**Question:** Phagocytosis enhanced by coating the surface of antigen is called -

A. Opsonization
B. Phagocytosis
C. Phagocytosis
D. Agglutination

**Correct Answer:** A. Opsonization

**Core Concept:**
Phagocytosis is a cellular process where immune cells, such as macrophages and neutrophils, engulf and destroy pathogens and cellular debris by engulfing them within their plasma membrane. Opsonization is a crucial mechanism that enhances phagocytosis by coating the surface of antigens (pathogens or foreign particles) with specific proteins, such as complement proteins (e.g., C3b), which facilitates the recognition and engulfment of the antigen by phagocytic cells.

**Why the Correct Answer is Right:**
Opsonization is essential for enhancing phagocytosis because it:
1. Increases the binding affinity between the antigen and phagocytic cells through complement proteins (e.g., C3b) acting as opsonins.
2. Activates the phagocytic cells to recognize and engulf the opsonized antigen.
3. Promotes the fusion of the phagocytic membrane with the engulfed antigen, thus facilitating the internalization process.

**Why Each Wrong Option is Incorrect:**
1. **Option B (Phagocytosis):** This term refers to the process of engulfment itself, not the process that enhances it.
2. **Option C (Phagocytosis):** Similar to Option B, it describes the process, not the mechanism that enhances it.
3. **Option D (Agglutination):** Agglutination is the process of particle aggregation due to specific antibodies or other proteins, which is unrelated to the process of enhancing phagocytosis.

**Clinical Pearl:**
Opsonization is crucial for the efficient clearance of pathogens and foreign particles by the immune system, particularly in the context of bacterial infections. Recognizing and targeting opsonized bacteria, for instance, enhances the efficiency of phagocytes in engulfing and destroying the pathogens, thus playing a vital role in the defense mechanisms of the human body.