Question

which protein filament forms the membrane skeleton to support the plasma membrane?
cytoskeleton
intermediate filament
microfilament
microtubules

Explanation:

The membrane skeleton that supports the plasma membrane is formed by spectrin - based filaments which are part of the intermediate filament - related network. Intermediate filaments provide mechanical strength and support to the plasma membrane. Cytoskeleton is a general term for the network of protein filaments in the cell. Microfilaments are mainly involved in cell movement and shape changes. Microtubules are important for cell division and intracellular transport.

Answer:

Intermediate filament