Diffusion of Gases

Introduction

How does the movement of gases occur? What principle do they follow. Lets us understand the process and how it occurs.

Diffusion is defined as the net movement of a substance or molecules from a region of higher concentration to a region of lower concentration.

Definition

Diffusion is defined as intermixing two or more gases at a given temperature, and pressure. It is random movement from the region of higher pressure to lower pressure along the concentration gradient. 

Concentration gradient is defined as concentration per unit length. Diffusion occurs in liquids and gases but hardly in solid. Diffusion occurs more quickly for gases than for liquids. Diffusion happens more quickly at warm temperatures than at colder temperatures.

Types of Diffusion

• Simple diffusion

A substance moves from a higher concentration to lower concentration in simple diffusion.It is a passive transport.Passive transport means that energy is not needed for the movement of the molecules.

• Facilitated diffusion

 Diffusion of a substance depends on its solubility in lipids.Cell membrane is made up of proteins and lipids. Substances that are soluble in lipids will diffuse through the membrane faster. Substances that are  hydrophilic will not easily pass through the  through the membrane.These molecules need to be facilitated to move across the membrane.This is done by facilitated diffusion.It is the passive movement of molecules across cell membranes (semipermeable) through certain protein channels, from higher to lower concentrations.

The protein channels may always be open or may be controlled.Some of the protein channels may be large to allow larger molecules to pass through.Plastids, mitochondria and some bacteria have certain proteins named as porins which allow the passage of small molecules across them

When proteins channels are used for transport of molecules,it can be of the following types-

Symport-Both  molecules move  across the membrane in the same direction.

Antiport-Both the molecules  move in opposite directions.

Uniport:Molecules move across the membrane independent of each other.

Comparison between simple and facilitated diffusion

In simple diffusion special transport channels not required, it is not selective and there is no uphill transport and it is a passive process i.e no energy is required for the movement of molecules to take place. While in facilitated diffusion special transport channels are required. It is selective and there is no uphill transport. It is a passive process i.e no no energy is  required for the movement of molecules to take place.

Osmosis 

It is a special type of diffusion in which the movement of  water molecules(solvent) occurs from a region of higher concentration to lower concentration across a semipermeable membrane.The rate of osmosis is affected by pressure gradient and concentration gradient.

Osmosis can take place in the cells through the following ways:

Endosmosis:The solution outside the cell has more amount of solvent.Such a solution is known as hypotonic solution.When a cell is placed in the hypotonic solution movement of solvent occurs from the outside to into the cell.

Exosmosis:The solution outside the cell has less amount of solvent as compared within the cell.Such a solution is known as hypertonic solution.When a cell is placed in the hypertonic  solution movement of solvent occurs from within the cell towards the outside.

Factors affecting diffusion

• Temperature-The increase in temperature increases the rate of diffusion.

• Pressure-With the increase in pressure, the rate of diffusion increases.

• Size of molecule or particles–Heavier particles will undergo slow diffusion while light   

molecules will diffuse faster.

• Concentration gradient-Diffusion occurs from higher to lower concentration.

• Permeability of the membrane-Diffusion usually does not need a membrane but for osmosis a semipermeable membrane is needed. Through a permeable membrane osmosis cannot take place.

Examples

Diffusion in humans

After breathing in, oxygen diffuses into the small blood vessels of lungs. Carbon dioxide will diffuse from blood vessels to the air sacs in the lungs. The digested food also passes from the small intestine into the blood capillaries by diffusion. Thus diffusion plays a very important part in the human body.

 Some more examples of diffusion are-

• Diffusion of waste products, salts, and water in the kidneys
• Gaseous exchange in lungs
• Dialysis: It is an artificial process that partially replaces renal function. Dialysis is based on the principle of diffusion of solutes and ultrafiltration of fluid across a semipermeable membrane.

Diffusion in plants

• Diffusion of gases takes place in the plants through the leaves.
• Intake of water takes place through the roots by osmosis.
• Transport of biomolecules and minerals in plants.

Everyday examples 

Adding boiling water to dried noodles

• During worship, we use an incense stick
• Sugar gets dissolved evenly in water
• Perfumes that we use for fragrance

Conclusion 

Thus diffusion is very useful in the separation of a variety of gases. Diffusion is also involved in a detection technique called the methane detecting process. Osmosis is also part of diffusion, which involves the infiltration of water by a technique called reverse osmosis. In our kitchens, the gas in LPG comes out by diffusion.

There are various types of diffusion like simple diffusion, facilitated diffusion, dialysis, osmosis.