7. Explain nitrogen cycle and draw a schematic diagram of nitrogen cycle.

The nitrogen cycle is a biogeochemical process that describes the movement and transformation of nitrogen in various forms within ecosystems. Nitrogen is an essential element for the growth and survival of living organisms, as it is a component of proteins, nucleic acids, and other biomolecules. The nitrogen cycle involves several key processes, including nitrogen fixation, nitrification, denitrification, and ammonification. Here's an overview of the nitrogen cycle:

1. Nitrogen Fixation: Nitrogen fixation is the process by which atmospheric nitrogen gas (N2) is converted into a form that can be utilized by plants and other organisms. This conversion is primarily carried out by nitrogen-fixing bacteria, such as Rhizobium species in the roots of leguminous plants (e.g., peas, beans) and cyanobacteria in soil and aquatic environments. These bacteria possess the enzyme nitrogenase, which allows them to convert N2 gas into ammonia (NH3) or ammonium ions (NH4+), which can be assimilated by plants.

2. Ammonification: Ammonification is the process by which organic nitrogen compounds, such as proteins and nucleic acids from dead plant and animal matter, are broken down into ammonia (NH3) or ammonium ions (NH4+) by decomposer organisms, such as bacteria and fungi. These organisms release ammonia as a byproduct of their metabolic processes, making it available for uptake by plants in the soil.

3. Nitrification: Nitrification is a two-step process in which ammonia (NH3) or ammonium ions (NH4+) are converted into nitrite (NO2-) and then into nitrate (NO3-) by nitrifying bacteria. The first step is carried out by ammonia-oxidizing bacteria, such as Nitrosomonas species, which oxidize ammonia to nitrite. The second step is performed by nitrite-oxidizing bacteria, such as Nitrobacter species, which oxidize nitrite to nitrate. Nitrate is the primary form of nitrogen taken up by plants for growth and is also susceptible to leaching into groundwater.

4. Assimilation: Plants and other organisms assimilate nitrogen from the soil in the form of nitrate (NO3-) or ammonium ions (NH4+) to synthesize proteins, nucleic acids, and other nitrogen-containing compounds essential for growth and development.

5. Denitrification: Denitrification is the process by which nitrate (NO3-) is converted back into atmospheric nitrogen gas (N2) by denitrifying bacteria under anaerobic conditions. These bacteria reduce nitrate to nitrite (NO2-), nitric oxide (NO), nitrous oxide (N2O), and eventually to nitrogen gas (N2), which is released back into the atmosphere. Denitrification helps to balance the nitrogen cycle and prevent the accumulation of excess nitrogen in ecosystems
   Atmospheric N2 (nitrogen gas)   -->  Nitrogen Fixation   -->   Ammonia (NH3) / Ammonium ions (NH4+)
                                                                       |
                                                                       v
                                                                       Ammonification
                                                                       |
                                                                       v
                                                                       Nitrification
                                                                       |
                                                                       v
                                                                       Assimilation
                                                                       |
                                                                       v
                                                                       Denitrification
                                                                       |
                                                                       v
   Atmospheric N2 (nitrogen gas)
   
   

   This diagram illustrates the flow of nitrogen through different forms and processes within the nitrogen cycle, demonstrating the interconnectedness of nitrogen in terrestrial and aquatic ecosystems.