The endomembrane system contains certain substances and processes within membrane-bound compartments. These compartments are continuous with one another or are connected by movements of sacs of membrane called vesicles. Rough endoplasmic reticulum (ER) has ribosomes on its outer surface and transports and processes proteins. Smooth ER lacks ribosomes and among its functions is the manufacturing of phospholipids. The Golgi body (apparatus) receives and produces vesicles. Lysosomes contain concentrated mixtures of digestive enzymes. They break down old organelles and are involved in cell death.