Which thin flexible barrier separates the internal environment of the cell from the extracellular fluid?

Plasma membrane

The correct answer is Option (4) - Plasma membrane

The thin, flexible barrier that separates the internal environment of the cell from the extracellular fluid is called the plasma membrane. It is also commonly referred to as the cell membrane or cytoplasmic membrane. The plasma membrane is composed of a phospholipid bilayer embedded with proteins, cholesterol, and carbohydrates. This structure regulates the passage of substances in and out of the cell, controlling the movement of ions, nutrients, and waste products. Additionally, the plasma membrane plays crucial roles in cell signaling, cell recognition, and maintaining cell structure and integrity