Multiple choice Which of the following is a major constituents of cell membranes? Phosphatidylcholines Phosphatidylinositol Phosphatidylethanolamine Phosphatidic acids Reveal answer Fill a bubble to check yourself D Correct answer Explanation Phosphatidic acids (PAs) are the acid forms of phosphatidates, a part of common phospholipids, major constituents of cell membranes. Phosphatidic acids are the simplest diacyl-glycerophospholipids.