What are the primary functions of a cell membrane?

The primary functions of a cell membrane focus on both protecting the cell and regulating the movement of substances in and out of the cell. The cell membrane, also known as the plasma membrane, serves as a barrier that separates the internal environment of the cell from the external surroundings. This functional structure is selective permeable, meaning it controls what enters and exits, thereby maintaining the appropriate conditions for cellular processes.

The membrane is composed of a phospholipid bilayer, which provides fluidity and flexibility while also containing various proteins that facilitate transport and communication. The ability to maintain homeostasis is crucial for the survival of the cell, allowing it to respond to changes in the environment through the controlled passage of ions, nutrients, and waste products.

In contrast, other options describe functions that are not primarily associated with the cell membrane. Energy production and storage are mainly performed by organelles like mitochondria. DNA synthesis and reproduction involve genetic material and processes like mitosis, neither of which occur at the membrane level. Nutrient absorption and waste elimination are processes relevant to the functioning of the membrane, but they are more specific outcomes of the membrane’s regulatory role rather than primary functions on their own. Thus, the correct answer emphasizes the dual aspects of protection and regulation of movement that