Question

How is concentration gradient related to the process of diffusion?

Answer 1

Hint: Diffusion is a process used for the movement of substances in and out of a cell depending upon their concentration gradients. It is a passive process.

Complete answer:
The net movement of particles or substances from a region of its higher concentration to a region of its lower concentration without the expenditure of ATP or energy is known as Diffusion. The diffusion of substance completely depends on the concentration gradient between the two areas. Concentration is the amount of substance present in a given volume or total volume. Its SI unit is mol/liter. A concentration gradient is developed when there is a difference between the concentrations of a given substance. The movement of substances in diffusion occurs from a region of higher concentration to a lower concentration. This is a downhill process and thus occurs passively. It occurs mainly in liquids and gases as they have molecules that undergo random movement. The diffusion of one substance is independent of the diffusion of other substances. This process continues till both regions have similar concentrations, and the concentration gradient is zero.
Diffusion is mainly of two types-

1)Simple diffusion- The movement of molecules from higher concentration to lower concentration across a semipermeable membrane. Example- Excretion of urea into the blood in the liver.
2)Facilitated diffusion- The movement of molecules from a region of higher concentration to its lower concentration across a biological membrane, with the help of a carrier molecule or transmembrane integral protein. Example- Transportation of glucose and amino acids from the blood into the cell.

Factors that affect diffusion are-
1)Temperature- An increase in temperature results in increased kinetic energy of the molecule. The molecules move at a faster rate, and thus the rate of diffusion will increase.
2)Size of the particles- The particles with a larger size will be denser and thus will move slowly. Therefore, they will have a decreased rate of diffusion.
3)Concentration gradient- More concentration gradient results in a higher rate of diffusion and vice versa.
4)Membrane permeability- High density membranes or smaller areas of interaction for molecules decreases the rate of diffusion. These two factors provide hindrance for the movement of the molecules.

Common examples of diffusion are-
a)Diffusion of oxygen from the inhaled air to the lungs and bloodstream.
b)Diffusion of carbon dioxide from the body tissues to the bloodstream.
c)Diffusion of ions across the neural membrane that generates an electrical signal or impulse.
d)Diffusion of lipids in the epithelial cell lining of the small intestines.
e)Filtration of waste materials into the nephrons in the kidney.

Note: Diffusion is often confused with a similar process called Osmosis. Diffusion allows the movement of both- solute and solvent molecules along the concentration gradient. A semipermeable membrane is not mandatory for this process.
Osmosis is the movement of solvent molecules(only) from a region of a higher concentration to a region of lower concentration across a semipermeable membrane (only).