Which cellular structure plays a key role in isolating the cytoplasm from the external environment?

The plasma membrane is crucial for isolating the cytoplasm from the external environment. It is a phospholipid bilayer that surrounds the cell, providing a barrier that separates the inside of the cell from its surroundings. This selective permeability allows the plasma membrane to control the movement of substances in and out of the cell, ensuring that essential molecules can enter while waste products can be expelled.

Additionally, the plasma membrane contains various proteins that facilitate communication and transport processes, contributing to cell signaling and maintaining the internal environment of the cell. Therefore, its primary role is to maintain the integrity of the cell and regulate interactions with the external environment, making it fundamental to cellular function.