Cell

The membrane system of a cell performs many important functions. This system controls the entrance and exit of substances into and out of the cell, and also provides for the manufacture and packaging of substances Figure 1. A plant cell. Photograph by Dr. Dennis Kunkel. Phototake. Reproduced by permission. within the cell. The membrane system of the cell consists of the plasma membrane, which encloses the cell contents; the endoplasmic reticulum, which manufactures lipids and proteins; the Golgi body, which packages substances manufactured within the cell; and various vesicles, which perform different functions.