Final answer:
Monocytes are converted into macrophages when they migrate from the blood into the tissues to search for foreign invaders. Macrophages phagocytize debris, foreign pathogens, and damaged cells, and release chemicals to attract other immune cells.
Step-by-step explanation:
Monocytes, which are a type of white blood cell, are converted into macrophages when they migrate from the blood into the tissues in search of foreign invaders in an animal host. Macrophages are responsible for phagocytizing debris, foreign pathogens, and damaged cells. They also release chemicals that attract other immune cells to the site of infection.