The cell membrane is the boundary that envelops all cells and provides a semipermeable barrier for their separation from the extracellular environment. It is constituted by a 5–8-nm-thick lipid bilayer – mainly composed of amphiphilic phospholipids – in which membrane proteins are interspersed. The cell membrane is involved in different cellular processes including active and passive traffic of substances, signal transduction, and cell adhesion and fusion. In addition to the cell membrane, inside the eukaryotic cytoplasm, there are membrane-enclosed organelles. These specialized compartments include the nucleus, mitochondria, plastids, Golgi apparatus, vacuoles, vesicles, lysosomes, peroxisomes, and endoplasmic reticulum. Mitochondria, present in almost all eukaryotes, and plastids, present in photosynthetic eukaryotes, are double-membrane organelles, a feature indicative of their endosymbiotic origin. Bacteriaand archaea lack...