Final answer:
The characteristic of the endocrine system that is incorrect is 'a. Chemical messenger travels a short distance,' because hormones travel through the bloodstream over long distances to reach their target cells. the correct option is (a).
Step-by-step explanation:
Which of the following is not a characteristic of the endocrine system? The correct answer is 'a. Chemical messenger travels a short distance.' The endocrine system involves hormones that are released into the bloodstream and travel long distances to reach target cells that contain specific receptors for these hormones, affecting their function. This is in contrast to neurotransmitters, which do travel short distances to act on neighboring cells. Effector tissues of hormones indeed include virtually all tissues, and receptors for hormones are found either on the plasma membrane or within target cells.
Therefore, option 'a' is the characteristic that does not belong to the endocrine system as it describes a function more typical of neurotransmitters and the neural communication system.