PLEASE HELP ASAP

A specific immune response begins when a white blood cell comes in contact with an antigen (any substance that the immune system does not recognize as part of the body). What external factor typically triggers a specific immune response?

A. an invasion of a microorganism from the external environment
B. a fluctuation of the external air pressure
C. a large release of adrenalin by the endocrine system
D. a change in the external temperature

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.

How are gross production and net production different? a. net production is always greater than gross production. b. net production is always less than gross production. only animals have net production. d. only plants have net production. select the best answer from the choices provided

Which cell organelle is the site for photosynthesis? a. chloroplast b. endoplasmic reticulum c. golgi apparatus d. lysosome