Answer:
The cell membrane is one of the great multi-taskers of biology. It provides structure for the cell, protects cytosolic contents from the environment, and allows cells to act as specialized units. A membrane is the cell’s interface with the rest of the world - it’s gatekeeper, if you will. This phospholipid bilayer determines what molecules can move into or out of the cell, and so is in large part responsible for maintaining the delicate homeostasis of each cell.
Explanation:
Cell membranes are semipermeable, meaning they have control over what molecules can or cannot pass through. Some molecules can just drift in and out, others require special structures to get in and out of a cell, while some molecules even need an energy boost to get across a cell membrane. Each cell’s membrane contains the right mix of these structures to help that cell keep its internal environment just right.