Is it true that decomposers are the source of energy for an energy pyramid??
Decomposers are not so important relative to putting energy back into the ecosystem. Rather, the decomposers free up minerals and other things required for the growth of most other members of the ecosystem. In terrestrial ecosystems, the source of energy is the sun. The kinetic energy of sunlight is trapped in the chemical bonds of sugar molecules during photosynthesis. Some of those molecules, such as cellulose, are broken down by the decomposers, releasing the carbohydrates back into the ecosystem. As for the second question, energy transfer between different trophic levels of an ecosystem is very inefficient, with most of the energy (about 80%) lost as heat (inceasing the entropy of the universe as the laws of physics demand).
