Agglutination is the _______ of the ________

1. Analyze the question The question asks you to complete a definition of agglutination, a term from the topic of blood and blood groups.

2. Explain the concept Agglutination is the clumping together of red blood cells (erythrocytes). It happens when blood of incompatible groups is mixed.

• Red blood cells carry antigens (A and/or B) on their surface.
• Plasma contains antibodies (anti-A and/or anti-B).
• If an antigen meets its matching antibody (e.g. A antigen with anti-A antibody), the antibodies bind the cells and make them clump.

This is why blood transfusion must match blood groups. For example, giving group A blood to a group B person causes agglutination, which can block blood vessels and be fatal.

3. Step-by-step solution

• Option B ("coagulation of water"): water does not coagulate in this sense, so it is wrong.
• Option A ("coagulation of white blood cells"): agglutination does not involve white blood cells, so it is wrong.
• Option C ("white blood cells of red blood cell"): this makes no sense grammatically or biologically.
• Option D ("coagulation of the red blood cell"): this is the closest fit. The blank refers to the clumping (the question bank uses "coagulation" loosely for clumping) of red blood cells.

Strictly speaking, "coagulation" usually means blood clotting, which involves fibrinogen turning into fibrin. Agglutination is clumping of red cells caused by antigen-antibody reaction.

4. Answer D. coagulation, red blood cell

5. Exam tip Remember the difference:

• Agglutination = clumping of red blood cells (antigen-antibody reaction, blood groups).
• Coagulation = clotting of blood (platelets, fibrinogen → fibrin).

If you see "agglutination", think "red blood cells and blood groups". That alone will usually lead you to the right option.