Biology is all about functions and differences. Students are often asked to explain the differences and similarities in CBSE exams. Amongst several modes of transportation, osmosis, diffusion, and active transport are the most vital Biology concepts. The difference between diffusion and osmosis has been asked several times in class 11 and 12 exams. Students can also expect related questions in NEET 2022. Students must list down the key difference between diffusion and osmosis to create a proper contrast between the two forms of transport. However, you need to revise the definitions of diffusion and osmosis and get well-versed in the topics before comparing. Here is what we will cover in the article:
What is Diffusion?
The scientist who coined the term: Robert Brown
Definition: Diffusion is the movement of any substance from its higher concentration to a lower concentration by random movement of ions or molecules of the substance.
Therefore, the movement of molecules is along the concentration gradient. The molecules’ movement continues until the molecular concentration in all the available space becomes the same.
Kinetic energy is the force involved in the diffusion of molecules. The definition can also be put as follows:
Diffusion is the movement of molecules from their higher kinetic energy to their lower kinetic energy.
However, students must remember that diffusion is a passive process and does not require energy expenditure.
There are two main types of diffusion: simple diffusion and facilitated diffusion.
- Simple diffusion: The particles diffuse without any additional support. It usually involves the movement of small size particles.
- Facilitated diffusion: The diffusing articles require the support of transmembrane proteins. Thus, this type of diffusion also favours large particles’ movement.
Factors Affecting Diffusion
Several factors influence the rate of diffusion. Some key factors influencing the diffusion rate are as follow:
- Concentration gradient
- Distance between the two regions
- Area of diffusion
- Size of molecules
- Solubility
- Pores in a membrane
Thus, the rate of diffusion gets faster when:
- The difference in the concentration gradient is increased
- The distance between the two regions is increased
- The area over which diffusion occurs is increased
- Small size molecules are diffusing
- The molecules are fat-soluble
- The size of pores in a cell membrane is larger, and so is their number
Students must note that the diffusion of one substance or compound is independent of the presence of the other substance or compound present in the same medium. For instance, many gases diffuse in the air simultaneously at their diffusion rates.
Examples of Diffusion
Diffusion occurs in our day-to-day life. Some common examples of diffusion are as follows:
- When sugar dissolves in water, its molecules distribute evenly across the liquid giving a uniform sweet taste.
- A spray of perfume in one corner of the room reaches the other via diffusion. The molecules of the perfume diffuse through the molecules of air.
- When a food colour is dropped into a liquid, the entire liquid changes its colour quickly due to the diffusion of food colour molecules.
Role of Diffusion in Plants and Animals
It is important to understand the concept of diffusion in plants and animals as it plays a vital role in several life processes.
Diffusion in Plants
- It helps in the exchange of gases during photosynthesis and respiration.
- The water vapours diffuse from the intercellular spaces to the atmosphere in transpiration.
- Diffusion occurs in passive salt uptake.
Diffusion in Animals
- Diffusion of glucose and oxygen in and out of cells
- Gaseous exchange during respiration
What is Osmosis?
The scientist who coined the term: Abbe Nollet
Definition: Osmosis is the net movement of water molecules from their region of higher concentration to their region of lower concentration via a semipermeable membrane.
Osmosis can also be defined as:
The movement of water molecules via a differentially permeable membrane from low solute concentration to the region of higher solute concentration.
Thus, osmosis is a passive process, and it does not require any additional energy.
Osmotic pressure is another important term related to osmosis. Osmotic pressure is the hydrostatic pressure that balances and prevents further osmotic inflow of water in the concentrated solution.
The two types of osmosis are:
Endosmosis: When a cell is placed in a hypotonic solution or water, the water molecules from outside the cell move inside the cell via a semipermeable membrane. This process is called endosmosis. Thus, the cell becomes turgid as the osmotic pressure increases inside the cell.
Exosmosis: When a cell is placed in a hypertonic solution, the water molecules have a higher concentration inside the cell. Thus, water molecules move from inside the cell to outside the cell. Thus, the cell becomes flaccid.
Factors Affecting Osmosis
The key factors influencing osmosis are:
- The concentration of the liquid solutions
- Temperature
- Ionisation of solute molecules
- Surface area
- The difference in water potential
- Pressure
- Light and dark
The rate of osmosis gets faster when:
- The concentration gradient is lower
- The temperature increases
- Ionisation of solute molecules increases
- The surface area is larger, and the molecules get more space to move across.
- The difference in water potential is higher
- Pressure increases
- The light is brighter
Examples of Osmosis
Some common examples of osmosis from daily life are:
- Swelling of raisins when placed in water due to endosmosis
- Potato in sugar solution shrinks due to exosmosis
Significance of Osmosis
Osmosis has a crucial role to play in both plants and animals.
In Plants
- It helps in the absorption of water from the soil.
- Maintain turgidity of the cells
- Assists opening and closing of stomata and thus affects photosynthesis and transpiration.
- Prevents plants from freezing.
In Animals
- Helps to get nutrients out of food
- Assists in the removal of waste products from the blood.
Difference Between Diffusion and Osmosis
The following table enumerates the most important points of difference between diffusion and osmosis.
Osmosis | Diffusion |
It takes place in the liquid medium only. | It occurs in liquid, gas, and solids. |
It needs a semipermeable membrane. | It does not need a semipermeable membrane. |
It is affected by the number of solute particles present in the solvent. | It is affected by the presence of other particles. |
It needs water for particles’ movement. | It does not require water. |
Diffusion of only solvent molecules occurs. | Diffusion of both the molecules of solute and solvent takes place. |
One directional flow of particles. | Particles flow in all the directions. |
On applying additional pressure on the solution side, we can stop or reverse the entire process. | Diffusion cannot be stopped or reversed. |
Takes place only between similar solutions. | Takes place between both the similar and dissimilar solutions. |
The concentration of the solvent does not attain equality on the two sides of the membrane. | The concentration attains equality in the available space. |
It depends on solute potential. | It doesn’t depend on solute potential. |
Diffusion and Osmosis in NEET Exam
Students must study the two topics for their NEET exam. Several Botany and Zoology MCQs for NEET revolve around diffusion and osmosis. Therefore, students must not miss out on the two topics, their related terms, and points of differences and similarities.
They can go through NCERT Solutions for Class 11 Biology to check answers to the important questions per the latest NEET Biology Syllabus.
It is best to keep NCERT Solutions for Class 11 handy when preparing for NEET or other exams.
Bottomline
Osmosis and diffusion are two types of transport systems for the movement of molecules both inside and outside of the cells. The two systems have a few similarities, such as their nature; both are passive, i.e., they do not involve energy expenditure (facilitated diffusion is an exception as it requires ATP). The most prominent differences stand out and make the two transport systems different. The difference in the medium in which diffusion and osmosis operate, the involvement of a membrane in osmosis are some of the most striking differences between diffusion and osmosis.