In order for matter to recycle and return in the food chain shown here, what must be present at level a?

For matter to be recycled and returned to the food chain, decomposers must be present. Decomposers are the final link in a food chain. They play a very important role in the food chain and makes it a cyclic process. They eat up dead animals and plants and produce nutrients from these matter back to the food chain. Plants needs nutrients for growth while living animals take up the nutrients they need from eating plants. The nutrients from these living organisms are recycled back to the ecosystem when they die by the process called decomposition with the help of decomposers.