Kaplan Nursing Entrance Practice Exam

The plasma membrane is primarily composed of a lipid bilayer, mainly formed by phospholipids, with embedded proteins. This structure allows it to function as a selectively permeable barrier, which means it regulates the entry and exit of substances, thus maintaining homeostasis within the cell. It acts as a mediator between the internal environment of the cell and the external environment, facilitating communication and signaling through its receptors.

While phospholipids are critical to the structural integrity of the plasma membrane, the statement regarding the cytochrome chain of oxidative phosphorylation is indeed false. The cytochrome chain, which is involved in the electron transport chain, is located in the inner mitochondrial membrane, not the plasma membrane. This distinction is crucial because it underscores the specific roles of cellular membranes: the plasma membrane's role in cell signaling and permeability, compared to the inner mitochondrial membrane's role in energy production.