What is the function of white blood cells?

White blood cells, or leukocytes, play a crucial role in the immune system by defending the body against infection and disease. They are essential components that help identify and destroy pathogens, such as bacteria, viruses, and other foreign invaders. Different types of white blood cells have specialized functions; for instance, some can directly attack and destroy pathogens, while others produce antibodies that target specific invaders.

While other choices describe important functions within the circulatory and clotting systems, they do not pertain to the primary role of white blood cells. For example, the transportation of oxygen is the responsibility of red blood cells, and blood clotting primarily involves platelets and clotting factors. Hence, the choice highlighting the defense function of white blood cells accurately reflects the primary and vital role they play in maintaining health and fighting infections.