Rough Endoplasmic Reticulum

They are a continuous series of membrane-bound flattened sacs within the cell's cytoplasm. They have a rough outer appearance because of the protein-synthesizing particles called ribosomes on them.

__Smooth Endoplasmic Reticulum __

They are a meshwork of fine disklike tubular membrane vesicles within the cell's cytoplasm. They are involved in synthesizing and storing lipids, including cholesterol and phospholipids.

Ribosomes

The ribosome is a cytoplasmic structure that is minute and sphere-shaped. It is composed of protein and ribonucleic acid (RNA). They serve as the site of protein synthesis.