Final answer:
The lipid bilayer acts as a barrier, while proteins, including integral and peripheral proteins, provide specific transport and recognition functions. Carbohydrates contribute to cell recognition and adhesion, and cholesterol enhances membrane flexibility.
Step-by-step explanation:
The lipid bilayer serves as a barrier to most water-soluble molecules, while the proteins carry out other functions and give the membrane its individual characteristics. The phospholipid bilayer is a fundamental component of cell membranes, providing selective permeability due to its hydrophobic interior that prevents passage of many substances. However, integral proteins are embedded in the bilayer, forming channels for selective transport of molecules that cannot pass through the lipid barrier alone. Additionally, carbohydrates attached to the proteins and lipids contribute to cell recognition and adhesion processes, cholesterol adds flexibility to the membrane, and peripheral proteins are also involved in the cell's recognition sites. These elements work together to maintain the unique function and integrity of the cell membrane.