Detailed Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Problem:Passage: The dual character is critical for the formation of the lipid bilayer. The hydrophilic portions of the molecule are in contact with the aqueous environment of the cell, while the hydrophobic portion of the lipids is in the interior of the bilayer and provides a barrier to the passive diffusion of most molecules. Answer: lipid bilayer
Solution:
The dual character is critical for the formation of the what?