Why is the nitrogen cycle important to humans?

• A. It produces oxygen necessary for human respiration.
• B. It converts atmospheric nitrogen into forms usable by plants, which are essential for human food production.
• C. It breaks down toxic metals in the soil, making them harmless to humans.
• D. It regulates the Earth's temperature by trapping heat in the atmosphere.

Answer: (B)

Verified step by step guidance

1. Understand the nitrogen cycle: The nitrogen cycle is a biogeochemical process that converts nitrogen from the atmosphere into forms that can be used by living organisms, and then back into atmospheric nitrogen. This cycle is essential for maintaining life on Earth.
2. Recognize the role of nitrogen in plants: Nitrogen is a critical component of amino acids, proteins, and nucleic acids, which are necessary for plant growth and development. Plants cannot directly use atmospheric nitrogen (N₂), so it must be converted into usable forms like ammonium (NH₄⁺) or nitrate (NO₃⁻).
3. Identify the importance to humans: Humans rely on plants for food, either directly (eating plants) or indirectly (eating animals that consume plants). The nitrogen cycle ensures that plants have access to nitrogen in forms they can use, which supports agricultural productivity and food security.
4. Clarify the process of nitrogen fixation: Atmospheric nitrogen is converted into usable forms primarily through nitrogen-fixing bacteria, which live in the soil or in symbiotic relationships with plant roots (e.g., legumes). This process is vital for replenishing nitrogen in ecosystems.
5. Eliminate incorrect options: The nitrogen cycle does not produce oxygen, break down toxic metals, or regulate Earth's temperature. Its primary importance lies in converting atmospheric nitrogen into forms usable by plants, which are essential for human food production.