Hello scientific enthusiasts! I have recently been studying the ultrastructure of the cell particularly with endoplasmic reticuli. I understand that this classification of organelles is divided into the soft and rough groups which have their respective functions of cell detoxification, lipid synthesis and so forth. But according to several comparison charts in biology books and online resource websites endoplasmic reticuli are stating as being rarely absent in eukaryotic cells. However, the part about them being rarely absent is not explained. Therefore, I would be much obliged if someone could explain to me under what circumstances these organelles are absent from eukaryotic cells.

I do not know the answer to your question, but I wonder whether or not you mean protein synthesis, as opposed to lipid synthesis.