Question

Which chemical property is shared by all types of lipids forming the plasma membrane?
A. Sugar component
B. Glycerol backbone
C. Phosphate group
D. Hydrophobic region

Answer 1

Hint: Plasma membranes are double-layered structures that surround the cells or organelles. They provide protection to inner contents and hold them in place and shape. All of the membranes are usually made of proteins and lipids. The lipids are amphipathic in nature.

Complete answer:
The plasma membrane forms the covering of cells and other internal cellular organelles. It is the outermost envelope-like membrane. It is a double membranous structure. It is also called a phospholipid bilayer and is found in all of the prokaryotes and eukaryotes. The plasma membrane functions as a boundary that selectively permeates the entry and exit of selective molecules. Also, the plasma membrane keeps the cell in shape and connected to its environment.

The plasma membrane is made up of phospholipids and proteins mainly carbohydrates. Other conjugate molecules are also found in some plasma membranes. A typical membrane is 5 to 8 nanometer thick. The cytoplasm of a cell is enclosed inside the flexible lipid bilayer. The fluid mosaic model given by Garth L. Nicolson and Seymour Jonathan Singer explains the details of the structure of the plasma membrane. According to this model, the amphipathic lipids have a hydrophilic head that points outside and a hydrophobic tail that points inside. Two layers of lipids form a lipid bilayer. The proteins stay embedded in the bilayer along with other molecules. This gives the membrane a mosaic look. All of the membranes have lipid bilayer and proteins embedded in them as basic structural components. The hydrophobic tails of lipids do not allow water to enter the bilayer directly.
Thus, the right answer is option D.

Note: Aquaporins are specialized protein channels that allow water to enter the bilayer and reach the cell. As the hydrophobic tails of lipids do not allow water to pass it is a slow and passive process. Also, to provide minimum resistance to water passage the tails of lipids face each other inwardly.