Humber Admissions Practice Test

The plasma membrane forms the outer boundary of cells and is selectively permeable, meaning it regulates what enters and exits the cell. This characteristic is crucial for maintaining homeostasis within the cell, allowing essential substances such as nutrients and oxygen to enter while keeping out harmful substances. The structure of the plasma membrane, composed of a lipid bilayer with embedded proteins, enables it to interact with various molecules and respond to changes in the environment. Other options do not fulfill this role. The nuclear membrane surrounds the nucleus, protecting the genetic material but does not act as the outer boundary of the entire cell. The rough endoplasmic reticulum (ER) is involved in protein synthesis and processing but is an internal structure, not a boundary. The Golgi apparatus functions in modifying, sorting, and packaging proteins and lipids for secretion or use within the cell, again not serving as the cell's outer boundary. Thus, the plasma membrane is indeed the correct answer as it plays a vital role in the overall function and integrity of the cell.