In the fluid-mosaic model of the plasma membrane, the phospholipid molecules are oriented so that the heads are facing the outside environment and the tails are facing the interior of the membrane.

Hydrophilic heads facing exterior

Hydrophobic tails facing interior

Explanation:

In 1972, the fluid mosaic model was proposed to describe the structure of the plasma membrane. This model describes the plasma membrane to possess components including phospholipids, cholesterol and proteins. The phospholipid component is composed of glycerol, two fatty acids and a phosphate-containing head, which are arranged in two adjacent layers forming the phospholipid bilayer in the membrane of biological organisms.

Phospholipids have both the hydrophilic and hydrophobic region. Hence they are said to be AMPHIPATHIC.

The head of the phospholipid is negatively charged due to its phosphate content, making it polar and hydrophilic i.e. water-loving. This hydrophilic head faces the exterior of the cell in order to interact with fluids.

The tails of the phospholipid are long fatty acids that keep away from water i.e. hydrophobic. Due to their water-fearing nature, they avoid water and face the interior of the cell, where each tail face each other.

oceans

indian ocean

pacific ocean

atlantic ocean

arctic ocean

southern ocean

the darker peppered moth species were favored due to the fact that the industrial revolution had made all the nearby trees a darker color instead of white.