Question: which of these organelles is not made of or surrounded by a membrane?
Answer: Some of these organelles are not surrounded by a membrane and are called non-membranous organelles, such as ribosomes and centrosome. Other organelles are surrounded by a membrane and are called membranous organelles, such as endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, vacuoles, and plastids.