Which component of blood is primarily responsible for transporting oxygen?

Erythrocytes, also known as red blood cells, are primarily responsible for transporting oxygen throughout the body. They contain a special protein called hemoglobin, which binds to oxygen molecules in the lungs and releases them in the tissues where they are needed. The structure of erythrocytes is also specialized for this function; they have a biconcave shape that increases their surface area, enhancing their ability to absorb and release oxygen efficiently.

In contrast, leukocytes, or white blood cells, are part of the immune system and play a role in defending the body against infections but do not transport oxygen. Platelets are involved in blood clotting and preventing bleeding but are not involved in oxygen transport. Plasma is the liquid component of blood that helps transport various substances, including nutrients and waste, but it does not carry oxygen in the same direct manner as erythrocytes do. This makes erythrocytes the correct choice for the component primarily responsible for oxygen transport in the bloodstream.