Answer:
We divide ER into two types because Smooth ER(SER) do not have ribosomes and Rough ER(RER) have ribosome thus former is also called Agranulated ER and Latter is called Granulated ER. SER is not involved in protein synthesis its main function is synthesis of lipids carbs steroid thus it is found in Adipose cells, interstitial cells, liver cells. RER have ribosomes so they are involved in protein synthesis so they are present in protein synthesising cells such as salivary glands and pancreas.