AP BIOLOGY

Detailed explanation-1: -Being cylindrical, phospholipid molecules spontaneously form bilayers in aqueous environments. In this energetically most-favorable arrangement, the hydrophilic heads face the water at each surface of the bilayer, and the hydrophobic tails are shielded from the water in the interior.

Detailed explanation-2: -Because their fatty acid tails are poorly soluble in water, phospholipids spontaneously form bilayers in aqueous solutions, with the hydrophobic tails buried in the interior of the membrane and the polar head groups exposed on both sides, in contact with water (Figure 2.45).

Detailed explanation-3: -Following the rule of “like dissolves like", the hydrophilic head of the phospholipid molecule dissolves readily in water. The long fatty acid chains of a phospholipid are nonpolar, and thus avoid water because of their insolubility.

Detailed explanation-4: -The fatty acid tails can easily interact with other nonpolar molecules, but they interact poorly with water. Because of this, it’s more energetically favorable for the phospholipids to tuck their fatty acid tails away in the interior of the membrane, where they are shielded from the surrounding water.

Detailed explanation-5: -Phospholipids spontaneously assemble into specific lipid structures because of the tendency of polar molecules like water to exclude non polar molecules or groups within molecules. Specific shape is determined by bulkiness of the head group relative to that of the hydrophobic tails.