What is the primary function of white blood cells in the body?

White blood cells, also known as leukocytes, play a crucial role in the immune system, and their primary function is to defend the body against infections and disease. They achieve this by identifying and destroying pathogens, such as bacteria and viruses, that can cause illness. This immune response involves various types of white blood cells, including phagocytes, which engulf and digest these foreign invaders, and lymphocytes, which can identify and remember specific pathogens for more effective elimination if they invade again.

This protective function is essential for maintaining overall health and resilience against infectious diseases, making it fundamental to the body's ability to survive and thrive despite constant exposure to harmful microorganisms. In contrast, the other options pertain to different bodily functions: transporting oxygen is the role of red blood cells, hormone production is primarily managed by glands in the endocrine system, and energy generation for muscle movement is facilitated by processes involving muscle fibers and ATP (adenosine triphosphate) rather than white blood cells.