Which organ controls the pituitary gland by producing chemicals that either stimulate or suppress hormone secretions by the pituitary gland?

A collection of specialized cells that is located in the lower central part of the brain, is the main link between the endocrine and nervous systems. Nerve cells in the hypothalamus control the pituitary gland by producing chemicals that either stimulate or suppress hormone secretions from the pituitary.

No you are not wrong

Being composed of one or more cells