There are two forms of endoplasmic reticulum (er) found in a cell. they are the rough and the smooth er. what does the rough er do in a cell?

RER is involved in protein synthesis, folding, transport and modification.

Explanation:

The Endoplasmic Reticulum is an organnelle found in eukaryotic cells. They are of two types; Rough Endoplasmic Reticulum and Smooth Endoplasmic Reticulum, so named based on the appearance of their surface. The Rough Endoplasmic Reticulum (RER) obtains it rough appearance from the membrane bound ribosomes attached to it.

Due to the ribosomes that attach to them during protein synthesis, their function is very much associated with protein synthesis. They are primarily involved in protein production, which would either remain in their lumen for further modification/processing called Glycosylation (adding sugar to proteins to form glycoproteins) or be transported through secretory vesicles to the Golgi apparatus. They also fold this proteins in their inner membrane structure called cisternae.

substitution is the answer in this case