Explanation:

Rough endoplasmic reticulum (RER) looks rough when seen under the microscope because of the presence of ribosomes, i.e. they are present as nodules on the outer membrane of the rough endoplasmic reticulum. Ribosomes are the organelles that convert mRNA into proteins. These proteins are initially long strings of the amino acids. This string has to be folded in the right way to make a functional protein. The Rough endoplasmic reticulum (RER) helps with the folding of these amino acidstrings and at the same time prevents their degradation by enzymes in the cell. Because of this cooperation, the ribosomes can be attached to the ER. The ribosomes can then synthesize the amino acid string straight into the ER, making the process safer and more efficient