Approximately what percentage of blood is made up of plasma?

Plasma constitutes about 55% of the total blood volume in humans. This yellowish fluid plays a crucial role in maintaining blood pressure and regulating body temperature. It serves as the medium for transporting essential components such as nutrients, hormones, and waste products throughout the body. Additionally, plasma is vital for the proper functioning of the immune system and contains proteins that contribute to blood clotting and other vital processes.

In contrast, the other percentages presented do not accurately reflect plasma's proportion in blood. While some components of blood such as red blood cells account for approximately 45%, which might lead to confusion, the correct proportion of plasma is indeed vital to understand its crucial functions in the circulatory system. Thus, the answer providing that plasma comprises 55% of blood is the most accurate and reflects standard physiological understanding.