Final answer:
Cell crawling depends on actin polymerization, the assembly of actin monomers into microfilaments. Microtubule assembly and hydrolysis of ADP by motor proteins do not directly contribute to cell crawling. Intermediate filaments provide structural support but are not involved in cell motility.
Step-by-step explanation:
Cell crawling depends on actin polymerization, which is the assembly of actin monomers into microfilaments. Actin, a protein found in cells, has a dynamic nature that allows it to polymerize and depolymerize, making it essential for cellular processes such as cell movement and shape change. Microtubules, another component of the cytoskeleton, play a role in intracellular movement but are not directly involved in cell crawling. They act as tracks for motor proteins that transport vesicles and pull replicated chromosomes during cell division. Intermediate filaments provide structural support to the cell but do not play a role in cell motility.
Therefore, the correct answer to the question is option A: actin polymerization.