Final answer:
The least amount of energy transferred in a food web is from secondary consumer to primary consumer because energy transfer is not in reverse order in natural ecosystems.
Step-by-step explanation:
The least amount of energy is transferred in a food web from secondary consumer to primary consumer (Option B). This is because energy transfer in ecosystems typically goes from producers to primary consumers (herbivores), then to secondary consumers (carnivores or omnivores that eat herbivores), and so on. Energy transfer is not in reverse order; therefore, secondary consumers do not transfer energy to primary consumers.
In a food web, energy is mostly lost through metabolic processes such as respiration, excretion, and as heat. The Energy Pyramid illustrates this concept, showing that a large amount of energy is lost at each step, from one trophic level to the next, mainly due to the second law of thermodynamics, which drives energy towards entropy and results in substantial loss as metabolic heat.
Studies by Howard T. Odum in the Silver Springs ecosystem provide empirical data on energy transfer: from primary producers to primary consumers, only a fraction of the energy is transferred, and from primary consumers to secondary consumers, even less is transferred. It follows that the transfer from secondary to primary consumers, which does not naturally occur in a food web, would be nonexistent.