Phospholipids make up most of the lipid part of the cell membrane. since water exists on both the outside and inside of a cell, which of the following phospholipid arrangements makes the most sense?
a. a single layer of phospholipids with the polar heads facing outside the cell
b. two back-to-back phospholipid layers with the non-polar tails facing out on both sides
c. a single layer of phospholipids with the polar heads facing inside the cell
d. two back-to-back phospholipid layers with the polar heads facing out on both sides

The correct option is D. (Two back-to-back phospholipid layers with the polar heads facing out on both sides)

Explanation:

The plasma membrane creates a barrier between the interior part of the cell and the cytoplasm. It is consisting of proteins and phospholipids and bi-layered in nature. Phospholipids are known as the main component of the plasma membrane.

Phospholipids are composed of alcohol and fatty acids and they are arranged in a specific manner. Each phospholipid molecule contains a water-hating tail that is hydrophobic in nature and a water-loving head which is hydrophilic in nature and the polar heads face the outside.