Ecology Practice Exam 2025 – Comprehensive Prep for Certification

The process that returns nitrogen to the soil from organic matter is decomposition. During decomposition, microorganisms break down dead plants, animals, and other organic materials. This breakdown releases nitrogen, which was previously part of the organic matter, back into the soil in forms that can be utilized by plants. It is a crucial part of the nitrogen cycle, as it ensures that nitrogen is recycled through ecosystems, making it available for new plant growth.

In contrast, nitrogen fixation is the process by which certain bacteria convert atmospheric nitrogen into forms that plants can use, but it does not directly involve the breakdown of organic matter. Denitrification is a process where nitrates in the soil are converted back into nitrogen gas, which is released into the atmosphere, thereby removing nitrogen from the soil rather than returning it. Absorption refers to the uptake of nutrients and water by plants from the soil, which does not involve returning nitrogen from organic matter to the soil.