Ontario Grade 9 Science Class Practice Exam

Which of the following is not a step in the nitrogen cycle?

1. Photosynthesis

2. Nitrogen fixation

3. Denitrification

4. Assimilation

The correct answer is: Photosynthesis

Photosynthesis is not a step in the nitrogen cycle because it is a process that occurs in plants, not in the nitrogen cycle. Photosynthesis is the process by which plants convert sunlight, carbon dioxide, and water into glucose and oxygen. In contrast, the nitrogen cycle is the process by which nitrogen is converted into various forms that can be used by living organisms. The other options, nitrogen fixation, denitrification, and assimilation, are all important steps in the nitrogen cycle, which involve different types of bacteria and processes that convert nitrogen in the atmosphere into forms that can be used by living organisms. Therefore, A is the correct answer because it is not a step in the nitrogen cycle.