Final answer:
The cell membrane is a semipermeable lipid bilayer that surrounds and protects the cell while controlling the passage of substances in and out due to its selective permeability.
Step-by-step explanation:
What is the Cell Membrane?
The cell membrane, also referred to as the plasma membrane or plasmalemma, is a semipermeable lipid bilayer that forms the boundary of all cells. It is a thin, flexible barrier that separates the cell's intracellular fluid (ICF) from the extracellular fluid (ECF), effectively controlling the movement of substances in and out of the cell. Comprised of two adjacent layers of phospholipids with hydrophobic internal lipid tails and hydrophilic external phosphate heads, it includes a variety of proteins and other lipids, such as cholesterol, that facilitate cellular processes and provide structural support.
One critical feature of the cell membrane is its selective permeability. This property allows certain molecules to pass through the membrane while excluding others, thereby maintaining the internal environment of the cell. This selection depends on the size, charge, and solubility of the molecules in relation to the lipid bilayer's characteristics and the specific transport proteins present in the membrane.
Therefore, the cell membrane is not just a static barrier but a dynamic structure that plays an essential role in the life of the cell, including transport functions, signal transduction, and cell-to-cell communication.