Diffusion: Definition, Meaning, Functions, Types, Topics, Example

What is Diffusion?

The diffusion process is characterized by the transfer of particles, molecules, or ions from an area of high to one of low concentration, following a concentration gradient. Diffusion continues until it reaches equilibrium and the concentration of the particles in that space is uniform. This is a fundamental physical process that transfers substances across cell membranes and within cell compartments, which even plays a key role in a variety of biological and chemical events.

Basic Principles of Diffusion

The basic principle of the diffusion process includes:

Brownian Motion

Particles are in constant and random motion. This random movement of molecules is called Brownian motion. It is this random motion that leads to the slow, progressive dispersion of particles from higher to lower concentration areas.

Concentration Gradient

Concentration gradient is a difference in the concentration of particles in two regions. The concentration gradient is, therefore, the driving force behind diffusion, with movement from areas of high to low concentrations to equate the concentration.

Dynamic equilibrium

The equilibrium in the process of diffusion refers to the state when the concentration of the particles within a space has become uniform. The rate of movement in one direction then becomes equal to the rate of movement in the other direction and is called dynamic equilibrium—no net movement but continued molecular motion.

Types of Diffusion

The different types of diffusion are:

Simple Diffusion

During simple diffusion, molecules travel straight across a semipermeable membrane from an area of higher to that of a lower concentration without any energy or transport proteins. It is through simple diffusion that the exchange of oxygen and carbon dioxide happens in the lungs. These gases diffuse across the cell membranes to balance out the gases in the blood and the alveoli.

Facilitated Diffusion

Some transport proteins of the membrane aid in the facilitated diffusion, causing the motion of molecules from high to low-concentration areas. This kind of transport mechanism is applied in the case of those molecules which cannot easily travel through the lipid bilayer.

Examples: An example includes glucose, which goes into the cells being transported via carrier proteins. The channels and carriers, in turn, provide a way for these molecules to cross efficiently across the membrane.

Osmosis

Osmosis is a unique form of diffusion in which water molecules move through a semi-permeable membrane from an area with a low concentration of solutes to an area with a high concentration of solutes. It is central to the maintenance of cellular homeostasis.

Solutions are categorized by their relative concentrations of solutes.

• Isotonic solutions have equal concentrations of solutes inside and outside the cell, so no net movement of water occurs.

• A hypertonic solution has a higher concentration of solutes outside the cell than inside, resulting in possible shrinkage of the cell as water leaves it.

• A hypotonic solution has a lower concentration of solutes outside the cell than inside it and water enters the cell with the result of possible swelling or bursting of cells.

Factors Affecting Diffusion

Diffusion is affected by the following factors:

Concentration Gradient

This is the difference in concentration of some substance in two different regions. The greater the difference in concentration—the steeper the gradient—then the faster the molecules will move from an area of high to an area of low concentration in attempts at achieving equilibrium.

Temperature

The temperature increases the kinetic energy of molecules. Hence, raising the temperature increases the speed of the molecules. While the molecular speed increases, so does the rate of diffusion. With a temperature rise, there will, generally, be a faster rate of diffusion since these molecules would hit each other more often and would thus spread faster.

Particle Size

Smaller molecules diffuse faster than larger ones since of their smaller size, they meet less resistance while diffusing across the medium. The larger the molecule, the less its ability to easily pass through the spaces in whatever medium is used for diffusion, hence a slower diffusion rate.

Nature of Medium

The nature of the medium through which diffusion takes place affects the rate too. In gases, the rate is higher because their density is lower and the movement of their molecules is more as compared to liquids and solids. In liquids, the rate is slow because the molecules are more closely packed and thus face more resistance.

Examples of Diffusion

The examples of diffusion:

• When a tea bag is submerged in hot water, the water colour changes as the tea bag diffuses into it.

• We may detect the odour by the way a perfume or room freshener spray diffuses into the air.

• Without stirring, sugar dissolves uniformly and sweetens the water.

• The smoke from the incense stick diffuses into the air and fills the space as we light it.

• When boiling water is added to dry noodles, the water diffuses and rehydrates the noodles, giving them a plumper, more saturated texture.

Causes of Diffusion

Diffusion is a physical and natural phenomenon that occurs naturally without the solutions being shaken or stirred. Diffusion occurs in liquids and gases because molecules can flow at random. The molecules alter their course as they collide with one another.

Significance of Diffusion in Biology

One significant process involved in various life processes is diffusion. It is the net movement of particles, ions, molecules, solution, etc., as was previously stated. Diffusion is a crucial component of the movement of molecules during cellular metabolism in all living things.

This process aids in the diffusion of carbon dioxide gas into the bloodstream through the cell membrane during respiration. In plant cells, diffusion also takes place. Water from the soil permeates all green plants through the cells that make up their root hairs.
Diffusion is the process by which ions migrate between neurones to produce electrical charge.

Diffusion vs Osmosis – Quick Comparison Table

The difference between diffusion and osmosis are:

Diffusion NEET MCQs (With Answers & Explanations)

Important topics for NEET exam are:

• Types of Diffusion

• Factors Affecting Diffusion

Practice Questions for NEET

Q1. Diffusion is the result of concentration gradient which refers to

1. Change of concentration with respect to time

2. Change of concentration with respect to space

3. Change of concentration with respect to temperature

4. Change of concentration with respect to gravity

Correct answer: 2) Change of concentration with respect to space

Explanation:

Movement of all substances from the area of their higher free energy to the area of their lower free energy along the concentration gradient. Neutral solutes move across the membranes by diffusion. The net direction of diffusion of particles depends on their concentration in a particular region or space.

Hence, the correct answer is option 2) Change of concentration with respect to space.

Q2. Why does an increase in temperature increase the rate of diffusion?

1. The increased thermal energy of the medium reduces the kinetic energy of particles

2. The decreased thermal energy of the medium increases the kinetic energy of particles

3. The increased thermal energy of the medium does not change the kinetic energy of particles

4. The increased thermal energy of the medium increases the kinetic energy of particles

Correct answer: 4) The increased thermal energy of the medium increases the kinetic energy of particles

Explanation:

Higher the thermal energy in a medium: this raises the kinetic energy of its particles resulting in faster diffusion. The more heat there is, the more violent motion the particles perform the more collisions they experience, and the better the diffusion becomes as particles spread out and mix with others. Such a process plays a very significant role in biological and chemical systems, for example, in the transport of molecules, gases, and ions that determine the rate of chemical reactions and dynamics of systems.

Hence the correct answer is option 4) The increased thermal energy of the medium increases the kinetic energy of particles.

Q3. Which of the following has the maximum diffusion pressure?

1. Cell sap

2. Rainwater

3. Ice caps

4. All of these

Correct answer: 2) Rainwater

Explanation:

Pure water has a maximum diffusion pressure of 1236 atm, meaning it has the highest tendency to diffuse and move freely. When solutes are added, the diffusion pressure decreases, leading to a reduction in water potential. This works on the principle that during osmosis, the water moves from a region of higher diffusion pressure (pure water) to a region of lower diffusion pressure (solution).

Hence, the correct answer is option 2) Rainwater.

Also Read:

• MCQs on Diffusion

• Transport in Plants

• Reverse Osmosis

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