Which description correctly states roles of phospholipids and cholesterol in cell membranes?

• A. Phospholipids form a bilayer that creates a semi-permeable barrier; cholesterol intercalates in the bilayer modulating fluidity and serves as precursor for steroid molecules like vitamin D and sex hormones.
• B. Phospholipids dissolve membrane proteins to allow free diffusion of ions, and cholesterol is the main transporter of fat-soluble vitamins in the bloodstream but not a membrane component.
• C. Phospholipids produce ATP in the membrane while cholesterol acts exclusively as a storage form of carbohydrate and is not involved in hormone precursor pathways.
• D. Cholesterol forms the outermost carbohydrate coat of the membrane, and phospholipids are only involved in intracellular signaling unrelated to membrane structure.

Answer: (A)