Which plant group is capable of converting atmospheric nitrogen into a form usable by plants?

• A. Legumes
• B. Grains
• C. Roots
• D. Fungi

Answer: (A)

Nitrogen fixation occurs when atmospheric nitrogen is converted into forms plants can use, such as ammonia. Legumes form a special partnership with nitrogen-fixing bacteria (Rhizobium) inside root nodules. These bacteria take N2 from the air and convert it into ammonia, which the plant can use to make amino acids and proteins, improving soil nitrogen for future crops. Grains don’t fix nitrogen themselves, roots only absorb nitrogen from the soil, and fungi don’t typically fix atmospheric nitrogen for the plant.