Final answer:
The cell membrane is composed of (Option b) two layers of lipids, specifically phospholipids, with embedded cholesterol molecules providing structural support.
Step-by-step explanation:
The cell membrane is composed of two layers of lipids, making the correct answer to the question (b) 2. These lipid layers are primarily made up of molecules called phospholipids, which have a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) fatty acid tails. This structure creates a bilayer with the hydrophilic heads facing the aqueous environment inside and outside the cell, while the hydrophobic tails face each other in the middle, creating a semi-permeable barrier that regulates what enters and exits the cell.
Additionally, cholesterol is an important component of the cell membrane, providing rigidity and fluidity to the membrane. Cholesterol molecules are embedded within the phospholipid bilayer.