IB Psychology – Biological Approach Practice Test

The idea being tested is that cells that respond to a hormone signal are called target cells. Hormones travel through the bloodstream as chemical messengers, but only cells with the specific receptors for that hormone will respond. The receptor acts like a lock for the hormone’s key, so binding triggers a cellular response—altering gene activity, enzyme function, or transport—specific to that cell’s machinery. This is why a single hormone can affect multiple tissues differently, depending on which cells have the right receptors. It’s distinct from endocrine glands (the organs that release the hormones), pheromones (signals to other individuals), and hormones themselves (the signaling molecules).