Final answer:
The major difference is that plasma contains clotting factors including fibrinogen, whereas serum is the component without these factors.
Step-by-step explanation:
The major difference between plasma and serum is that plasma contains the protein fibrinogen which is vital for blood clotting, whereas serum is the component of plasma that remains once these clotting factors have been removed. In essence, plasma without fibrinogen equals serum. Thus, option 1) Plasma contains the protein fibrinogen and serum does not, is correct.
Plasma, which makes up about 55% of blood by volume, contains other substances like hormones, antibodies, and electrolytes required for maintaining the body's physiological balance. On the other hand, serum includes elements such as antibodies and electrolytes but lacks the clotting factors present in plasma. Serum is commonly used in diagnostic tests due to the absence of clotting factors, while plasma can be used for blood transfusions as it contains these essential components.