Final answer:
Nitrogen is crucial for plant growth as it is a fundamental component of proteins and nucleic acids, but must be 'fixed' from atmospheric nitrogen (N₂) into a usable form through a process called Nitrogen Fixation, primarily accomplished by soil bacteria.
Step-by-step explanation:
Nitrogen is important for plant growth. In the atmosphere, Nitrogen exists as N₂, which is unusable by most plants because of its strong triple bond. For plants to utilize nitrogen, it must be 'fixed' into a form they can absorb, such as ammonium (NH4) or nitrate (NO3). This process is called Nitrogen Fixation and is essential because nitrogen is a crucial component of proteins and nucleic acids like DNA. While atmospheric nitrogen is abundant, comprising approximately 78% of Earth's atmosphere, it is mostly inert and must go through the nitrogen cycle to become accessible to living organisms.
Nitrogen fixation is primarily carried out by certain bacteria, some of which form symbiotic relationships with plant roots. These bacteria convert nitrogen gas into ammonia (NH3), which the plants can then use. Through this process, plants gain the nitrogen necessary to synthesize proteins and other vital organic molecules.