If a small droplet of triacylglycerol molecules is suspended in water, the fat molecules form a "ball of spaghetti" with no particular orientation. But if a droplet of phospholipid molecules is put in water, all the molecules point outward, toward the water. Phospholipids are forced into this orientation because phospholipids have __________.

• A. three fatty acid molecules, all pointing in different directions
• B. two fatty acid molecules pointing in different directions
• C. both a saturated fatty acid and an unsaturated fatty acid
• D. two charged or polar ends
• E. a charged or polar end and an uncharged or nonpolar end

Answer: (E)

Verified step by step guidance

1. Understand the structure of triacylglycerol molecules: Triacylglycerols are composed of three fatty acid chains attached to a glycerol backbone. These molecules are nonpolar and hydrophobic, meaning they do not interact favorably with water.
2. Recognize the structure of phospholipid molecules: Phospholipids consist of a glycerol backbone, two fatty acid tails, and a phosphate group attached to a polar head. This structure gives phospholipids both hydrophobic (nonpolar) and hydrophilic (polar) properties.
3. Identify the behavior of triacylglycerols in water: Due to their nonpolar nature, triacylglycerols do not have a specific orientation in water and tend to clump together in a disordered manner, like a 'ball of spaghetti.'
4. Analyze the behavior of phospholipids in water: The polar head of phospholipids is hydrophilic and interacts with water, while the nonpolar tails are hydrophobic and avoid water. This dual nature forces phospholipids to orient themselves with the polar heads facing outward towards the water and the nonpolar tails facing inward, away from the water.
5. Conclude why phospholipids form a specific orientation: The presence of both a charged or polar end (the phosphate group) and an uncharged or nonpolar end (the fatty acid tails) in phospholipids causes them to align in a specific manner in aqueous environments, unlike triacylglycerols.