This delicate structure is essential to the life of cells. The solution to these challenges lies in the properties of the cell membrane ( plasma membrane).
Cells in the brain, for example, need to be able to tell cells in the heart to beat faster. Another challenge is finding a way for cells to communicate with each other. To make matters more complex, cells need to be able to regulate that movement, letting the materials cross at some times and preventing them from crossing at others. Critical nutrients must get into the cells and wastes must get out. One of the challenges faced by all living things, be they amoebae or humans, is to separate their internal environment from the external environment.