National League for Nursing (NLN) Science Practice Exam

Which type of microorganism can convert atmospheric nitrogen into a form usable by plants?

1. Bacteria

2. Fungi

3. Viruses

4. Algae

The correct answer is: Bacteria

The correct choice is bacteria, specifically nitrogen-fixing bacteria. These microorganisms possess the unique ability to convert atmospheric nitrogen (N2) into ammonia (NH3) through a process known as nitrogen fixation. This is vital for plant growth because atmospheric nitrogen is not readily usable by most organisms. By converting nitrogen into forms that plants can absorb, such as ammonium and nitrate, bacteria play a crucial role in the nitrogen cycle, enhancing soil fertility and supporting ecosystems. The process is significantly facilitated by symbiotic relationships, particularly with legumes, where specific types of bacteria, like Rhizobium, establish nodules on the roots of these plants. This collaboration not only provides plants with essential nutrients but also contributes to a sustainable cycle of nutrient replenishment within the soil. Other options, like fungi, viruses, and algae, do not perform this function. While fungi are important for decomposing organic matter and recycling nutrients, they do not fix atmospheric nitrogen. Viruses are not living organisms that typically function in nutrient cycles but rather infect hosts. Algae can contribute to nutrient cycling and some species participate in the nitrogen cycle, but they do not fix atmospheric nitrogen in the same way that bacteria do. Thus, bacteria are uniquely positioned in this context to facilitate the conversion of