The correct answer is D. Biological membranes are composed of phospholipids, proteins, and carbohydrate groups.
Phospholipids are a type of lipid that are amphipathic, meaning that they have both a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail. This allows them to form a bilayer structure, with the hydrophobic tails facing each other in the middle of the membrane and the hydrophilic heads facing the water on either side.
Proteins are another important component of biological membranes. They can be found embedded in the lipid bilayer, or they can be attached to the surface of the membrane. Proteins have a variety of functions in membranes, including transport, signaling, and cell adhesion.
Carbohydrate groups are also found on the surface of biological membranes. They can be attached to proteins or lipids, and they help to identify and interact with other cells.
Together, phospholipids, proteins, and carbohydrate groups form a complex and dynamic structure that is essential for the function of cells.