The pathway through which nutrient are replenished and circulated in an ecosystem is called a

Step 1: Analyze the question The question asks about the pathway through which nutrients are replenished and circulated in an ecosystem. The key words are "replenished" and "circulated," which suggest something that repeats and returns materials to where they started.

Step 2: Explain the concept Nutrients such as carbon, nitrogen, water, and phosphorus are not lost from an ecosystem. They move repeatedly between living things (plants, animals, decomposers) and the non-living environment (soil, air, water). This repeated movement is called a biogeochemical (nutrient) cycle. Examples include the carbon cycle, nitrogen cycle, water cycle, and phosphorus cycle.

Step 3: Check each option

• A. Cycle: Nutrients are taken up from the environment, passed through organisms, and returned by decomposition and excretion. This matches "replenished and circulated."
• B. Pyramid of energy: This shows how much energy is available at each trophic level. It does not show nutrient circulation, and energy flows in one direction rather than being recycled.
• C. Pyramid of numbers: This shows how many organisms are at each trophic level. It has nothing to do with nutrient movement.
• D. Food chain: This shows who eats whom and the one-way transfer of energy. It is a feeding sequence, not a replenishing loop.

Step 4: Answer The correct option is A. cycle.

Exam tip: Remember "Energy flows, nutrients cycle." Energy moves in one direction (sun → producers → consumers, lost as heat), but nutrients go round and round. If a question mentions "replenished," "recycled," or "circulated," think cycle.