文档介绍：Section E Membrane E1 Membrane lipid E2 Membrane protein E3 Membrane transport: small molecules E4 Membrane transport: macro- molecules A cell body (plasma and alveolar membranes tightly apposed) A cilium mitochondrion A digestive vacuole The endoplasmic reticulum A secretory vesicle Electron micrograph of the membranes of two adjacent cells 25 nm 1. Biomembranes anized, sheetlike assemblies consisting mainly of proteins and lipids The functions carried out by membranes are diverse and indispensable for life. Biomembranes form boundaries around the cell and aroud distinct partments. Biomembranes are highly selective permeability barriers with specific protein channels and pumps regulating the molecular and positions of the intracellular medium (transport across membranes).