life Forms:
In order to trace and to understand the evolutionary process by which we believe living systems arose on earth, it is quite essential to know the early life forms of earth surface, i.e., the fossil remnants of the past life forms.
The fossil record, consisting of remains or impressions of organisms which have been preserved in the earth’s crust, tells us something about the types of organisms present at specific times during the past history of the earth.
Fossils are date by determining the age of the rock strata in which they are found. This is often done by a technique called “Radio isotope dating” technique. The decay rate of a radioactive element is so predictable that it can be used as a basis for determining the age of a substance, and the rubidium-strontium system has been employed extensively in geology to date rock samples.
Earth crust is constituted of a variety of rocks, which are formed in a number of ways. Of course, most fossils are found in sedimentary rocks.
The history of the earth is divided into four major eras as per the age of the rocks:
The Precambrian, Paleozoic, Mesozoic and Cenozoic era. The oldest fossils have been found in Precambrian rocks about 3.2 billion years ago. These fossils include a variety of microscopic organisms and organic materials.
(ii) Atmosphere of the Primitive Earth:
Although there are not sufficient geochemical data to provide us with a precise and conclusive description of conditions prevailing on the surface of the primitive earth, it is possible to construct some reasonable models by drawing on a large amount of available circumstantial evidence. It is considered that the earth was formed from a turbulent cloud of cosmic dust and gases.
During the initial stages of the aggregation of material forming the earth, volatile compounds like Carbon, Nitrogen, Hydrogen, Oxygen and Sulphur must have been retained by the dust particles in non-volatile form. In later stages of aggregation, the compression of material as well as the decay of radioactive elements resulted in the production of large amount of heat, which eventually melted the interior of the earth.
The formation of the primitive atmosphere was a result of outgassing from the earth’s interior, largely due to volcanic activity.
As the temperature of the earth’s interior rose, the non-volatile compounds of Carbon, Nitrogen, Hydrogen, Oxygen, and Sulphur were pyrolyzed to a mixture of NH3, N2, H2, CH4, H2O, CO, CO2 and H2S. Although we do not know the exact composition of the primitive atmosphere, it undoubtedly had reducing properties (perhaps lack of O2).
Simple organic compounds were synthesized from the mixture of atmospheric gases with the aid of energy sources on the primitive earth. These included ultraviolet radiation, electric discharges, heat from volcanoes, radioactivity, cosmic rays, and shock waves.
Organic compounds accumulated in the ocean, which has become referred to as the “primitive broth“. It is thus generally assumed that life originated in the oceans from these organic compounds.
(iii) Early Life Forms of Biosphere:
The transition from molecules to cells is a process about which reasonable men disagree. The available data are meager and subject to a wide variety of interpretations. Clearly much work is needed before we can say that we understand how cellular entities enrolled.
Since the atmosphere of the earth probably lacked free oxygen, it seems reasonable to assume that the first cells were anaerobic heterotroph—they existed in the absence of oxygen and depended for survival on organic compounds synthesized by abiotic means.
Gradually, they evolved an increased ability to synthesize organic molecules from precursors available in the environment. As long metabolic pathways on the cells evolved, cells became less dependent on the environment for supplies of nutrient compounds.
The evolution of these pathways was favoured by natural selection, since a cell that evolved the capacity to synthesize any necessary compound could survive without obtaining that compound as a nutrient from the environment and hence, possessed a competitive advantage over metabolically less versatile cells.
One of these metabolic innovations that eventually evolved was the ability to degrade glucose and to use the energy released in the process to form ATP.
A particularly significant metabolic breakthrough was the appearance of anaerobic autotrophs, some species of chemosynthetic bacteria and a wide range of photosynthetic prokaryotes. Photosynthesis endowed organisms with the ability to use the energy of solar radiation (light) to produce “energy-rich” ATP.
Some of these photosynthetic organisms produce molecular oxygen as a by-product of the photosynthetic process. Oxygen productivity by photosynthetic prokaryotes—some of which resemble modern forms of blue-green algae—were probably firmly established as early as 2.7 billion years ago, shortly before the beginning of the Middle Precambrian.
The establishment of oxygen-producing photosynthesis had far reaching effects. Eventually, the atmosphere of the earth became drastically changed as a result of the release of free oxygen into the air.
As oxygen accumulated in the atmosphere is a by-product of photosynthesis, anaerobic prokaryotes that were not capable of surviving in the presence of O2 were eliminated or were restricted to local environments that lacked oxygen.
Facultative anaerobes, anaerobic organisms capable of living in either the absence or presence of free O2, probably became widely distributed. When the oxygen concentration in the air reached high levels, aerobic heterotrophs and aerobic autotrophs became the dominant types: these organisms required oxygen for survival.
This scheme is supported by the wide range of metabolic types found among present day prokaryotes. These include heterotrophs; autotrophs, some of which produce O2 as a by-product of photosynthesis and some of which do not; strict anaerobes; facultative anaerobes, & strict aerobes.
About 1.5 billion years ago, eukaryotic cells arose in some unknown way, probably from prokaryotic ones. By the time eukaryotic cells appeared, it is probable that all the basic metabolic patterns now found in present-day cells had already evolved.
These eukaryotic cells, aerobic and hence adapted to survival in an oxygen-containing environment, became the structural unit of all autotrophic and heterotrophic multicellular forms.
Essay # 3. Chemical Basis of Biosphere:
The question of the origin of life re-vented from the scientific to the philosophical realms, a position it still holds in the minds of many.
In the twentieth century, Alexander Oparin (1924) and J.B.S. Haldane (1929) proposed that life originated as an interaction between organic compounds formed under the anoxic conditions that prevailed on the early earth. After these proposals were published, some scientists began to consider the question of the origin of life as an experimental problem.
Miller’s (1953) pioneering discovery of the early and rather rapid formation of amino acids from inorganic precursors ushered in a new field of laboratory science referred to as “Primitive-Earth-Model Experiments”, “Prebiotic Chemistry” or “Experimental Chemical Evolution“.
From a source of Carbon, Hydrogen, Oxygen, Nitrogen & Energy—Hydrocarbons, Fatty acids. Benzene & Phenolic compounds, Amino acids, and many other familiar organics may be easily produced in the laboratory, enhance confidence in the hypothesis that life arose from cosmic constituents under anoxic conditions.
In fact, the organic compounds found in meteorites are quite similar to those produced in simulation experiments.
Although there is no unanimity about the source of energy for organic compounds formation, it is generally conceded that the Archean ultraviolet radiation flux at the Earth’s surface prior to the accumulation of atmospheric O2 was probably the major source of energy, both for prebiotic organic synthesis and for early biological processes such as the induction of lysis and transduction by bacteriophage.
The problem of the production of organic components of small molecular weight seems more or less solved, but how was organic matter aggregated?
How were monomers polymerized. How was the information transmitted to new aggregations of organic matter and reliable heritability established? The gap between the most complex mixture of organic chemicals and the simplest cell is still to be crossed in theory and in the laboratory.
The linking of amino acid residues into polymers including both peptide and non-peptide linkages has been reported to occur under conditions presumed of the early earth. The mechanism of the spontaneous as opposed to enzymes mediated, formation of polypeptide and nucleotide polymers from monomers is a mystery.
All life, using the same basic membrane-wrapped machinery of nucleic-acid-determined protein synthesis, reproduces with incredible fidelity. Although the question of how the first bacteria formed from aggregates of organic compounds cannot be answered yet in details, but it is assumed that prokaryotes evolved extensively by direct filiation in the primitive earth.
The earliest microbes were heterotrophs reproducing in environments supplied with abiotically produced nutrients and minerals. The autotrophs were details from these heterotrophs after the evaluation of 0, on the earth surface. The conspicuous forms of life today require O2, to live. The eukaryotic cells are derived from the prokaryotes in course of time.
Although life is patchingly distributed, a veritable scum that reaches mainly to within a meter of the Earth’s watery or solid surface, it extends over an area of about 500 million square kilometers.
The next advance in the expansion of life may be above the troposphere to the stark cold reaches of the rest of the solar system and perhaps, beyond. But we should be warned; for its own survival, life must moisten and modify its environment.
Without maintaining species diversity, the capacity for rapid reproduction, interactions, flexibility and redundancy, life will not maintain itself. That life can survive in space has been amply demonstrated, but survival is not reproduction. Whether the biosphere will ever expand into space is surely an open question.
Accumulation of Organic Material and Formation of the First Cell:
A precondition to any form of biological evolution requires the accumulation of organic material and formation of the cell. There are at least two contrasting theories as to how organic matter accumulated in the prebiotic environment: terrestrial accretion and commentary in fall.
The oldest and most widely cited theory is that of terrestrial accretion.
This theory, first proposed by Miller in 1953, is based on the principle that, under laboratory conditions, when gases such as hydrogen, carbon dioxide, methane, and ammonia are heated with water, and energized by electrical discharge for at least 24 hours, approximately half the carbon originally present in the methane gas will be converted into amino acids, sugars, and other organic molecules, including purines and pyrimidine’s (required to make nucleotides).
Amino acids and nucleotides can associate to form polymers including polypeptides (proteins) and polynucleotides (RNA and DNA) thus forming the first building blocks of the cell. An alternative theory is that the first organic material on Earth came from other planets and entered the Earth’s atmosphere via meteoritic input. This idea was originally viewed as better suited to the realms of science fiction.
However, there is increasing evidence to support the theory that meteoritic and commentary in fail provided the first organic material on Earth, analysis of the present day meteorites on the ice beds of the Antarctic (carbonaceous chrondrites), for example, indicate that they typically contain between 1 and 4% carbon, mainly as graphite but also as much as 1% organic molecules.
Organic compounds contained within the carbonaceous chrondrites include hydrocarbons, amino acids, carbon, hydrogen cyanide and amphiphilic molecules.
Another crucial event in the formation of the first cells would have been development of the outer cell membrane, since without this there would be no means of simple containment of the macromolecules within the cell. There is also the question of how organic compounds become sufficiently concentrated to form more complex molecules.
An extremely important environment for both processes to occur would have been shallow tidal pools, where cycles of solar heating and cooling, combined with tidal wetting and drying, would have provided the necessary conditions for concentration and molecular self-assembly.
Essay # 4. The Geological Evidence of Biosphere:
Of all the organisms presently on the Earth, prokaryotes are the simplest in structure, smallest physically, and most abundant in terms of number of individuals.
They range between approximately 1 and 10 pm in size, are single celled (although many types have cells joined together within a mucilaginous sheath), lack an organized nucleus surrounded by a nuclear envelope, and reproduce by binary fission (i.e. each cell increases in size and divides into two).
Prokaryotes also tend to have one of three basic cell shapes:
A straight rod shape (bacilli); a spherical shape (cocci); or a long, coiled shape (spirilli).
Fossil microorganisms have also been extracted from other early sedimentary deposits, including cherts and shales. Some of the earliest examples are found in the Warrwoona Group in Western Australia, where filamentous and colonial fossil structures have been reported from carbonaceous cherts dated between 3500 and 3300 Ma.
These fossils, which are predominantly small spheres and filaments, indicate close morphological comparison with extant prokaryotes, based on both cell size and also structure (i.e., whether single cells or in colonies, whether the colonies are sheath enclosed, etc.).
The microorganisms contained within the Warrwoona Group sediments have therefore been -classified as photoautotrophic cyanobacteria (oxygen-producing blue-green algae) and taken to indicate the presence of organisms capable of oxygen-producing photosynthesis as far back as 3500 million years ago (early Archaean).
Cell size and structure have not been the only factors used to identify these early microorganisms as prokaryotes; evidence of their reproductive mode has also been discovered. There are now many examples in the early fossil record of cells that have been preserved while in a state of cell enlargement and division, suggesting binary fission.
Evolution of the Eukaryotes:
Eukaryotes differ from prokaryotes in that they have a membrane-bound nucleus in which the DNA is contained, organelles including mitochondria, integrated multi-cellularity, and sexual reproduction (sometimes).
They constitute the three major groups of multicellular organisms (plants, animals, and fungi), along with many groups of the Protista, including species of red, green, and brown algae. Because of the diversity and importance of eukaryotic organisms to life on Earth, it is often stated that the evolution of eukaryotes was one of the most important events in the history of life.
Evidence for eukaryotes (from fossil organisms and ancient biomolecules) suggests that they were probably present on Earth from as early as 2700 Ma.
Three records of early eukaryotes of particular interest to the evolution of plants include the oldest recorded alga Grypania, dated to 2100 Ma, fossil bangiacean red algae, dated to approximately 1200 Ma, and cladophoralean green algae, dated to between 800 and 700 Ma.
Possible Triggering Mechanisms of Eukaryotic Evolution:
A number of researchers have suggested that the combined geological/molecular record demonstrates a general trend of episodic increases in biological diversity through the Archaean and Proterozoic (~ 3500-540 Ma).
Six major biological events, which are specific to the plant fossil record are recognized including:
(i) the origin of life on Earth and diversification of anaerobic archaebacteria and eubacteria at or around 3500 Ma;
(ii) origin of photosynthetic organisms around 3300 Ma;
(iii) the appearance of organisms capable of aerobic metabolism and cellular acquisition of the organelles mitochondria and, later, chloroplasts, between 2800 and 2400 Ma;
(iv) the appearance of complex eukaryotic organisms in the geological records from approximately 2100 Ma;
(v) the large increase in diversity of organisms and radiation of acritarchs—a group of organic- walled microfossils, the majority of which are though to represent reproductive cysts of green algae oral-age cysts, from approximately 1000 Ma;
(vi) the large increase in diversity of planktonic algae from approximately 540 Ma.
Evolution of Life Forms through Ages:
Over the years in the geological part, the Earth’s geomorphology, climate and biotic community changed gradually. In early Palaeozoic, some 540 million years ago, three separate land masses existed: Asia, North America and Europe, and Gondwanaland (which includes present day Africa, South America, Australia New Zealand and Antarctica, etc.).
During the Palaeozic, 420 million years ago, North America and Africa lay close together around the south pole and the rest of Gondwanaland lay on the far side of the south pole, pointing towards the equator.
Slowly the land mass moved northward, so that by the Carboniferous age, 340 million years ago, the whole of Africa had moved across the south pole and Antarctica lay in the region of the south pole. During the Permian, these three blocks joined, forming a single land mass Pangaea, which further moved northward, and began to break apart slowly by mid-Mesozoic age.
By the mid-Cretaceous, about 100 million years ago, Africa and South America had split apart Thus by the end of the Cretaceous, Gondwanaland had broken up, the only intact land mass was North America —thus, collectively known as Laurasia.
Until the lower Eocene, Laurasia remained intact. North America was connected to Europe by Greenland and Scandinavia. But in the mid-Eocene, the North Atlantic joined the Arctic Ocean, separating Laurasia into North America and Europe.
The formation, breakup and northward drift of continents resulted in broad climatic changes and the formation of geological barriers that affected evolving plant and animal life. Between 2,700-2,000 million years ago, prokaryotes developed, but eukaryotes evolved sometime later. The Precambrian era came to a close with the sudden rise of Metazoa.
The Palaeozoic saw the evolution of the earliest known fish, the first amphibians, the first reptiles, the first insects and the first land plants as well as the rise of the great coal forests. The end of the Palaeozoic witnessed the expansion of primitive reptiles, and the end of Cretaceous saw breaking of land due to land mass drifting and climatic warming.
With continuous climatic changes and land mass shifting results, and with the disappearance of many plants and animal species, simultaneously some new species start appearing during environmental selection.
A detailed scheme for ‘Geological time scale’ is given in Table 3.1:
The preceding cursory review of past changes on the Earth thus serves to emphasize the fact that plants and animals have evolved through the times. As environmental conditions slowly changed, flora and fauna responded—either adjusting to a new set of conditions or perishing. To survive as a species, organisms must adapt to the changing environment. This is the case of natural selection.
Essay # 5. Changing Environmental Conditions Associated with Glaciations of Biosphere:
Geological evidence suggests that as many as four major glacial periods occurred in the late Proterozoic (~ 1000 – 540 Ma), the final one, the Varanger ice age, taking place between approximately 610 and 590 Ma.
During the Varanger ice age, more acritarch extinctions occurred than originations, resulting in a decline in overall species number (75% reduction). Following the ice age, there was a large increase in species number and many new and highly ornamented acritarchs appeared.
A tentative link has therefore been suggested between the acritarchs and environmental/oceanographic changes (e.g. changing patterns of marine sedimentation) that accompanied the end of the Varanger glaciation.
Although just two examples are provided above, there are many other suggestions in the literature of bursts of evolutionary activity occurring at or around the same time as significance geological events in this early period of Earth history.
However, it is also highly probable that in these early environments there would have been spiralling ecological relationships. Without a doubt, these would also have had a major impact on species diversity and number, resulting in the development of a complex marine ecosystem of plants and animals by the beginning of the Cambrian period, 590 Ma.
Natural selection results when environmental forces —both abiotic and biotic—favour certain genotypes, as expressed by phenotypes, over others. It functions through non-random reproduction within a population.
Not every individual in a population is able to contribute its share of genetic characteristics to the next generation or leave surviving offspring. Some fail to survive to reproduce, others fail to mate or produce offspring. Their contribution to the gene pool or fitness increases at the expense of others.
On the whole, natural selection tends to eliminate the less fit alleles and favour the most fit. If it favours those close to the population mean, selection is stabilizing and produces little change in the population. It is characteristic of more or less stable environments.
If it favours the extremes, it is disruptive or diversifying. Such selection may occur when segments of a population are subjected to different selection pressures environmentally induced. Or selection may favour one extreme, that is, the population mean in that direction. Characteristic of a changing environment, directional selection produces the most rapid phenotypic and genotypic changes.
Although natural selection may seem to imply a steady improvement or perfection of a species through the times, but that is not the case. Selection pressure may only enable individuals to maintain then fitness over time. Fitness is a response to current environmental conditions and not to some future condition.
Individuals with the greatest fitness in some future situation happen to have the genetic variability that enables them to survive in a changed environment. Nor does natural selection work for the long-term good of the species. While it may improve fitness over the short-term, natural selection may actually work against the long-term survival of a species, especially in situations where natural selection favours speciation.
The great diversity of plants and animals in the world causes one to wonder how all these species arose. Each is adapted to an ecological niche in the ecosystem to which it belongs, and each is genetically independent.
The process by which this has come about, by which one form becomes genetically isolated from the others, is ‘speciation’—the multiplication of species. Speciation is accomplished in most plants and animals by an interaction of heritable variation, natural selection, and barriers to gene flow.
Of major importance to natural selection and adaptation are genetic or inherited variations within a population—the variations that arise from mutations and especially from the shuffling of genes and chromosomes in sexual reproduction.
Variations found in a population are transmitted to the next generation through sexual reproduction when a sample of the gene pool contained in gamete joins to form zygotes.
The most widely accepted mechanism of speciation involves geographic isolation of one part of a population from another. Each part experiences different selection pressures. The two populations diverge and may ultimately become two distinct species. If geographic barriers break down, the two populations may hybridize, or they may evolve strong, usually premating, isolating mechanisms that reinforce their apartness.
That is known as ‘allopatric species’. Another type of speciation mechanism among populations of organisms that have low vagility and inhabit contiguous, that is, different and spatially separated habitats, is ‘parapatric speciation’. It is probably most common among plants.
In parapatric speciation both reproductive isolation and speciation take place within differentiation and the process takes place within a population. The outcome is ‘sympatric speciations’.
How rapidly evolution and speciation take place is, of course, a matter of debate. Sometimes heritable variation takes place within a shortest possible time while in other situation, some species apparently have never changed for millions of years. On the whole evolution among some populations is always taking place somewhere on Earth, even though evolution may not be a continuous process among all populations.
Essay # 6. Diversification of the Biosphere:
Where does individual variation come from? This question is crucial because without the initial variation in the population, natural selection would have nothing to act on. This question troubled Darwin himself because he was not aware of the work of Gregor Mendel who is credited with discovering the laws of inherited variation in 1865.
Indeed, initially Mendel’s work was overlooked, and scientists only rediscovered it in the early 1900s. Mendel discovered that genes, which are the basic units of heredity, pass on traits.
According to the Human Genome Project, humans have an estimated 30,000 to 40,000 genes that determine our traits. Variation in a population, or gene pool, occurs because individuals possess different sets of genes that produce different traits.
How do different sets of genes arise? Reproduction is one way. Genes are shuffled when sperm and egg cells are fused, causing offspring from the same parents to have different genes.
A second cause of genetic variation is mutation, which is a spontaneous change in a gene. Genes are composed of DNA molecules and mutations occur when DNA molecules are altered, such as during DNA replication. Mutation is the ultimate source of all genetic variation.
Evolution through natural selection has produced an increasingly diverse biosphere, with the total number of species becoming greater through time. Initially, evolution was relatively slow. The right side of Fig. 3.2 summarizes the evolution of the life on Earth.