Final answer:
Phospholipids are the most abundant molecules in the plasma membrane, forming its essential bilayer structure and accounting for around 40 percent of its mass, followed by proteins and then a smaller amount of cholesterol and carbohydrates.
Step-by-step explanation:
The most abundant molecules in the plasma membrane are phospholipids, which form a bilayer that serves as the fundamental structure of the membrane. In a typical human cell, the plasma membrane is composed of approximately 50 percent proteins by mass, around 40 percent lipids (which includes phospholipids and cholesterol), and about 10 percent carbohydrates, primarily on the external surface of the membrane.
Phospholipids are crucial for the membrane's structure and integrity, while proteins play various functional roles such as transport, signal reception, and cell recognition. Cholesterol within the plasma membrane contributes to its fluidity and stability.