In the context of energy flow through ecosystems, what is the primary role of nutrients?

• A. They provide the main source of energy for all trophic levels.
• B. They are lost as heat at each trophic level.
• C. They are recycled within the ecosystem and used repeatedly by organisms.
• D. They are only used by producers and not by consumers.

Answer: (C)

Verified step by step guidance

1. Understand the context of the question: Energy flow and nutrient cycling are two distinct processes in ecosystems. Energy flows in one direction and is eventually lost as heat, while nutrients are recycled.
2. Clarify the role of nutrients: Nutrients are chemical elements (e.g., carbon, nitrogen, phosphorus) that organisms need to build tissues and carry out life processes. Unlike energy, nutrients are not lost but are reused within the ecosystem.
3. Analyze the options: The first option ('They provide the main source of energy for all trophic levels') is incorrect because nutrients are not a source of energy; energy primarily comes from the sun and is transferred through trophic levels via food chains.
4. Evaluate the second option ('They are lost as heat at each trophic level'): This is incorrect because it describes energy flow, not nutrient cycling. Nutrients are not lost as heat.
5. Confirm the correct answer: The correct option is 'They are recycled within the ecosystem and used repeatedly by organisms,' as this accurately describes the role of nutrients in ecosystems.