The "endosymbiont theory" states that eukaryotic cells work together to form a multicellular organism.

2. cells are the basic units of structure and function in living things ... Cell theory states that ... structure that contains genetic material in the form of DNA and controls many of the cell's activities. eukaryotic to maintain homeostasis multicellular organisms. ... group of organs that work together to perform a specific function.

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.