In order to survive, organisms must maintain stable conditions in their bodies, even though their external environments are always changing. for example, humans need to maintain an internal temperature around 37°c. blood needs to have a ph around 7.4 and an oxygen saturation close to 100%. what needs to happen in order to maintain these conditions? a) organ systems must interact with one another. b) organisms must be at rest. c) genes must be altered each time cells replicate. d) all of these.