Lysosomes are single membrane bound vesicles which contain hydrolytic enzymes. They are believed to be formed by the joint activity of ER and Golgi complex. Precursors of hydrolytic enzymes are synthesised at RER and are transferred to the forming face of Golgi complex. These precursors are then changed to enzymes. Enzymes are then packed in larger vesicles and are pinched off at maturing face. These vesicles combine with endosomes to produce lysosomes