What are the structural and functional differences between rough and smooth ER? Why do cells of the testes and adrenal glands have large amounts...

Rough and smooth ER (endoplasmic reticulum) differ in that the rough ER has ribosomes on it.  These take the Messenger RNA and transcribe it into proteins which then enter the space inside the rough ER.  Smooth ER does not have ribosomes and is where steroids are made, which is why there is a lot of smooth ER in cells of the the adrenal gland and sex organs which produce steroid hormones such as estrogen and testosterone.