What is the primary component of blood that contains white blood cells?

The primary component of blood that contains white blood cells is the formed elements. Formed elements refer to the cellular components of blood, which include red blood cells, white blood cells, and platelets. White blood cells, or leukocytes, play a critical role in the immune system by defending the body against infections and foreign substances.

Plasma, while being a key component of blood, primarily consists of water, electrolytes, proteins, and waste products, and does not contain cells. Platelets are involved in the blood clotting process and are also part of the formed elements, but they themselves do not contain white blood cells. Red blood cells, primarily responsible for transporting oxygen throughout the body, also do not contain white blood cells within their structure. Therefore, formed elements is the most accurate answer, as it encompasses all the cellular components of blood, including the crucial white blood cells.