Final answer:
Integral proteins are the most abundant proteins in the membrane. Some protrude from one side of the membrane and act as receptors, providing attachment sites for extracellular molecules and activating intracellular response cascades.
Step-by-step explanation:
The most abundant protein in the membrane are integral proteins. They are embedded in the lipid bilayer and can span the entire plasma membrane. Some integral proteins can protrude from one side of the membrane, acting as receptors. These receptors provide attachment sites for extracellular molecules and activate intracellular response cascades when their effectors are bound.