Answer
The smooth ER lacks ribosomes. It has various enzymes that aid in the synthesis of steroids, new phospholipids, etc. It also has enzymes that help with detox. These enzymes can add hydroxyl groups to many harmful substances and in this way they can be flushed from the body.
The rough ER has ribosomes. Ribosomes are the site of protein building. Proteins built at the rough ER are called secretory proteins that will need to be transported elsewhere. So the rough ER aids in the building and then transmission of those proteins. They are transmitted elsewhere via transport vesicles which are formed from ER material. Thus, the rough ER needs to have the ability to regenerate itself as vesicles leave. It does this by placing secretory proteins and phospholipids within its own membrane as needed.
Work Step by Step
Page 104 (Functions of Smooth ER) and page 105 (Functions of Rough ER)
