How do living organisms obtain their nitrogen requirement?

Answer 1

All organisms need nitrogen to live and grow. Plants take up nitrate ions from the soil, they are then absorbed into roots by active transport, the plant then produces nitrogen-containing compounds such as protein. This nitrogen then gets into the food web as primary consumers feed on plants and obtain the nitrogen-containing compounds. However, the atmosphere is made up of 78% nitrogen and is unavailable in this form to organisms. This is due to the triple bond between the two N atoms causing it to be inert. To be used by organisms, it must be converted to a chemically available form, such as ammonium (NH4+), nitrate (NO3-), or urea ((NH3)2CO). There are five main processes that convert nitrogen to a more accessible form. They are; nitrogen fixation, nitrogen uptake, decay process, nitrification and denitrification. The first process I will talk about is nitrogen fixation. There, the nitrogen is converted to ammonium; it is the only way organisms can obtain nitrogen directly from the atmosphere. The only organism that can fix nitrogen through metabolic process is bacteria from the genus Rhizobium. The nitrogen fixers are usually found on host plants, but there are also nitrogen fixing bacteria found without host plants. They are known as free-living nitrogen fixers, e.g. in the aquatic environment a very important nitrogen fixer would be cyanobacteria. Nitrogen fixation can also be carried out in high-energy natural events, such as lightning and forest fires. The high-energy breaks the triple bond between the two nitrogen atoms producing a significant amount of single nitrogen atoms available for use. The next process is nitrogen uptake, this is where plants or bacteria itself makes use of the ammonia produced by the nitrogen fixing bacteria. The ammonium is converted from NH4+ to N to make protein or other nitrogen containing compounds. A very important process that returns nitrogen back to the nitrogen cycle for use is the decay process. When organisms, die, nitrogen is converted back into inorganic nitrogen by a process called nitrogen mineralization. Decomposers consume the organic matter and this leads to decomposition. Nitrogen contained within the dead organism in converted to ammonium, it is then available for use to plants, or transformed into NO3- (nitrification). Through the nitrogen cycle, food-making organisms obtain necessary nitrogen through nitrogen fixation and nitrification. Nitrogen compounds are returned to atmosphere and soil through decay and denitrification. In crops, few plants are left to decay back into soil, so the nitrogen cycle doesn't supply enough nitrogen to support plant growth. Therefore natural or artificial fertilizers containing NO3- or NH4+ compounds are added.

Answer 2

By eating the part of plants that store the nitrogen in the soil.