Ontario Grade 9 Science Class Practice Exam 2025 - Free Grade 9 Science Practice Questions and Study Guide

Nitrification follows nitrogen fixation in the nitrogen cycle. Nitrogen fixation is the process of converting atmospheric nitrogen into a usable form for plants and other organisms. Nitrification is the process of converting ammonia or ammonium into nitrate, which is the form of nitrogen that plants can absorb and use. It is an essential step in the nitrogen cycle, as it provides a readily available source of nitrogen for plant growth. Assimilation, ammonification, and denitrification are all important processes in the nitrogen cycle, but they occur after nitrification. Assimilation is the process of incorporating nitrogen into organic compounds, ammonification is the process of converting organic nitrogen into ammonia, and denitrification is the process of converting nitrate back into atmospheric nitrogen. Therefore, nitrification is the correct answer as it occurs immediately after nitrogen fixation.