Which organisms recycle the organic molecules of dead organisms at all trophic levels and return their nutrients to the environment?

Decomposers recycle all the organic molecules of all the dead organisms, by breaking them down and make these nutrients available to the environment, which can now be used as the source of energy for other organisms. Decomposers can be bacteria, fungi or invertebrates. 

answer: - b cells

explanation: -

there are many types of white blood cells present in our body. one such class of white blood cells are the lymphocytes. the b cells belong to the lymphocyte class of wbcs. the b cells perform their action against the pathogen by producing specialised proteins called as antibodies. these antibodies are produced as and when the b cells encounter pathogens in response to the antigens present on the surface of the pathogen. these antibodies bind to the antigens present on the pathogen and then, target them for destruction by other cells of the immune system.

so, the b cells mediate their action by identifying the antigens present on the surface of the pathogens and then producing antibodies in return to mediate its effect.