Final answer:
Carbohydrates on the exterior of cell membranes primarily facilitate cell recognition, allowing the immune system to differentiate between self and non-self entities, which is central to immune responses.
Step-by-step explanation:
The primary function of carbohydrates attached to the exterior of cell membranes is to facilitate cell recognition. These carbohydrates are bound to proteins, forming glycoproteins, or to lipids, forming glycolipids. Together, they constitute the glycocalyx, which plays a crucial role in enabling the immune system to distinguish between the body's own cells (self) and foreign cells or tissues (non-self). These carbohydrate chains are composed of 2-60 monosaccharide units and can be straight or branched, forming unique patterns on the cell surface similar to facial features that allow for individual recognition. The recognition function is pivotal for the immune system's response to pathogens, as it identifies and targets foreign invaders.
In addition to recognition, these carbohydrates contribute to cell adhesion and interact with the watery environment, aiding in the cellular interactions that are crucial for various physiological processes.