Question

What is the size of molecules which can pass through the plasma membrane?
A. 4-15 angstrom
B. 25-80 angstrom
C. 8-10 angstrom
D. 10-35 angstrom

Answer 1

Hint:-Plasma membrane is composed of protein, lipids, and carbohydrate molecules. The plasma membrane is responsible for enclosing the cell and cellular organelles. It separates the cells from the outer environment and cellular organelles from the cytoplasm within the cell. Plasma membrane allows the transportation of some specific molecules.

Complete answer:
The plasma membrane is also known as the cell membrane. The plasma membrane comprises a trilaminar structure that involves the parallel arrangement of outer protein layers and the inner phospholipid layer. The outer protein layer is osmophilic and the inner lipid layer is osmophobic. In the core region, the phosphate group (hydrophilic) of the phospholipids occupy the surface area and the inner fatty acid chain (hydrophobic) remains inside the membrane. This unique arrangement of the lipid layer makes the cell membrane selectively permeable.
The total thickness of the plasma membrane is 75 angstrom within which the phospholipid layer comprises a thickness of 35 angstrom and a protein layer possesses a thickness of 20 angstrom. Only some specific substances which are unchanged can pass through the lipid bilayer of the plasma membrane by the diffusion process. The particles which can transport through the plasma membrane or cell membrane comprises the size of 4-15 angstrom. The molecules having a size greater than 15 angstrom are not allowed to pass through the cell membrane.

Additional information:
Diffusion: When the solute of a solution moves from the higher concentration to lower concentration is called diffusion. There are two types of diffusions that are noticed. These are simple diffusion and facilitated diffusion.

So, the correct answer is option A. 4-15 angstrom.

Note:- The capacity of the plasma membrane which involves the transport of selective molecules and prevents other particles (polar molecules) passage is known as selective permeability. The molecules which can pass through the cell membrane are water, oxygen, carbon dioxide, small lipid molecules, vitamins which are soluble in fat, hormones, etc.