A student puts drops of Lugol's iodine solution into the water in the beaker shown. The water turned red. After a short time, the starch solution inside the dialysis tubing turned black. Which function of the cell membrane was the student demonstrating?

Cell membrane as  a semi permeable membrane.

Explanation

A semi permeable membrane is the one that would only allow water,ions  and certain molecules to pass through it  by diffusion while restricting other  large molecules from passing through.

Details in the attachment.

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.