What is the main purpose of the plasma membrane?

The main purpose of the plasma membrane is to regulate the entry and exit of substances into and out of the cell. It acts as a selective barrier that controls what can pass through based on size, charge, and solubility. This regulation is crucial for maintaining the internal environment of the cell, allowing the cell to take in necessary nutrients and remove waste products, thereby ensuring proper cellular function. The structure of the plasma membrane, which includes a phospholipid bilayer with embedded proteins, facilitates this selective permeability. This ability to control the cellular environment is fundamental to cellular homeostasis and overall cell health.

While options related to energy production, protecting DNA, and storing nutrients are important cellular functions, they do not primarily describe the function of the plasma membrane. Energy production occurs mainly in cellular organelles, such as mitochondria; protecting DNA is primarily the role of the nuclear membrane; and nutrient storage is typically managed by various types of cellular organelles or inclusions, rather than the plasma membrane itself.