Final answer:
Microfilaments are polar due to their directional assembly of actin monomers, interacting with motor proteins like myosin, while keratin intermediate filaments are non-polar structures designed for tensile strength.
Step-by-step explanation:
Microfilaments are polar because they are made up of actin monomers that assemble in a specific orientation, where the plus-end is different from the minus-end, allowing for directional growth and interaction with motor proteins like myosin. This polarity is crucial in processes such as cell motility and muscle contraction. In contrast, keratin filaments, which are a type of intermediate filaments, do not have this polarity. They are made up of coiled dimers that assemble into tetramers, which then form a non-polar structure. The lack of polarity in keratin filaments is because they are designed for tensile strength, forming rope-like structures that resist pulling forces and do not need to interact with motor proteins in the same way as microfilaments.