Cell membrane function

Cell Membranes enclose the entire cell, the nucleus, and all the organelles. The membranes hold the cell and each of its parts together.
Most membranes consist of a double layer of a fatty substance called phospholipid. Proteins occur at various points and extend to different depths within the double layer of phospholipids.
Only needed materials can enter the cell and its parts because of the structure and chemical composition of the membranes.