Which of the following diagrams correctly illustrates the nitrogen cycle?

• A. A diagram showing nitrogen fixation, nitrification, assimilation, ammonification, and denitrification as processes cycling nitrogen between the atmosphere, soil, and living organisms.
• B. A diagram illustrating the water cycle, including evaporation, condensation, and precipitation.
• C. A diagram depicting the flow of energy from the sun to producers and then to consumers.
• D. A diagram showing only the movement of carbon dioxide and oxygen between plants and animals.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the nitrogen cycle. The nitrogen cycle is a biogeochemical process that describes how nitrogen moves through the atmosphere, soil, and living organisms. Key processes include nitrogen fixation, nitrification, assimilation, ammonification, and denitrification.
2. Step 2: Nitrogen fixation is the process where atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or related compounds by bacteria or through industrial processes. This makes nitrogen available to plants.
3. Step 3: Nitrification is the conversion of ammonia into nitrites (NO₂⁻) and then into nitrates (NO₃⁻) by soil bacteria. Nitrates are a form of nitrogen that plants can absorb and use.
4. Step 4: Assimilation occurs when plants absorb nitrates from the soil and incorporate them into organic molecules like amino acids and proteins. Animals then obtain nitrogen by consuming plants or other animals.
5. Step 5: Ammonification and denitrification complete the cycle. Ammonification is the conversion of organic nitrogen back into ammonia by decomposers. Denitrification is the process where bacteria convert nitrates back into nitrogen gas (N₂), releasing it into the atmosphere.