Imagine you have a five-step food chain. If 100 percent of the energy is available at the first trophic level, what percentage of energy is available at the highest trophic level?

0.1% will be available at the highest trophic level

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.