d
(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 and nuclear membranes. It is the site of important metabolic reactions, including phospholipid and fatty acid synthesis. In animal cells lipid­like steroidal hormones are also synthesized.