Question

Thickness of plasma membrane is
A) 10A° to 30A°
B) 30A° to 50A°
C) 50A° to 70A°
D) 70A° to 100A°

Answer 1

The plasma membrane, also called cell membrane, separates the interior of the cell from the outside environment. The cell is enclosed by this barrier that allows the entry of only a few molecules.

Complete answer:
In bacteria and plants, a cell wall is present outside of the plasma membrane. It is a semipermeable membrane that regulates the transport of materials into and outside the cell. Plasma membrane has various functions like, it provides protection to the cell, transport of nutrients into the cell and toxic substances outside the cell. Due to the high $K^+$ ion inside the cell, the membrane potential is -20mV. It is made up of lipid, protein, and carbohydrates.
The main components of the cell membrane are the phospholipids, the outermost layer of cells. It is amphiphilic in nature i.e. contains both polar and nonpolar heads. The polar head (hydrophilic) contains the phosphate group and the two nonpolar tails (hydrophobic) are hydrocarbons. One tail is unsaturated (one or more double bonds) while the other is saturated, affecting the packaging and fluidity of the membrane. The spontaneous arrangement of the phospholipids form the lipid bilayers.
The proteins make up the second major components of the plasma membrane. There are two types: integral proteins, which span the membrane and interact with the hydrophobic region of the phospholipid layer, and peripheral proteins, found on the exterior surface temporarily associated with the membranes.
Carbohydrates are the third major component of plasma membrane and are found on the exterior surface of the cell. It consists of 2-60 monosaccharide units.
Cholesterol molecules are randomly distributed across the phospholipid bilayer. It helps the bilayer to stay fluid in different environmental conditions.
With all these layers, the thickness of the plasma membrane ranges from 7 to 10nm or 70A° to 100A°.

Hence the correct answer isn option ‘D’.

Note: In 1972, S. J. Singer and G. L. Nicolson proposed the fluid mosaic model. According to this, the biological membranes can be considered as a two-dimensional liquid in which lipid and protein molecules diffuse easily.The combination of lipids and proteins gives the cell membrane their distinctive permeability qualities.