Question

Which best describes the arrangement of phospholipids in a phospholipid bilayer like that found in a cell membrane?

• A. Two layers of phospholipids where the outer layer has the hydrophobic tails facing toward the outside of the cell and the inner layer have the hydrophobic tails facing toward the inside of the cell.
• B. Two layers of phospholipids where the outer layer has the hydrophilic heads facing toward the outside of the cell and the inner layer have the hydrophilic heads facing toward the inside of the cell.
• C. Two layers of phospholipids where the outer layer has the hydrophilic heads facing toward the outside of the cell and the inner layer have the hydrophobic tails facing toward the inside of the cell.
• D. Two layers of phospholipids where the two layers have alternating components such that one pair of components across the membrane are arranged head to tail and the pair adjacent to it are arranged head to tail in the opposite direction.
• E. A single layer of phospholipids where the hydrophilic head is facing toward the outside of the cell and the hydrophilic tail is facing toward the inside of the cell.

Answer 1

The correct option is C Two layers of phospholipids where the outer layer has the hydrophilic heads facing toward the outside of the cell and the inner layer have the hydrophobic tails facing toward the inside of the cell.

There are various models proposed to explain the structure of cell membrane. The most accepted model is Fluid-Mosaic model proposed by Singer and Nicholson. According to fluid mosaic model, cell membrane is 7 nm thick with phospholipid layer as the basic layer. There are two phospholipid layers. The hydrophilic phosphate heads of phospholipids face outward from both the sides into the aqueous environment. The hydrocarbon tails i.e. hydrophobic tails face inward and create a hydrophobic interior.

So, the correct answer is 'Two layers of phospholipids where the outer layer has the hydrophilic heads facing toward the outside of the cell and the inner layer have the hydrophobic tails facing toward the inside of the cell.'.