A Level Biology Practice Exam

What is the role of the plasma membrane in a cell?

1. To facilitate energy production

2. To provide structural support

3. To regulate the movement of substances in and out of the cell

4. To store genetic information

The correct answer is: To regulate the movement of substances in and out of the cell

The plasma membrane plays a crucial role in maintaining the homeostasis of the cell by regulating the movement of substances in and out of it. This semi-permeable barrier is essential for protecting the internal environment of the cell and ensuring that necessary nutrients enter while waste products exit. The membrane is composed of a phospholipid bilayer with embedded proteins that facilitate transport processes, including passive diffusion, facilitated diffusion, and active transport. These functions are vital for the cell’s survival, allowing it to interact with its external environment, communicate with other cells, and maintain a stable internal condition, despite changes in the external environment. The other roles mentioned, such as energy production, structural support, and the storage of genetic information, are carried out by different cellular components. For instance, mitochondria are primarily responsible for energy production, while the cytoskeleton provides structural support, and the nucleus is the site for storing genetic information. Thus, the specific role of the plasma membrane is fundamentally about regulating substance movement according to the cell's needs.