Nutrients behave differently to energy in ecology. Energy flows from one organism to another, and is eventually all transmitted to the environment as heat. From the environment it is lost to space. Energy transfer is therefore a linear process.
Nutrients behave differently to energy, because nutrients can be reused. This is because the elements involved remain the same as they pass from organisms to the environment and back again. The passage of nutrients therefore is cyclical, as they can be used, recycled and reused indefinitely.
All nutrients have their own cycle. At A-level the two that are examined in detail are carbon and nitrogen.