The structure that controls what enters and leaves the cell is the cell membrane, also known as the plasma membrane. This membrane acts as a selective barrier, allowing certain substances to pass while blocking others.
The cell membrane is primarily composed of a double layer of phospholipids, with embedded proteins that assist in the transport of materials. The phospholipid bilayer’s hydrophobic (water-repelling) properties prevent polar molecules and ions from easily crossing the membrane. Instead, these substances require specific transport proteins to facilitate their movement.
Additionally, the cell membrane plays a crucial role in maintaining homeostasis by regulating the internal environment of the cell. It permits the entry of essential nutrients and the exit of waste products, ensuring that the cell functions optimally.
In summary, the cell membrane not only acts as a barrier but also as a gatekeeper, controlling the flow of substances in and out of the cell to maintain a stable internal environment.