Question

which macromolecule forms a double layer as the primary structure of cell membranes?
○ fats
○ oils
○ phospholipids
○ steroids

Explanation:

To determine the macromolecule forming the cell membrane's double - layer structure, we analyze each option:

• Fats: They are mainly for energy storage and insulation, not the cell membrane's primary structure.
• Oils: Similar to fats, they are used for energy storage and do not form the cell membrane's double layer.
• Phospholipids: They have a hydrophilic head and hydrophobic tails. In an aqueous environment (like the inside and outside of a cell), they spontaneously arrange into a bilayer. The hydrophilic heads face the water - containing regions (inside and outside the cell), and the hydrophobic tails face each other, forming the basic structure of the cell membrane.
• Steroids: They are a type of lipid, but their main functions are related to signaling (like hormones) or adding rigidity to the membrane, not forming the primary double - layer structure.

Answer:

C. phospholipids