The cell is the fundamental unit of life and requires certain basic functions, including:
1. a boundary that distinguishes inside from outside the cell yet allows materials to enter or leave the cell.
2. an "engine" to capture energy from the environment and convert it to a form useful to the organism.
3. a genome that can be transmitted to the next generation and is stable, but able to change.
4. a way to change in response to environmental changes, over both a short (individual organism) and long (generational) time frame.

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.