Which group of living things can move energy from consumers at the top of an energy pyramid back to producers at the bottom? *

Answer is Decomposers

In any food chain autotrophs are producers which is makes food with the help of sun energy. Primary consumers are herbivores which eat plants, and secondary and tertiary consumers are carnivores which feed on primary consumers. On the death of producers and consumers, decomposers such as bacteria and fungi, breakdown dead animal, dead plant materials and waste products from other members of the ecosystem into simple soluble nutrients. These nutrients return to the soil from dead organic matter. Thus, the living things depends on decomposition processes at the end of the chain by decomposers.  

what school and grade?

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.