What component of blood primarily transports everything except oxygen?

Plasma is the component of blood that primarily transports a variety of substances throughout the body, excluding oxygen. It is a yellowish fluid that makes up about 55% of total blood volume and is composed mostly of water, with dissolved proteins, ions, nutrients, hormones, and waste products. Plasma serves as the medium through which these components are transported, ensuring that essential substances are delivered to cells and that metabolic waste is carried away for excretion.

In contrast, red blood cells are specialized for the transport of oxygen and carbon dioxide due to the presence of hemoglobin, while leukocytes are primarily involved in immune responses, and platelets play a critical role in blood clotting. Therefore, plasma is uniquely positioned as the transporter of materials other than gases like oxygen, making it the correct answer.