How does nitrogen become protein?

Nitrogen becomes protein through a process called nitrogen fixation, where nitrogen gas from the atmosphere is converted into ammonia by bacteria in the soil or in plant roots. This ammonia can then be incorporated into amino acids, the building blocks of proteins, through various biochemical pathways. Plants absorb these amino acids, and when animals consume the plants, they use the amino acids to synthesize their own proteins, thus integrating nitrogen into their biological systems.