ER stands for endoplasmic reticulum. It is a eukaryotic organelle. Within cells, it is a network within cells of vesicles, cisternae and tubules.
The Rough ER, or Rough endoplasmic reticulum, synthesizes proteins. The Smooth ER, on the other hand, does quite a lot. It synthesizes steroids and lipids, metabolizes carbohydrates and steroids, and regulate calcium concentration, among other things.
Thus functionally, they both produce. The rough ER produces proteins and the smooth ER produces steroids and lipids.
Structurally, both look like a system of tubes or sacs. The rough ER is studded with ribosomes, which make the proteins, and that’s what gives it the name rough. The smooth ER is not.
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