In electrophoresis, what term describes the movement of buffer ions and solvents within the support material?

• A. Endosmosis
• B. Iontophoresis
• C. Zone electrophoresis
• D. Isoelectric focusing

Answer: (A)

The main idea tested here is the bulk flow of liquid through a gel under an electric field, known as endosmosis (often called electroendosmosis in electrophoresis). When voltage is applied to a gel, the gel has fixed charges that interact with the surrounding buffer. The mobile counterions in the gel’s diffuse layer are dragged toward the opposite electrode, and because they pull water with them, there is a net flow of buffer solution through the gel. This solvent movement can influence how all components migrate, sometimes altering band positions or broadening bands.

That’s why this option is the best description: it captures the solvent and ion movement inside the support material caused by the electric field. The other terms describe different phenomena—driving ions into tissues (not the gel’s solvent flow), separating species along a continuous zone, or focusing proteins in a pH gradient—so they don’t describe the solvent movement in the gel.