Humber Admissions Practice Test 2026 - Free Practice Questions and Study Guide for Humber College Admissions

The plasma membrane is best described as a phospholipid bilayer. This structure is fundamental to the function of the membrane, as it consists of two layers of phospholipids arranged tail-to-tail. The hydrophobic (water-fearing) tails face inward, away from water, while the hydrophilic (water-attracting) heads face outward towards the intracellular and extracellular fluids. This arrangement allows the plasma membrane to form a barrier that separates the internal environment of the cell from the outside environment while still being semi-permeable, meaning it can regulate which substances enter and leave the cell.

The phospholipid bilayer is crucial for various cellular functions such as protecting the cell, facilitating communication with other cells, and enabling the transport of materials in and out of the cell. Furthermore, it interacts with various proteins and cholesterol, which are embedded within or associated with it, providing additional functionality and stability.

In contrast, the terms used in the other options do not accurately describe the plasma membrane in the same fundamental way. While membranes may be part of the endoplasmic reticulum, a simple layer does not capture the complexity or structure of the plasma membrane, and calling it a complex structure is overly general without specifying the bilayer nature essential to