Which term describes the cycle that continuously circulates elements through ecosystems?

• A. Hydrologic Cycle
• B. Productivity
• C. Nutrient Cycles
• D. Ecotones

Answer: (C)

Elements essential to life move through ecosystems via nutrient cycles, the biogeochemical pathways that transport and transform elements like carbon, nitrogen, and phosphorus. Plants take up nutrients from soil and water, animals obtain them through food, and microbes decompose waste and dead matter, returning minerals to the environment so they can be reused. Energy, by contrast, flows in one direction, but nutrients cycle continuously, linking living communities with their physical surroundings. The other terms don’t describe this ongoing circulation: the hydrologic cycle is specific to water movement, productivity is the rate of biomass production, and ecotones are transitional zones between ecosystems.