A nutrient cycle refers to the movement and transformation of essential elements like carbon, nitrogen, and phosphorus within an ecosystem. Nutrient cycles involve various biological, geological, and atmospheric processes, enabling the transfer of nutrients through different forms and organisms over time. For example, in the carbon cycle, carbon dioxide is absorbed by plants during photosynthesis, incorporated into organic matter, and eventually returned to the atmosphere through respiration and decomposition. Understanding nutrient cycles is critical for maintaining ecosystem sustainability and soil fertility.