What is the primary structural role of sterols (like cholesterol or ergosterol) in eukaryotic plasma membranes?

Sterols modulate membrane fluidity and stability, preventing membranes from becoming too rigid or too permeable, and thereby maintain proper membrane function.

Sterols serve as the main energy-storage molecules in the plasma membrane and are metabolized during cellular respiration to power membrane transport processes.

Sterols act as primary cell-surface antigens that are recognized by innate immune receptors, providing the cell with immunological identity.

Sterols are the exclusive anchoring sites for cytoskeletal microtubules on the inner membrane surface, directly controlling mitotic spindle assembly through membrane-bound receptors.