Final answer:
An integral protein, often termed a transmembrane protein when it spans across the entire membrane, is a protein that spans one layer of the lipid bilayer and is a critical component of cellular membranes.
Step-by-step explanation:
The name given to a protein which spans one layer of the bilayer is an integral protein. These proteins are essential components of cellular membranes, and their structure is such that they have both hydrophobic and hydrophilic regions. The hydrophobic regions interact with the hydrophobic interior of the phospholipid bilayer, allowing the protein to integrate completely into the membrane structure. On the other hand, their hydrophilic regions protrude from the membrane and enable interaction with the surrounding intracellular or extracellular environment. An example of such a protein is a transmembrane protein, which can span the entire membrane and be exposed on both sides. Some integral proteins are single-pass, meaning they only traverse the membrane once, while others can span the membrane multiple times and may form complex structures with up to 12 segments.