Final answer:
Nitrogen in organisms comes from the environment predominantly through nitrogen-fixing bacteria that convert atmospheric nitrogen into forms plants can absorb. Animals obtain nitrogen by consuming plants or other animals, integrating nitrogen from the environment into their bodies. This is part of the nitrogen cycle, which recycles nitrogen throughout ecosystems.
Step-by-step explanation:
Understanding the Nitrogen Cycle and the Origin of Nitrogen in Organisms
All organisms, including humans, require nitrogen to synthesize essential biological molecules such as proteins and nucleic acids. Although nitrogen is abundant in the atmosphere as nitrogen gas (N₂), it must undergo a process called nitrogen fixation to be converted into a form that organisms can utilize. Nitrogen-fixing bacteria, often found in soil or in symbiotic relationships with plant roots, are capable of converting atmospheric nitrogen into ammonia (NH₃), subsequently used by plants to form amino acids and other nitrogenous compounds. Through consumption of plant material or organisms that have fed on plants, animals, including humans, obtain their nitrogen. This signifies that the nitrogen within our bodies has primarily originated from other living organisms and the processes occurring in the environment.
The recycled nature of nitrogen in ecosystems, known as the nitrogen cycle, involves several steps. After nitrogen fixation, nitrogen compounds are further processed into nitrites (NO₂) and nitrates (NO₃) which plants absorb. These plants then become a source of organic nitrogen for consumers in the food web. Following consumption, the nitrogenous wastes are processed back by soil bacteria into gaseous nitrogen. This constant cycling allows for nitrogen from the environment and other organisms to become part of our own organic makeup.