Membranous organelles are surrounded by what?

Membranous organelles are surrounded by lipid membranes. These lipid membranes, primarily composed of phospholipids, form the fundamental structure of cellular membranes, including those of organelles such as the endoplasmic reticulum, Golgi apparatus, mitochondria, and lysosomes. This lipid bilayer serves several critical functions, including creating a barrier that separates the internal environment of the organelle from the cytoplasm, facilitating compartmentalization within the cell, and allowing for the proper organization and function of various biochemical processes.

The lipid structure is vital because it possesses hydrophilic (water-attracting) heads and hydrophobic (water-repellent) tails, which enable the formation of the bilayer that is both functional and stable. This organization allows for the passage of certain molecules while restricting others, contributing to the selective permeability of cell organelles. The role of these membranes in cellular structure and function is fundamental in maintaining homeostasis within the cell.