Microbes like Rhizobium, Nitrosomonas and Nitrobacter are used for:
- AOption (a)
nitrogen cycling
- BOption (b)
carbon cycling
- COption (c)
water cycling
- DOption (d)
sulphur cycling
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Correct answer
nitrogen cycling
Why this answer is correct
The correct answer is nitrogen cycling.
Key Points
- Nitrogen Cycle-
- Nitrogen is an essential constituent of protein and is a basic building block of all living tissue. It constitutes nearly 16% by weight of all the proteins that is, converted to ammonia, nitrites or nitrates before it can be taken up by plants.
- Nitrogen fixation on earth is accomplished in three different ways:
a) By microorganisms (bacteria and blue-green algae)
b) By man using industrial processes (fertilizer factories) and
c) To a limited extent by atmospheric phenomena such as thunder and lighting
- Certain microorganisms are capable of fixing atmospheric nitrogen into ammonium ions. These include free-living nitrifying bacteria (e.g. aerobic Azotobacter and anaerobic Clostridium) and symbiotic nitrifying bacteria living in association with leguminous plants and symbiotic bacteria living in non-leguminous root nodule plants (e.g. Rhizobium) as well as blue-green algae (e.g. Anabaena, Spirulina).
- Ammonium ions can be directly taken up as a source of nitrogen by some plants, or are oxidized to nitrites or nitrates by two groups of specialised bacteria: Nitrosomonas bacteria promote the transformation of ammonia into nitrite. Nitrite is then further transformed into nitrate by the bacteria Nitrobacter.
- The nitrates synthesised by bacteria in the soil are taken up by plants and converted into amino acids, which are the building blocks of proteins. These then go through higher trophic levels of the ecosystem. During excretion and upon the death of all organisms nitrogen is returned to the soil in the form of ammonia.
- Certain quantities of soil nitrates, being highly soluble in water, are lost to the system by being transported away by surface run-off or groundwater. In the soil as well as oceans there are special denitrifying bacteria (e.g. Pseudomonas), which convert the nitrates/nitrites to elemental nitrogen. This nitrogen escapes into the atmosphere, thus completing the cycle.
- The periodic thunderstorms convert the gaseous nitrogen in the atmosphere to ammonia and nitrates which eventually reach the earth’s surface through precipitation and then into the soil to be utilized by plants.
Additional Information
- Carbon Cycle
- The carbon cycle involves several processes, including photosynthesis, respiration, decomposition, and combustion. Plants absorb carbon dioxide (CO₂) during photosynthesis, while animals release CO₂ through respiration.
- Carbon is stored in various reservoirs, including the atmosphere (as CO₂), oceans (as dissolved CO₂ and organic carbon), soil (as organic matter), and living organisms. These reservoirs play a crucial role in regulating global climate.
- Human activities, such as fossil fuel combustion and deforestation, significantly alter the carbon cycle by increasing atmospheric CO₂ levels, contributing to global warming and climate change.
- Water Cycle-
- The hydrologic cycle is the continuous circulation of water in the Earth-atmosphere system which is driven by solar energy. Water on our planet is stored in major reservoirs like atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields, and groundwater. Water moves from one reservoir to another by the processes of evaporation, transpiration, condensation, precipitation, deposition, runoff, infiltration, and groundwater flow.
- Water as an important ecological factor determines the structure and function of the ecosystem. Cycling of all other nutrients is also dependent upon water as it provides their transportation during the various steps. It acts as a solvent medium for their uptake of nutrients by organisms.
- Sulphur Cycle-
- The sulphur reservoir is in the soil and sediments where it is locked in organic (coal, oil and peat) and inorganic deposits (pyrite rock and sulphur rock) in the form of sulphates, sulphides and organic sulphur.
- It is released by weathering of rocks, erosional runoff and decomposition of organic matter and is carried to terrestrial and aquatic ecosystems in a salt solution.
- The sulphur cycle is mostly sedimentary except two of its compounds hydrogen sulphide (H2S) and sulphur dioxide (SO2) add a gaseous component to its normal sedimentary cycle.
- Sulphur enters the atmosphere from several sources like volcanic eruptions, combustion of fossil fuels, from the surface of the ocean and from gases released by decomposition. Atmospheric hydrogen sulphide also gets oxidised into sulphur dioxide.
- Atmospheric sulphur dioxide is carried back to the earth after being dissolved in rainwater as weak sulphuric acid.