2) explain what a target cell/tissue/organ is with respect to the endocrine system.

The specific distant organ which is affected by a specific hormone secreted by a  endocrine gland is called the target organ. For example, oxytocin secreted by the posterior pituitary affects the contraction of the walls of uterus resulting in parturition. Here, the uterine wall is the target organ.

Explanation:

Endocrine system is a system of ductless glads that secrete and pour chemical messengers into the blood and control various metabolic activities of the body.Hormones are  signal molecule that are produced by endocrine gland and are directly poured into the blood.According to current scientific definition : Hormones are  low molecular weight, chemically heterogeneous non-nutrient substances which produced in trace amounts and act as inter-cellular signal molecules.Even though blood distributes hormones throughout the body, only specific target cell can  respond to each hormone because only the target cell have receptors for binding with particular hormone.

That is true! many fish species traveled to the u.s. because of it.