Ten percent of energy is transferred from one level to the next level on the energy pyramid. What happens to the other 90% of energy? A. It is stored as fat. B. It is given off as heat. C. It is stored as a protein. D. It is used in reproduction.

The answer is B. I look at it this way: The bottom level of the pyramid contains the producers (the autotrophs), the plants. Next you have the herbivores (primary consumers), essentially. Mice and the like. Then there are the secondary consumers. Snakes. Finally, there are the Tertiary consumers. Hawks. Each level eats the level below it, to put it bluntly, but it cannot keep all of that energy, so there must be some waste. For animals, the waste product of living is heat (you give it off all the time).