1. Phospholipids: These are the building blocks of the membrane, forming a bilayer. They have a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail. The hydrophilic heads face outwards, interacting with the watery environment both inside and outside the cell, while the hydrophobic tails face inwards, forming a barrier against the passage of water-soluble molecules.

2. Proteins: Embedded within the phospholipid bilayer are proteins that perform various functions, such as:

* Transport proteins: Facilitate the movement of specific molecules across the membrane.

* Receptor proteins: Bind to signaling molecules and initiate cellular responses.

* Enzymes: Catalyze biochemical reactions.

* Structural proteins: Provide support and shape to the membrane.

While phospholipids and proteins are the primary components, other molecules like cholesterol and carbohydrates can also be present in cell membranes, contributing to their structure and function.