The nitrogen cycle refers to the process by which nitrogen is converted into different chemical forms as it circulates through the air, water, and soil. It plays a vital role in plant growth and is an essential component of amino acids, proteins, and nucleic acids that are necessary for life. The nitrogen cycle consists of several stages including nitrification, denitrification, ammonification, and deposition. Nitrogen gas (N2) makes up about 78% of the Earth's atmosphere but is not directly usable by plants. It gets converted into other forms such as nitrate (NO3-) or ammonium (NH4+) through processes like nitrification, which are carried out by bacteria. These compounds can be taken up by plants and incorporated into their tissues. However, when plants and animals die, the nitrogen is returned to the soil through decomposition. Some of this nitrogen gets converted back into atmospheric N2 through a process called denitrification carried out by other bacteria. This cycle continues indefinitely, making nitrogen available for use by living organisms and maintaining ecosystem balance.