Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

In the context of the nitrogen cycle, what is the role of bacteria?

1. Compose plant matter

2. Breakdown nitrogen for plant use

3. Consume animal waste

4. Fix carbon from the atmosphere

The correct answer is: Breakdown nitrogen for plant use

In the nitrogen cycle, bacteria play a crucial role in transforming nitrogen into forms that plants can utilize. One of the key processes is nitrogen fixation, where specific bacteria convert atmospheric nitrogen (N₂), which plants cannot directly use, into ammonia (NH₃) or related compounds. These conversions are vital because nitrogen is an essential nutrient for plant growth and development, being a fundamental component of amino acids and nucleic acids. The process of breakdown for plant use involves not only nitrogen fixation but also nitrification, where ammonia is further processed by nitrifying bacteria into nitrites (NO₂⁻) and then nitrates (NO₃⁻). Nitrates are the form of nitrogen that plants primarily absorb and utilize for synthesis and growth. Therefore, the understanding of the role of bacteria is essential in appreciating how nitrogen availability in the soil is enhanced through natural biological processes, ultimately sustaining ecosystems and agricultural productivity.