Lec-3
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Biogeochemical cycle Nearly 30 to 40 elements are required for proper growth and development of living organisms. Most important of these are C, H, O, P, Cl, Zn etc. These materials flow from abiotic to biotic components and back to the non-living component again in a more or less cyclic manner. This is known as the biogeochemical cycle or inorganic-organic cycle. There are three types of biogeochemical cycles: 4. Hydrologic cycle or water cycle 5. Gaseous cycles and 6. Sedimentary cycles
1. Hydrologic or water cycle Interchange of water between atmosphere, land and sea also between living organisms and their environment is accomplished through water cycle. Water cycle or hydrologic cycle involves evaporation, transpiration, cloud formation and precipitation. Water of atmosphere reaches the earth surface through precipitation and from the earth surface it reaches the atmosphere through evaporation and transpiration.
The amount of water available for evaporation is determined by the amount supplied by the precipitation and condensation. Between rainfall input and evaporation output there lies a precarious water balance.
Gaseous Cycles A.Oxygen cycle: Oxygen is found in free state in atmosphere and dissolved state in water. Organisms liberate carbon dioxide by their respiration process which is utilized by green plants as an essential raw material for carbohydrate synthesis as well as for photosynthesis . Oxygen is liberated as byproduct of photosynthesis by the producer. In this way, a simple yet vital oxygen cycle is maintained in the ecosystem.
Figure 9l-1: Inputs and outputs of the photosynthetic process.
B. Carbon cycle: Carbon is the basic constituent of all organic compounds. Carbon dioxide which is found in free state in atmosphere and in dissolved state in the water on the earth. Green plants use carbon dioxide through photosynthesis in the presence of sunlight and carbohydrate is formed. Later on complex fats and polysaccharides are formed in plants which are utilized by animals. .
Flesh eating animals feed on herbivores and the carbon compounds are again digested and converted into the other form. Carbon is released to the atmosphere directly as carbon dioxide in respiration of both plants and animals. Bacteria and fungi attack the dead remains of plants and animals. They degrade the complex organic compounds in to simple substances which are then available for other cycles. Part of the organic carbon becomes incorporated into the earth’s crust as coal, gas, petroleum, limestone and coral reef. Carbon from such deposits may be liberated after a long period of time
carbon cycle
C. Nitrogen cycle: All life requires nitrogen-compounds, e.g., proteins and nucleic acids. Air, which is 79% nitrogen gas (N2), is the major reservoir of nitrogen. The atmospheric nitrogen is not directly available to the organisms with the exception of some prokaryotes like blue green algae and nitrogen fixing bacteria.
Nitrogen cycle Nitrogen cycle consists of the following steps: 2. Nitrogen fixation 3. Nitrogen assimilation 4. Ammonifiation 5. Nitrification 6. Denitrification
Nitrogen fixation: Conversion of free nitrogen of atmosphere into the biologically acceptable from or nitrogenous compounds is referred to as nitrogen fixation. This process is of two types:
a. Physicochemical or non-biological nitrogen fixation: In this case , atmospheric nitrogen combines with oxygen during lightning or electrical discharge in the cloud and produce different nitrogen oxides; The nitrogen oxides get dissolved in rain water and on reaching earth surface they react with mineral compounds to form nitrates and other nitrogenous compounds.
b) Biological nitrogen fixation: It is carried out by certain prokaryotes some blue-green algae. They fix significant amounts of nitrogen in the oceans, lake and soils. Symbiotic bacteria (Rhizobium, a blue-green algae) inhabiting the root nodules of legumes fix atmospheric nitrogen. Certain free living nitrogen fixing bacteria also fix free nitrogen of atmosphere in the soil.
2. Nitrogen assimilation: Inorganic nitrogen in the form of nitrates (NO3), nitrites (NO2) and ammonia (NH4) is absorbed by the green plants and converted in to nitrogenous organic compounds. Nitrates are first converted in to ammonia which combines with organic acids to form amino acids. Amino acids are used in the synthesis of proteins, enzymes chlorophylls, nucleic acids etc. Animals derive their nitrogen requirement from the plant proteins.
Nitrogen assimilation NO3
( NH4 + organic acids) = amino acid uses for production of
Conversion
Animals Consumption
proteins, enzymes chlorophylls, nucleic acids etc.
3. Ammonification:
The dead organic remains of plants and animals and excreta of animals are acted upon by a number of microorganisms especially actinomycetes and bacilli. These organisms utilize organic compounds in their metabolism and release ammonia.
4. Nitrification: Certain bacteria , such as Nitrosomonas, Nitrococcus in oceans and soils convert ammonia into nitrites and then nitrites in to nitrates. These bacteria primarily use the energy of dead organic matter in their metabolism. Conversion of nitrites to nitrates in brought about by several microbes like penicillium species, Nitrobnacter etc. NH4
NO2
NO3
Nitrification 5. Denitrification: Ammonia and nitrates are converted in to free nitrogen by certain microbes. This process is referred to as denitrifleation. Micrococcus is the common examples of denitrifying bacteria. NH4 / NO3
N2
3. Sedimentation cycle Nitrates of the soil are washed down to the sea or leached deep into the earth along with percolation water. Nitrates thus lost from the soil surface are locked up in the rocks. This is sedimentation of nitrogen. Nitrogen of rock is released only when the rocks are exposed and weathered. Other elements of this environment are also regulating through sedimentation cycle.
Sedimentation cycle Phosphorus (P) cycle- Plants and animals obtains phosphorus from the environment. Phosphorus is a component of nucleic acids, ATP, NADP etc. It occurs in the soil as rock phosphate. Phosphorous occurs in the soil in five form: P1, P2, P3, P4, P5. The dissolved phosphorous is absorbed by plants and converted to organic form. From plants is travels to various trophic levels in the form of organic phosphates. When the plants and animals die the decomposers attack them and liberate phosphorous to the environment. Thus this process proceeds in cyclic way.
Phosphorous along with many other mineral elements reaches the oceans and settles down as sediment. A good proportion of P leaches down to deep layers of soil. In this way, major proportion of P becomes lost to this cycle by physical processes, such as sedimentation and leaching. Biological processes such as formation of teeth and bones also keep P locked up for some time.
1. Hydrologic or water cycle Interchange of water between atmosphere, land and sea also between living organisms and their environment is accomplished through water cycle. Water cycle or hydrologic cycle involves evaporation, transpiration, cloud formation and precipitation. Water of atmosphere reaches the earth surface through precipitation and from the earth surface it reaches the atmosphere through evaporation and transpiration.
The amount of water available for evaporation is determined by the amount supplied by the precipitation and condensation. Between rainfall input and evaporation output there lies a precarious water balance.
Gaseous Cycles A.Oxygen cycle: Oxygen is found in free state in atmosphere and dissolved state in water. Organisms liberate carbon dioxide by their respiration process which is utilized by green plants as an essential raw material for carbohydrate synthesis as well as for photosynthesis . Oxygen is liberated as byproduct of photosynthesis by the producer. In this way, a simple yet vital oxygen cycle is maintained in the ecosystem.
Figure 9l-1: Inputs and outputs of the photosynthetic process.
B. Carbon cycle: Carbon is the basic constituent of all organic compounds. Carbon dioxide which is found in free state in atmosphere and in dissolved state in the water on the earth. Green plants use carbon dioxide through photosynthesis in the presence of sunlight and carbohydrate is formed. Later on complex fats and polysaccharides are formed in plants which are utilized by animals. .
Flesh eating animals feed on herbivores and the carbon compounds are again digested and converted into the other form. Carbon is released to the atmosphere directly as carbon dioxide in respiration of both plants and animals. Bacteria and fungi attack the dead remains of plants and animals. They degrade the complex organic compounds in to simple substances which are then available for other cycles. Part of the organic carbon becomes incorporated into the earth’s crust as coal, gas, petroleum, limestone and coral reef. Carbon from such deposits may be liberated after a long period of time
carbon cycle
C. Nitrogen cycle: All life requires nitrogen-compounds, e.g., proteins and nucleic acids. Air, which is 79% nitrogen gas (N2), is the major reservoir of nitrogen. The atmospheric nitrogen is not directly available to the organisms with the exception of some prokaryotes like blue green algae and nitrogen fixing bacteria.
Nitrogen cycle Nitrogen cycle consists of the following steps: 2. Nitrogen fixation 3. Nitrogen assimilation 4. Ammonifiation 5. Nitrification 6. Denitrification
Nitrogen fixation: Conversion of free nitrogen of atmosphere into the biologically acceptable from or nitrogenous compounds is referred to as nitrogen fixation. This process is of two types:
a. Physicochemical or non-biological nitrogen fixation: In this case , atmospheric nitrogen combines with oxygen during lightning or electrical discharge in the cloud and produce different nitrogen oxides; The nitrogen oxides get dissolved in rain water and on reaching earth surface they react with mineral compounds to form nitrates and other nitrogenous compounds.
b) Biological nitrogen fixation: It is carried out by certain prokaryotes some blue-green algae. They fix significant amounts of nitrogen in the oceans, lake and soils. Symbiotic bacteria (Rhizobium, a blue-green algae) inhabiting the root nodules of legumes fix atmospheric nitrogen. Certain free living nitrogen fixing bacteria also fix free nitrogen of atmosphere in the soil.
2. Nitrogen assimilation: Inorganic nitrogen in the form of nitrates (NO3), nitrites (NO2) and ammonia (NH4) is absorbed by the green plants and converted in to nitrogenous organic compounds. Nitrates are first converted in to ammonia which combines with organic acids to form amino acids. Amino acids are used in the synthesis of proteins, enzymes chlorophylls, nucleic acids etc. Animals derive their nitrogen requirement from the plant proteins.
Nitrogen assimilation NO3
( NH4 + organic acids) = amino acid uses for production of
Conversion
Animals Consumption
proteins, enzymes chlorophylls, nucleic acids etc.
3. Ammonification:
The dead organic remains of plants and animals and excreta of animals are acted upon by a number of microorganisms especially actinomycetes and bacilli. These organisms utilize organic compounds in their metabolism and release ammonia.
4. Nitrification: Certain bacteria , such as Nitrosomonas, Nitrococcus in oceans and soils convert ammonia into nitrites and then nitrites in to nitrates. These bacteria primarily use the energy of dead organic matter in their metabolism. Conversion of nitrites to nitrates in brought about by several microbes like penicillium species, Nitrobnacter etc. NH4
NO2
NO3
Nitrification 5. Denitrification: Ammonia and nitrates are converted in to free nitrogen by certain microbes. This process is referred to as denitrifleation. Micrococcus is the common examples of denitrifying bacteria. NH4 / NO3
N2
3. Sedimentation cycle Nitrates of the soil are washed down to the sea or leached deep into the earth along with percolation water. Nitrates thus lost from the soil surface are locked up in the rocks. This is sedimentation of nitrogen. Nitrogen of rock is released only when the rocks are exposed and weathered. Other elements of this environment are also regulating through sedimentation cycle.
Sedimentation cycle Phosphorus (P) cycle- Plants and animals obtains phosphorus from the environment. Phosphorus is a component of nucleic acids, ATP, NADP etc. It occurs in the soil as rock phosphate. Phosphorous occurs in the soil in five form: P1, P2, P3, P4, P5. The dissolved phosphorous is absorbed by plants and converted to organic form. From plants is travels to various trophic levels in the form of organic phosphates. When the plants and animals die the decomposers attack them and liberate phosphorous to the environment. Thus this process proceeds in cyclic way.
Phosphorous along with many other mineral elements reaches the oceans and settles down as sediment. A good proportion of P leaches down to deep layers of soil. In this way, major proportion of P becomes lost to this cycle by physical processes, such as sedimentation and leaching. Biological processes such as formation of teeth and bones also keep P locked up for some time.
