Which part of the cell is semipermeable, or controls what enters and leaves the cell?

The right answer is cell membrane.

The cell membrane plays, through permeability, an important role in exchanges and transport between the cell and its environment. It consists of lipids (phospholipids, cholesterol), proteins (proteins associated with membranes) and carbohydrates. It distinguishes the cytoplasm of a cell, protecting it from the external environment.

hormones in blood stream

image: dtc.ucsf.edu

endocrine glands secrete hormones into the blood stream near them; the hormones then travel in our bloodstream until it reaches its destination, called a target cell, in distance parts of the body. in the target tissue, hormones lock onto the target’s plasma membrane, called the receptor site.

correct answer is a. and d.