Main content of bilayer cell membrane is: March 2009
**Core Concept**
The main content of a bilayer cell membrane is a phospholipid bilayer composed of various lipids, proteins, and cholesterol. The phospholipid bilayer is the structural basis for cell membrane function, regulating the movement of substances in and out of the cell.
**Why the Correct Answer is Right**
The phospholipid bilayer is formed by the interaction of phospholipid molecules, which have a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail. This amphipathic nature allows the phospholipid molecules to arrange themselves in a bilayer structure, with the hydrophilic heads facing outwards and the hydrophobic tails facing inwards. This arrangement creates a fluid mosaic structure that is essential for cell membrane function.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option would be incorrect because it doesn't specify the type of substance that makes up the cell membrane.
* **Option B:** This option is incorrect because the cell membrane is not primarily composed of proteins, although proteins are embedded within the phospholipid bilayer.
* **Option C:** This option is incorrect because while cholesterol is an important component of the cell membrane, it is not the main content of the bilayer.
**Clinical Pearl / High-Yield Fact**
The phospholipid bilayer is essential for cell membrane function, and disruptions to this structure can lead to various diseases, including certain types of cancer and neurodegenerative disorders.
**Correct Answer:** **B.** Phospholipids.