Why is far less energy available to top predators than to first level consumers in a food web?

Answer and Explanation:

Most of the food eaten by herbivores (primary consumers) passes through the digestive tract as undigested matter that is removed as faeces. Most of the absorbed food materials are used in respiration to release energy. Only a small proportion of the consumed food is incorporated into tissues of the consumer while the rest is lost through excretion. Only the food incorporated into the tissues can be passed on the top predators and secondary consumers.