What is the main function of leukocytes in the body?

Leukocytes, commonly known as white blood cells, play a crucial role in the immune system by defending the body against infections. Their primary function is to identify and eliminate pathogens such as bacteria, viruses, and other foreign invaders. This is achieved through various mechanisms, including engulfing and digesting these harmful organisms or producing antibodies that target specific pathogens.

The other choices, while important bodily functions, are not roles of leukocytes. For instance, energy production for cells is primarily handled by mitochondria within the cells themselves. Temperature regulation is managed by the hypothalamus and involves various body systems working together. The transport of oxygen is primarily the job of red blood cells, which contain hemoglobin to carry oxygen from the lungs to tissues throughout the body.