When an herbivore eats a plant, what happens to 90% of the energy obtained from that plant?

I believe that about 90% of the energy obtained from the plant is lost inform of heat energy. The total energy passed from one level to the next is only about one-tenth of the energy received from the previous organism. This means that herbivores will only get about ten percent of the energy that the plant gets from the sun. The remainder of the plant's energy is unusable as energy by the animal. Therefore, as you move up the food chain, there is less energy available.