One of the challenges faced by all living things, be they amoebae or humans, is to separate their internal environment from the external environment. Critical nutrients must get into the cells, and waste must get out. To make matters more complex, cells need to be able to regulate that movement, letting the materials cross sometimes and preventing them from crossing at others. Another challenge is finding a way for cells to communicate with each other. The solution to these challenges lies in the properties of the cell membrane (also called the plasma membrane). This delicate structure is essential to the life of cells. When the membrane loses its ability to carry out these processes, the cell dies.