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Online assignment 1

  4. 4. INTRODUCTION The term “biosphere’’ was first used by the Austrian geologist Edward Suess in 1875.It has been defined by Hutchinson {1970} as that part of the earth in which life exists, ie the envelope of the life. Thus the largest biological system in which several ecosystems can operate together is known as biosphere or ecosphere. The three subdivisions of the biosphere includes: hydrosphere, lithosphere and atmosphere.
  5. 5. 1. Hydrosphere: It means the water envelope i.e.; all the water {liquid} components of the oceans, lakes, rivers and other inland waters. Thus hydrosphere includes two major biocycles, the freshwater and marine. 2. Lithosphere: It includes the solid components of the earth crust ie; rocks, soil and minerals of the continents.[The soil component of the lithosphere has been called pedosphere by Odom]. 3. Atmosphere: It is the gaseous mantle which envelope the hydrosphere and the lithosphere. Although the air is traversed by many kinds of animals and plant propagules there are no permanent inhabitants.
  7. 7. Living organisms require energy. This energy comes from the sun. Only a small quantity of total energy received from the sun is utilized by the living organisms for their energy need. Living organisms also require organic inorganic materials from each of these subdivisions of the biosphere. The hydrosphere supplies water; the lithosphere provides all necessary minerals; and the atmosphere supplies oxygen, nitrogen, carbon dioxide. These inorganic materials provide all the chemical elements needed in the building and maintenance of living organic matter. In addition all the three subdivisions of the biosphere also influence metabolic activities of the living organisms in various other specific ways. As far as energy is concerned, the earth is an open system. It receives energy perennially from the sun. With regard to materials the earth and its atmosphere are practically a closed system. ENERGY FLOW One important aspect of ecosystem is the production of chemical energy and its utilization. All organisms in an ecosystem require energy for their life activities. The energy requirement is met from the solar energy is actually trapped for the functioning of ecosystem. The radiant energy of the sun is trapped by green plants (producers) and converted into chemical energy of the organic molecules. Green plants do this by a process of photosynthesis producing carbohydrate from CO2 and H2O. This trapping of light energy and its conversion into chemical energy is called energy fixation. Some of the organic molecules are used by plants to produce energy for their cellular activities; but the major portion of the organic molecules is stored up in the form of starch, protein and far.
  8. 8. From the producers the energy flows into the primary, secondary and tertiary consumers and decomposers. A portion of the energy is lost from organisms into the environment during their respiratory activities. So the amount of energy transferred to the next higher level gradually decreases. Finally with the decomposition of organisms the entire energy disappears or becomes lost into the environment in the form of heat. Eventually all the solar energy that entered the living system through the producers goes back into the non-living world not as light but as heat. Hence there is no cycling of energy in an ecosystem through the producers goes back into the non-living world not as light but as heat. Hence there is no cycling of energy in an ecosystem though materials can be recycled. The continuous trapping of light energy by green plants makes good this and maintains an uninterrupted flow of energy in an ecosystem. Energy is essential for circulation of matter (organic and inorganic) and continuance of life. The ultimate source of energy for the ecosystem is the sun. Sun radiates energy in the form of light, infrared and ultraviolet rays. Almost half of the solar energy constitutes light. Only light wave is visible to us and tts gives us light. The infrared rays provide us with the heat energy. The atmosphere filters most of the sun’s radiations as it reaches earth thus shiclding the earth from its harmful effects. Most of the infrared rays are absorbed by the atmosphere and is
  9. 9. radiated back thus regulating the earth’s temperature. The ozone layer of the atmosphere absorbs the ultraviolet rays. Thus most part of the energy reaches the earth in the form of light and heat which regulate the climate phenomena. Only one percent of the solar energy is trapped by the green plants during photosynthesis get incorporated into organic compounds. The rate at which organic molecules are formed in photosynthesis (green plants) is called gross primary productivity. This is also known as total photosynthesis or total assimilation. Some part of these compounds is used in the catabolic processes of plants and the rest is stored in the body in the form of biomass. Any such storage of energy is called net primary productivity. It is thus the rate of storage of organic matter in plant tissues in excess of the respiratory utilization by the plants during the measurement period. This is also known as “apparent photosynthesis” or net assimilation. The term community productivity refers to the berate at which organic substances are formed in all the autotrophs in a community. Energy that incorporated by the producers is transported through the different tropic levels in the form of food. At each level as explained earlier some amount is used up in catabolic processes and a part is stored as biomass. The rate of energy storage at consumer levels (heterotrophs) is called secondary productivity. When plants are eaten by herbivorous about 10 percent of the energy in the food is fixed into animal flesh. And when a carnivore eats a herbivore only about 10 percent of the energy is fixed. Therefore the secondary consumer gain in energy is only 0.01 percent of the net productivity of plants. ENERGY PATHWAY In every ecosystem basically two types of food chains are recognized grazing food chain and detritus food chain. The grazing food chain starts from green plants and ends to carnivorous by passing through herbivorous. Thus gross production of a plant in an ecosystem many mate three fates it may be oxidized in respiration, it may die and decay and it may be eaten by plant eating plants or herbivorous. In herbivores the
  10. 10. assimilated food can be stored as carbohydrates, proteins or fats, transformed into relatively simple substances or rebuilt by the animal into much more complex organic molecules. The energy to perform these transformations is supplied by respiration. Like autotrophs, the ultimate deposition of energy in herbivores occurs by three routes; respiration, decay or organic matter by bacteria and other decomposer organisms and consumption by carnivores. The organic wastes exudates and dead matter derived from the grazing food chain are generally known as detritus. The energy contained in this detritus is not lost to the ecosystem as a whole. It serves as the source of energy for a group of organisms (detritivores) that are separate from the grazing food chain and it represents a very important component in the energy flow of an ecosystem. Thus there are two energy pathways in every ecosystem. In fact in some ecosystems (grassland, forest) more energy flows through the detritus food chain than through the grazing food chain. In the marine community the energy flow via the grazing food chain is more than via the detritus path way. In the detritus food chain the energy flow remains as a continues passage. In grazing food chain it is a step wise flow between separate entities. Further, in the grazing food chain the energy storage is entirely within the tissues of living organisms whereas energy storage for the detritus food chain may be external to the organisms and is the detritus itself. “All life comes from the sun. Any measure of the sun’s effect should be correlated with biological productivity.” F.C.W.Olson-1956 When the prophet Isaiah proclaimed (40.6,7) “…all flesh is grass…” presumably his primary intent was to emphasize the transistorizes of the bodily condition. However, the aphorism embodies the basic premise of all ecological studies on living communities: the ultimate source of all animal and human food is “grass” or the true green plants, which alone can transform or transducer solar energy unavailable to animals to a form available to the latter. BIOGEOCHEMICAL CYCLES OR CYCLES OF MATTER. The chemical elements tend to circulate in the biosphere in characteristic paths from environment to organisms
  11. 11. and back to the environment. These more or less circular paths are known as biogeochemical (bio-life; geo-earth) or cycles of matter. There are two basic types’ biogeochemical cycles. 1. Gaseous cycles: The reservoir of the materials is the atmosphere or hydrosphere. Carbon, Oxygen, and nitrogen cycles are examples. 2. Sedimentary cycles: The reservoir is the lithosphere; phosphorous, sulphur and calcium cycles are examples. The hydrologic (water) cycle has been included in gaseous cycles by Odom. But Kormondy (1969) considers it to be a separate cycle, involving the movement of a compound, while the others involve the movement of elements. The movement of those elements and inorganic compounds that are essential to life can referred to as nutrient cycling. THE OXYGEN CYCLE. The atmosphere oxygen enters the living world as a gas required in respiration. During this process carbon dioxide and water are formed.
  12. 12. C6H12O6 + 602=6CO2+6H2O+Energy. The metabolic water thus formed may undergo one of the following fates. i) Some of it may be excreted and added to the environment. ii) Another part may be used as a building material of protoplasm and remains their until death. iii) Some of the water is also utilized as raw material in photosynthesis by green plants. 6CO2+6H2O+ LIGHT ENERGY=C6H2O6+6O2 Such free oxygen may know again be used in respiration or it may be returned to the environment as atmospheric oxygen, completing the cycle. CARBON CYCLE Atmospheric carbon dioxide is the main carbon source which is produced mainly through respiration. The gas enters living system through photosynthesis and gets incorporated in organic compounds, protoplasm, etc. (plants and animals). Death and decay, subsequently returns CO2 to the atmosphere and thus completes one
  13. 13. possible carbon cycle. Another fraction of the organic substances is used as fuel in respiration by both plants and animals. This process releases CO2 by a product. Such carbon dioxide may now be used in photosynthesis or it may return to the environment, completing the second possible carbon cycle. Forest fires and burning of industrial fuel release CO2 into the air. Volcanic eruptions also add CO2 to the atmosphere. NITROGEN CYCLE 79 percent of the atmosphere is Nitrogen. It is required by organisms in the synthesis of proteins, nucleic acids and other nitrogenous compounds. Aerial nitrogen is not utilized as such by the organisms but nitrite and nitrate ions are absorbed from the environment which may be converted into nitrogenous components of the living matter. Plants obtain nitrogen mostly in the form of nitrates.
  14. 14. When a plant or animal dies the nitrogenous body is decomposed by microbes producing ammonia. This process is called ammonification. Ammonia is washed into the soil where ammonium compounds are formed. Some green plants can take ammonium ions directly into their roots. Some nitrifying bacteria in the soil (nitrosomonas and nitrobacteria) oxidize the ammonium compounds into nitrites (NO2) and finally to nitrates (NO3).This process is called nitrification. These are absorbed by the plants from soil solution. (Thus the saprophytic bacteria play a role of scavengers in nature. There can be regarded as the symbiotic nitrogen fixing bacteria). Symbiotically some bacteria (Rhizobium) fix nitrogen into the roots of leguminous plants. Both these types make the soil fertile. Other types of bacteria (Pseudomonas) break down nitrogen compounds are liberated into the atmosphere. This is denitrification. Hence the fertility of the soil is lost. PHOSPHOROUS CYCLE As a basic constituent of nucleic acids, phospholipids and numerous phosphorylated compounds, phosphorous is one of the nutrients of major importance to biological systems. The great reservoirs of phosphorous are the rocks or other deposits which have been formed in past geological ages.
  15. 15. These are gradually eroding, releasing phosphates to ecosystems. But much phosphates escapes into the sea where part of it deposited in the shallow sediments and part of it is lost to the deep sediments. For their nutrition plants require inorganic phosphates dissolved in water. This phosphate is transferred to animal consumers and decomposers as organic phosphate and subsequently is made available for recycling via mineralizing decomposition. Much phosphate becomes lost to this central cycle as sediments. Formation of teeth and bone also account for considerable losses from the major portion of cycle. The fish and marine birds have played apparently an important role in returning phosphorous to the cycle. SULPHUR CYCLE Sulphur is an essential part of protein and amino acids and is characteristic of organic compounds. Inorganic sulphate (SO4) is the major source of biologically significant sulphur. Plants absorb sulphates from the soil and use sulphur in protein synthesis. Through food this organic sulphur is transferred to animal bodies. Most of the biologically incorporated sulphur (in plant and animal bodies) is mineralized as sulphate by bacteria and fungi in ordinary decomposition under aerobic condition. Under anaerobic condition however some may be reduced directly to sulphides (SO4=H2S). The sulphides produced are harmful to most organisms but certain bacteria oxidize sulphides into sulphates (H2S=SO4). Some organic sulphur enters the atmosphere as sulphur dioxide through incomplete
  16. 16. combustion of fossil fuels, especially coal. This is one of the major sources of air pollution today. Atmospheric sulphur dioxide, soluble in water is carried back to earth in rain water. Sulphur in soluble form mostly as sulphate is absorbed through plant roots. Sulphur cycle is a good example to illustrate linkage between air, water and soil, i.e., sulphur cycle includes both gaseous phase and sedimentary phase. CALCIUM CYCLE Calcium is also cycled like other materials. Calcium is slowly released from the rocks by water and wind actions. It is then absorbed by plants through their roots. Recycling occurs between living organisms and their environment. Corals and Molluscs deposit a large quantity of calcium in their skeleton and shells. These materials are not available for immediate cycling. In sedimentary cycles, some portion of the exchangeable material tend to get ‘lost’ for long period, as in deep ocean deposits, and thereby becomes in accessible to organisms and to continual cycling. It is returned to the cycle through sea food chain-fish and birds. ECOLOGICAL IMBALANCE AND ITS CONSEQUENCES
  17. 17. Early man was in every way adapted to his biosphere. There were plenty of natural resources, and therefore there was no competition for them. In other words, the world of man and the world of nature were in perfect balance. With the advent of agriculture and technological revolution a new relationship arose. Now man occupies a unique position in the biosphere. Man being a dominant organism of most ecosystems, controls and modifies environment more extensively than any other organism. In fact, there have been significant changes in the natural environments due to man’s intervention and his rapid progress in colonization, urbanization, industrialization, agriculture, mining, transportation, and technology. With these changes the biosphere became transformed into a human dominated environment or atmosphere. The discriminated exploitation of nature and natural resources has become detrimental to ecological balance. Despite men’s awareness to his ecological resources exist for his own benefit. Their exploitation without proper malpractices, still in many tropical lands deforestation is occurring at increasing rates. In India, deforestation, overgrazing and hydroelectric power development schemes are invading the new national parks and forest reserves. Much of this environment destruction is done in the name of economic development.
  18. 18. Man’s general view is that earth’s conservation has been very disastrous. Unplanned development breaks ecological as well as human laws. Unfortunately such human activities resulted into what we commonly call the ecological backlashes or ecological boomerangs, which may be defined as ‘’ an unforeseen detrimental consequence of an environmental modification with cancels cut the projected gain or, as it too often the case, actually creates more problems than it solves’’ (Odum). Farvar and Milton (1969) and Cahn (1968) describe a number of severe ecological backlashes on the international level. For example, building of huge dams in undeveloped tropical countries (dam on the Zambezi River in Africa) has created a series of “unforeseen” problems such as decline in fish catch and soil erosion. The large lake shore increased the habitat for tsetse flies with a resultant outbreak in cattle disease (also in human disease in the case of dams on the Nile). An important factor that has created more environmental problems is the explosion of explosion of human population. Human activities have modified many natural biotic communities. Deforestation has resulted in the extinction of several species. Some of the changes in the landscape have altered the regional climate. Man has replaced diverse stable ecosystems by simple, vulnerable man- made ecosystems. Use of chemical fertilizers have altered the soil condition in many areas and transformed fertile land to waste lands. Construction of canals for irrigations has caused many imbalances. Even tampering with the animal communities has created fresh problems. For instance, the Indian mongoose which has introduced into the West Indies in the hope controlling rats found to be ineffective. Instead it turned out to be a predator of harmful birds and reptiles. CONCLUSION Due to man’s numerical ecological malpractices’ and short sighted and greedy exploitation of different ecological resources such as air, water, minerals, vegetation, etc. human civilization has to face many serious ecological problems such as energy crisis, pollution, flood, erosion, pesticide contamination, radio isotope accumulation, population growth, depletion of vital natural resources, infectious diseases ,etc.,. If some ecologically sound measures are not applied to human utilization of his environment, there may arise several uncontrollable ecological hazards which may become responsible for the extermination, extinction and devastation of human race from the biosphere.