Secretory proteins are

A. produced by ribosomes on the smooth endoplasmic reticulum

B. chemically modified in the nucleus

C. produced by the cell for internal use

D. released from the cell through the plasma membrane

E. incorporated into the mitochondrial membrane

D. released from the cell through the plasma membrane

Explanation:

Secretory proteins are produced in the rough endoplasmic reticulum from where it enters into the Golgi apparatus. In the Golgi apparatus, these proteins are modified and packed into the vesicles.

From the Golgi apparatus these secretory protein reaches the plasma membrane and release out of the cell through the membrane. These secretory proteins can be a hormone, antimicrobial peptides, enzymes, etc. They are called secretory protein because they are secreted to the extracellular region of the cell. Therefore the correct answer is D.