MEGA Elementary Education Multi-Content Practice Test

What role do nitrogen-fixing bacteria play in the nitrogen cycle?

1. Converting atmospheric nitrogen into a form usable by plants

2. Degrading nitrogen compounds present in animal feces

3. Releasing nitrogen from proteins in dead plant material

4. Returning nitrogen gas to the atmosphere

The correct answer is: Converting atmospheric nitrogen into a form usable by plants

Nitrogen-fixing bacteria are essential to the nitrogen cycle primarily because they have the unique ability to convert atmospheric nitrogen (N2) into ammonia (NH3) or related compounds that are biologically available for plants. This process is crucial because atmospheric nitrogen makes up about 78% of the Earth's air but is not usable by most living organisms in its gaseous form. Through nitrogen fixation, bacteria, particularly those found in the root nodules of legumes (like Rhizobium), can assimilate this inert form of nitrogen and help create a nutrient that plants can absorb and utilize for growth. This process not only supports plant life but also sustains the entire food web since plants serve as the primary producers in most ecosystems. In summary, the role of nitrogen-fixing bacteria is foundational for ensuring that nitrogen, a vital nutrient, is accessible to living organisms, promoting healthy soils and ensuring the productivity of agricultural systems.