Which structure in the cell is responsible for regulating what enters and exits?

The cell membrane is the structure responsible for regulating what enters and exits the cell. It functions as a selective barrier, meaning it controls the movement of substances into and out of the cell. This is achieved through its semi-permeable nature, allowing certain molecules to pass while restricting others. The cell membrane is composed of a lipid bilayer, integrated with proteins that can facilitate transport, signaling, and other crucial functions related to cellular communication and homeostasis.

In this way, the cell membrane plays a vital role in maintaining the internal environment of the cell, enabling it to respond to changes in its external environment while ensuring that essential molecules such as nutrients and ions can enter, and waste products can be expelled.