Final answer:
Collagen is the single most abundant protein in the body, present in several connective tissues and making up about 30% to 35% of vertebrate proteins by weight.
Step-by-step explanation:
The single most abundant protein in the body is collagen. Collagen is a structural protein that forms a triple helix, giving it strength and elasticity, which is crucial in various connective tissues including tendon, cartilage, blood vessels, skin, and bone. It constitutes approximately 30% to 35% of the protein mass of vertebrates, making it more prevalent than other proteins such as hemoglobin, which is a globular protein responsible for oxygen transportation in the blood, or albumin, which is the most abundant protein in human blood plasma. While hemoglobin, albumin, and immunoglobulins play vital roles in physiological functions like transport of oxygen and CO2, regulation of osmotic pressure, and immune response respectively, they do not surpass the abundance of collagen in the body.