Final answer:
The plasma membrane's functions include defining cell borders, controlling substance flow, allowing flexibility, and carrying markers for cellular recognition. The membrane consists of a phospholipid bilayer with embedded proteins that assist in transport and communication.
Step-by-step explanation:
General Functions of the Plasma Membrane
The plasma membrane, also known as the cell membrane, serves several critical functions for the cell. It defines the cell's borders, facilitates interaction with the environment, controls the entry and exit of substances, and provides flexibility for cells to change shape, especially important for red blood cells and white blood cells as they pass through narrow capillaries. The membrane's selective permeability is essential for maintaining homeostasis within the cell. Furthermore, the plasma membrane's surface is studded with marker molecules that are crucial for cellular recognition, a vital process for tissue and organ formation during development and for the immune system to distinguish between self and non-self.
Description of the Phospholipid Bilayer
The plasma membrane is composed primarily of a phospholipid bilayer, with the hydrophobic, fatty acid tails facing inward and the hydrophilic heads facing the external and internal aqueous environments. This structure forms a barrier that certain substances cannot readily cross without help from membrane proteins or transport mechanisms.
Other Molecules in the Plasma Membrane and Their Functions
Apart from phospholipids, the plasma membrane contains various proteins, including integral proteins and peripheral proteins. Integral proteins can span the entire membrane and are often involved in the transport of materials into and out of the cell, while peripheral proteins are found on the membrane's exterior or interior surfaces and can serve as enzymes, structural attachments, or recognition sites that play a vital role in immune function and cellular interaction.