Which cytoskeletal element helps determine cell shape during phagocytosis?

The correct answer is actin filaments. During phagocytosis, a process through which cells engulf large particles, actin filaments play a crucial role in determining cell shape and enabling the extension of the cell membrane to surround and internalize the particle.

Actin filaments are dynamic structures that can rapidly assemble and disassemble, which allows the cell to alter its shape efficiently. In phagocytosis, actin polymerization supports the formation of pseudopodia—protrusions that extend out from the cell body. These pseudopodia are key for the engulfment of the particles, as they wrap around and subsequently encapsulate the object to form a phagosome.

While microtubules and intermediate filaments are important for maintaining cellular structure and providing rigidity or mechanical support, they do not play a direct role in the morphological changes necessary for phagocytosis. Collagen fibers are part of the extracellular matrix and contribute to tissue structure but are not involved in the dynamic process of phagocytosis within the cell. Hence, they do not influence the determination of cell shape during this process.