This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: membrane structure and function, Subject name: Biochemistry
The major driving force for formation of membrane lipid bilayer is 
Select and explain. 
A. Hydrogen bonding, B. Hydrophobic interactions, C. Van der waal forces, D. Not known
B: Hydrophobic interactions
Answer: B: Hydrophobic interactions 
Explanation: The molecules align themselves to form monolayers with the polar heads pointing in one direction and the nonpolar tails in the opposite direction (Figs 7.7A and B). Only fatty acids with more than 6 carbon atoms form monolayers. This explains their role as components of biomembranes The self-assembly of phospholipids into bilayers is driven by hydrophobic interaction. They also act as detergents and emulsifying agents. In vivo, they act as pulmonary surfactants.Ref: DM Vasudevan, page no: 79