| − | A membrane is any layer that separates two [[Fluid|fluids]]. Membranes may be [[Semipermeable Membrane|selectively permeable]], meaning they allow some molecules across the membrane, but block others. Dialysis tubing is an example of this. Most membranes in biology are [[lipid bilayer|lipid bilayers]]. This means they consist of two layers of interposed [[Lipid|lipids]]. | + | A '''membrane''' is any layer that separates two [[Fluid|fluids]]. Membranes may be [[Semipermeable Membrane|selectively permeable]], meaning they allow some molecules across the membrane, but block others. Dialysis tubing is an example of this. Most membranes in biology are [[lipid bilayer|lipid bilayers]]. This means they consist of two layers of interposed [[Lipid|lipids]]. |