Membranes are the barriers to or within the cell which separates the inside from the outside, prevents molecules inside the cell to leaking out and unwanted substances to diffuse in. The study of membrane biochemistry focuses on the all biochemical and bio physiological aspects of membrane structure and function and also their constituent protein and lipid components. Membrane, in biology, the thin layer that forms the outer boundary of a living cell or of an internal cell compartment. The outer boundary is the plasma membrane, and the compartments enclosed by internal membranes are called organelles. Biological membranes have three primary functions:  they keep toxic substances out of the cell;  they contain receptors and channels that allow specific molecules, such as ions, nutrients, wastes, and metabolic products, that mediate cellular and extracellular activities to pass between organelles and between the cell and the outside environment; and they separate vital but incompatible metabolic processes conducted within organelles