One of the basic functions of a cell membrane is to act like a protective outer covering for the cell. Apart from this, there are many other important cell membrane functions, that are vital for the functioning of the cell. The following are some of the cell membrane functions. 1) Cell membrane anchors the cytoskeleton (a cellular 'skeleton' made of protein and contained in the cytoplasm) and gives shape to the cell. 2) Cell membrane is responsible for attaching the cell to the extracellular matrix (non living material that is found outside the cells), so that the cells group together to form tissues. 3) Another important cell membrane function is the transportation of materials needed for the functioning of the cell organelles. Cell membrane is semi permeable and controls the in and out movements of substances. Such movement of substances may be either at the expense of cellular energy or passive, without using cellular energy. 4) The protein molecules in the cell membrane receive signals from other cells or the outside environment and convert the signals to messages, that are passed to the organelles inside the cell. 5) In some cells, the protein molecules in the cell membrane group together to form enzymes, which carry out metabolic reactions near the inner surface of the cell membrane. 6) The proteins in the cell membrane also help very small molecules to get themselves transported through the cell membrane, provided, the molecules are traveling from a region with lots of molecules to a region with less number of molecules.