Question

the following diagram describes the nitrogen cycle. arrow 4 shows nitrogen moving from the atmosphere to microorganisms in the soil and plant roots. which process is represented by arrow 4? choose 1 answer: a nitrogen fixation b ammonification c nitrification d denitrification

Explanation:

To determine the process of Arrow 4, we analyze each option:

• Option A (Nitrogen Fixation): Nitrogen fixation is the process where atmospheric \( \text{N}_2 \) is converted into forms (like \( \text{NH}_3 \)) usable by plants/microorganisms. Arrow 4 shows \( \text{N}_2 \) moving from the atmosphere to soil microorganisms and plant roots, matching nitrogen fixation.
• Option B (Ammonification): Involves decomposers converting organic nitrogen to \( \text{NH}_4^+ \) (Arrow 3), not atmospheric \( \text{N}_2 \) to organisms.
• Option C (Nitrification): Converts \( \text{NH}_3/\text{NH}_4^+ \) to \( \text{NO}_2^-/\text{NO}_3^- \) (Arrow 2), not atmospheric \( \text{N}_2 \) uptake.
• Option D (Denitrification): Converts \( \text{NO}_3^- \) back to \( \text{N}_2 \) (by denitrifying microbes), opposite of Arrow 4.

Answer:

A. nitrogen fixation