Final answer:
The protein molecule found for every 50-100 phospholipids in a cell membrane, typically spanning the membrane and involved in various functions is the integral or transmembrane protein.
Step-by-step explanation:
For every 50-100 phospholipids in the membrane, there is typically one protein molecule, and while there are several types of proteins associated with the cell membrane, the protein that is often embedded within the membrane, serving various functions such as acting as channels or pumps, is known as the integral protein. Also referred to as transmembrane proteins, integral proteins span the entire phospholipid bilayer with hydrophobic and hydrophilic domains that interact with the membrane's environment. This integration allows them to move materials in and out of the cell, participate in cell recognition, and help maintain cellular structure. In contrast, peripheral proteins are more loosely associated and bind to the membrane surface or to integral proteins without spanning the bilayer.
When considering the specific ratio of phospholipids to protein molecules in the membrane and the types of proteins that could be implied, the correct answer is an integral protein or a transmembrane protein. This choice is supported by the provided references, which discuss the various roles and structural positioning of integral proteins within the cell membrane.