The role of nitrogen-fixing bacteria in the nitrogen cycle is to convert atmospheric nitrogen (N2) into ammonia (NH3), a form that plants can utilize. These bacteria, often found in nodules on the roots of legumes, play a crucial part in replenishing nitrogen levels in the soil, which is essential for plant growth and development. Through mutualistic relationships, these bacteria provide plants with necessary nutrients while benefiting from carbohydrates produced by the plants. Their activity not only enhances soil fertility but also supports overall ecosystem health by maintaining the nitrogen cycle.