The DNA in some lung cells was damaged by the carcinogenic compounds in tobacco and apoptosis was initiated. Which of the following is the best way for the damaged lung cells to send a message to their neighboring cells that they need to increase the production of DNA repair enzymes or start apoptosis as well? They should send signaling molecules into the bloodstream.
They should send signaling molecules through the gap junctions.
They should send signaling molecules across a small extracellular space.
They should send signaling molecules by secreting them into the local environment.

Which is an advantage of having memory cells when a pathogen is encountered for a second time. a) the memory cells are what proliferate into clones of cells in response to the binding of an antigen. b) memory cells are vital to the primary immune response in that they immediately recognize pathogens even at the first encounter. c) memory cells are essentially effector cells that are short lived and attack antigens even without having a receptor specific to that antigen. d) it ensures that more lymphocytes with a receptor specific to a particular antigen will be present than in a host that had never encountered that pathogen.