Ontario Grade 9 Science Class Practice Exam

What process turns organic nitrogen back into ammonium in the nitrogen cycle?

1. Denitrification

2. Ammonification

3. Assimilation

4. Nitrification

The correct answer is: Ammonification

Ammonification is the process by which organic nitrogen is turned back into ammonium in the nitrogen cycle. This process occurs when bacteria and fungi break down organic matter, such as dead plants and animals, and convert the nitrogen from proteins and wastes into ammonium. It is important to note that both denitrification and nitrification are processes that involve converting nitrogen, but they do not convert organic nitrogen back into ammonium. Denitrification converts nitrate back into atmospheric nitrogen gas, while nitrification converts ammonium into nitrate. Assimilation is the process by which plants and animals incorporate ammonium and nitrate into their tissues, but it does not involve the conversion of organic nitrogen into ammonium. Therefore, ammonification is the correct answer for this question.