Why does the phospholipid bilayer form the way it does in biological membranes?

• A. Because phospholipids are soluble in water
• B. Because phospholipids have hydrophilic heads and hydrophobic tails
• C. Because phospholipids are hydrophobic and repel water
• D. Because phospholipids are attracted to each other by ionic bonds

Answer: (B)

Verified step by step guidance

1. Understand the structure of phospholipids: Phospholipids consist of a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails. The head is typically composed of a phosphate group, while the tails are long fatty acid chains.
2. Recognize the behavior of phospholipids in water: When placed in an aqueous environment, the hydrophilic heads of phospholipids are attracted to water, while the hydrophobic tails avoid water. This dual nature is crucial for the formation of the bilayer.
3. Explain the formation of the bilayer: In biological membranes, phospholipids arrange themselves into a bilayer with the hydrophilic heads facing outward towards the water on both sides, and the hydrophobic tails facing inward, away from the water. This arrangement minimizes the exposure of the hydrophobic tails to water.
4. Discuss the stability of the bilayer: The phospholipid bilayer is stable because the hydrophilic heads interact with the aqueous environment, while the hydrophobic tails interact with each other, creating a barrier that is selectively permeable to certain substances.
5. Clarify misconceptions: Phospholipids do not form the bilayer due to ionic bonds or because they are soluble in water. The key factor is the amphipathic nature of phospholipids, which drives the self-assembly into a bilayer structure.