Assertion: The loss of biologically useful energy as heat with every energy transfer in a food chain is a consequence of the second law of thermodynamics.
Reason: Energy does not remain trapped permanetly in any organism. It is either passed on to higher trophic level or becomes available to detritivores and decomposers after the organism dies.

Answer

B

Explanation

According to second law of thermodynamics, every activity involing energy transformation is accompanied by dissipation of energy. In other words, the loss of biologically useful energy as heat with every energy transfer in a food chain is a consequence of the second law of thermodynamics. Every time energy is transferred from one place to another or transformed from one kind to another, some of it is converted into heat. An organism transfers chemcial energy from to the chemical glucose or fatty acids to ATP (cellular respiration ) and then to the chemical bonds of new molecules (during molecular synthesis), and transforms chemical energy into activ transport of molecules, muscle contractions, and a variety of other activities, which are essential to life. Because every living organism continuously converts chemical energy into heat, there is always a loss of chemical energy with each step in a food chain.
Energy does not remain trapped permanently in any organism. It is either passed on to the higher trophic level or becomes available to detrivores and decomposers after the organism dies. Death of organism is the beginning of the detritus food chain/web.