In an ecosystem, energy _____, whereas chemical elements _____.

• A. remains constant; are lost
• B. is recycled; flow in one direction
• C. is created; are destroyed
• D. flows in one direction; are recycled

Answer: (D)

Verified step by step guidance

1. Understand the concept of energy flow in an ecosystem: Energy enters an ecosystem primarily through sunlight, which is captured by producers (like plants) during photosynthesis. This energy is then transferred through the food chain as organisms consume one another, but it is not recycled. Instead, energy is lost as heat at each trophic level, meaning energy flows in one direction.
2. Understand the concept of chemical element cycling: Unlike energy, chemical elements (such as carbon, nitrogen, and phosphorus) are recycled within an ecosystem. These elements move through biogeochemical cycles, which involve processes like decomposition, nutrient uptake by plants, and atmospheric exchange.
3. Compare the two processes: Energy flow is linear and unidirectional, while chemical elements are cycled repeatedly within the ecosystem.
4. Eliminate incorrect options: 'Energy remains constant; are lost' is incorrect because energy is not constant—it flows and is lost as heat. 'Energy is recycled; flow in one direction' is incorrect because energy is not recycled—it flows in one direction. 'Energy is created; are destroyed' is incorrect because energy cannot be created or destroyed (law of conservation of energy), and chemical elements are not destroyed—they are recycled.
5. Select the correct answer: Based on the explanations above, the correct answer is 'flows in one direction; are recycled.'