What is the best definition of diffusion?

random movement of molecules across a concentration gradient until the difference in concentration between two regions is near zero

a process in which molecules move across a semipermeable membrane until the number of molecules of water is nearly equal on both sides

net movement of molecules across a permeable membrane bilayer that requires transport proteins

the exchange of solute molecules across a permeable membrane from areas of high concentration to areas of low concentration

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.