membrane : A lipid bilayer along with all the proteins and protein complexes embedded in it an attached to it. ; integral component of membrane : The component of a membrane consisting of the gene products and protein complexes having at least some part of their peptide sequence embedded in the hydrophobic region of the membrane. ; cilium : A specialized eukaryotic organelle that consists of a filiform extrusion of the cell surface and of some cytoplasmic parts. Each cilium is largely bounded by an extrusion of the cytoplasmic (plasma) membrane, and contains a regular longitudinal array of microtubules, anchored to a basal body. ; cell projection : A prolongation or process extending from a cell, e.g. a flagellum or axon. ; plasma membrane : The membrane surrounding a cell that separates the cell from its external environment. It consists of a phospholipid bilayer and associated proteins. ; photoreceptor connecting cilium : The portion of the photoreceptor cell cilium linking the photoreceptor inner and outer segments. It's considered to be equivalent to the ciliary transition zone. ;