Intermediate filaments are described as

• A. Threadlike proteins roughly twice as thick as microfilaments
• B. The primary energy producers of the cell
• C. The sites of protein synthesis
• D. The backbone of cell membranes

Answer: (A)

Intermediate filaments are part of the cytoskeleton that provide mechanical strength and resilience to cells. They form threadlike fibers that are thicker than microfilaments but thinner than microtubules, giving them a rope‑like quality. This size and structure help them stabilize cell shape, anchor organelles, and support the nuclear envelope. They are not energy producers, not sites of protein synthesis, and not the architectural backbone of the membrane. Describing them as threadlike proteins roughly thicker than microfilaments best matches their role and size relative to other cytoskeletal elements.