Final answer:
The step in phagocytosis where phagocytes adhere to microbes, often requiring opsonization, is known as recognition and adherence.
Step-by-step explanation:
During the process of phagocytosis, the step that involves receptors on phagocytes adhering to microbes, which may require opsonization for effective binding, is called recognition and adherence. Opsonization is the coating of the pathogen with molecules, such as complement factors or antibodies like IgG, to assist in phagocyte binding and facilitate phagocytosis. Phagocytic cells, such as macrophages, dendritic cells, and neutrophils, have receptors on their surface that recognize and bind to the Fc portion of the IgG molecules; this helps the phagocyte attach to and engulf the pathogens they have bound. Furthermore, opsonins can mark the antigen for phagocytosis by neutrophils, while proteins like clathrin can stabilize the inward-facing surface of the plasma membrane during the process.