The cellular process by which white blood cells migrate toward higher concentrations of a chemical signal is called?

• A. Phagocytosis
• B. Endocytosis
• C. Pinocytosis
• D. Chemotaxis

Answer: (D)

When a cell moves toward higher concentrations of a chemical signal, the cell is performing chemotaxis. White blood cells read chemical gradients—like chemokines released at infection or injury sites—and orient their movement accordingly. They detect the signal with surface receptors, triggering intracellular signals that reorganize the actin cytoskeleton so the cell extends a leading edge (pseudopod) in the direction of the gradient and drags the rest of the cell forward. This directed migration is what brings immune cells to the exact location where they’re needed.

By contrast, phagocytosis is the process of engulfing and internalizing particles after contact, endocytosis is the general uptake of material into the cell via vesicles, and pinocytosis is uptake of extracellular fluid. These actions describe intake, not the directional movement toward a chemical cue.