(d) : Smooth endoplasmic reticulum (SER) is a system of smooth membranes (i.e., membranes not having ribosomes) within the cytoplasm of plant and animal cells. It forms a link between the cell andnuclear membranes. It is the site of important metabolic reactions, including phospholipid and fatty acid synthesis. In animal cells lipid-like steroidal hormones are also synthesized.