Which of the following is not membrane-bound?
Membrane-bound organelles derive from endomembrane system involving lipid bilayers enclosing aqueous lumen, including nucleus surrounded by double membrane perforated by pores, mitochondria with outer and inner membranes supporting oxidative phosphorylation, endoplasmic reticulum network, Golgi stacks and lysosomes that are acidic hydrolase containing vesicles. Ribosomes represent exception being ribonucleoprotein particles approximately twenty five to thirty nanometers composed of ribosomal RNA and seventy to eighty proteins without delimiting membrane. Free cytosolic ribosomes translate cyto
Ref: Alberts Ch 12; ribosomes non-membranous RNPs 25-30nm, free and rough ER bound, no lipid bilayer.
