Which correctly describes the nitrogen cycle?

The nitrogen cycle is a crucial ecological process that highlights the movement and transformation of nitrogen in different forms through various ecosystems. The correct description emphasizes the role of bacteria in converting nitrogen compounds into forms that plants and animals can utilize.

In this cycle, nitrogen exists in the atmosphere primarily as molecular nitrogen (N₂), which is not directly usable by most living organisms. Certain bacteria, particularly nitrogen-fixing bacteria, have the unique ability to convert this atmospheric nitrogen into ammonia or related compounds. This process is vital as it allows nitrogen to enter the soil in forms that plants can absorb and assimilate. Subsequently, when animals consume these plants, they also obtain nitrogen, which is essential for creating proteins and nucleic acids.

Furthermore, the role of bacteria continues as some specialized bacteria can convert nitrogenous waste products from animals back into forms such as nitrates, which plants can again absorb. This interconnectedness underscores how bacteria play a critical part in maintaining the nitrogen cycle and ensuring that nitrogen is available throughout the ecosystem for various life forms.

The incorrect options do not accurately reflect the complexities and the essential nature of the nitrogen cycle. For instance, saying that nitrogen is only used by animals ignores the foundational role that plants play in acquiring nitrogen through their uptake of nitrates.