Osmosis

Osmosis is a biological and chemical process in which there is passive movement of solvent molecules from a region of lower solute concentration to a region of higher solute concentration through a semipermeable membrane, thus equalizing solute concentrations on both sides of the membrane. The osmosis process is essential for many biological processes, including the absorption of nutrients and the maintenance of the fluid balance in cells and organisms.

Osmosis Definition

Osmosis is the passive movement of a solvent, through a semi – permeable membrane, from a region of higher solvent concentration to a region of lower solvent concentration, equalizing the concentrations on both sides.

What is Osmosis?

Osmosis is the movement of molecules from a region of higher concentration to a region of lower concentration through a semipermeable membrane until equilibrium is reached. The Osmotic phenomenon was discovered in 1748 by Nollet. Osmosis is a type of passive transport, that is, it doesn’t require energy from outside and can occur spontaneously. The process occurs naturally in the biological system, such as nutrient uptake in plant roots and maintaining cell turgor pressure.

The process of osmosis is driven by the water potential gradient, which depends on pressure potential and solute potential. In humans, osmosis takes place in the process of kidney filtration, where waste products are removed from the blood after passing through semi – permeable membrane.

Osmotic Solution

Three types of osmotic solutions are present:

• Hypotonic Solution: A solution in which solute concentration is higher inside the cell than in the surroundings.
• Hypertonic Solution: A solution in which solute concentration is higher in the surroundings than the cell.
• Isotonic Solution: A solution in which the solute concentration is equal both inside and in the surroundings.

Types of Osmosis

• Endosmosis: Endosmosis occurs when the solute concentration inside the cell or system is higher than the surrounding environment, causing water to move inward to equalize the concentration. The cell becomes turgid or shows deplasmolysis.
• Exosmosis: Exosmosis occurs when the solute concentration inside the cell or system is lower than the surrounding environment, leading to the efflux of water to balance the concentrations. The cell becomes flaccid or shows plasmolysis.

Effect of Osmosis on Cell

Osmosis has a direct impact on cells. When a plant or animal cell is surrounded by a hypotonic solution, the animal cell can burst (lyse), while plant cells, with rigid cell walls and a greater need for water, maintain their structure. Animal cells find equilibrium in an isotonic solution, while plant cells lose their turgidity in such conditions.

Reverse osmosis, conversely, allows for the reversal of the osmotic process by applying external pressure, typically on the side with the solute. This pressure halts or even reverses the flow of molecules. The minimum pressure required for achieving reverse osmosis is referred to as osmotic pressure.

Osmotic Pressure

It is the minimum pressure needed to stop the moment through the semipermeable membrane. The osmotic pressure depends on the concentration of the solute. Osmotic pressure is calculated by using the equation:

π = MRT

• π=osmotic pressure
• M=molar concentration of solutes
• R=gas constant
• T=Temperature

Significance of Osmosis

 The biological significance of osmosis includes the following:

• Osmosis helps in maintaining the turgidity of cells.
• Dehiciesnce of fruit and sporangia occurred with the help of osmosis.
• High osmotic pressure helps the plant from drought.
• Osmosis helps in transpiration and excretion 
• Osmosis helps the roots to absorb water and nutrients from the soil.
• Osmosis stabilizes the internal environment of the cell by maintaining the water and intracellular fluids.
• Uptake of many ions via cell because of osmosis.
• Regulates the movement of plant cells.
• It is required for cellular survival.
• Osmosis plays an important role in seed germination.
• Water molecules are moved between the cell and the cell organelles.
• It is involved in moving water molecules from the soil into the root nodules in plants.
• The mechanism of stomata is primarily due to the guard cells’ response to osmotic pressure in relation to the epidermal cells.

Examples of Osmosis

It plays an important role in both plant and animal cells. Osmosis help in 

• Osmosis helps in the absorption of nutrients and water from the soil.
• Osmosis plays a role in facilitating the opening of stomata. When water concentration rises, guard cells begin absorbing water, causing them to swell and ultimately resulting in the stomata opening.
• Cholera-induced diarrhea in humans is a result of bacterial interference with osmosis. As the bacterial population grows, it triggers a reversal in the direction of water flow, reducing water absorption and ultimately causing diarrhea.
• Immersion of hands in water for a long time causes the fingers to wrinkle as water enters the cells through osmosis.

Factors Affecting Osmosis

The various factors affecting the process of osmosis are as follows:

• Osmotic Pressure: Osmosis can be counteracted by elevating the pressure in the region of high solute concentration in comparison to the region of low solute concentration. This pressure, known as osmotic pressure or turgor, represents the force per unit area required to prevent the flow of water or a highly liquid solution through a selectively permeable membrane into a more concentrated solution. Osmotic pressure is a colligative property, primarily dependent on solute concentration rather than its identity or content.
• Osmotic Gradient: The osmotic gradient signifies the difference in concentration between two solutions situated on opposite sides of a semipermeable membrane. It is used to calculate the percentage concentration of specific dissolved particles within a solution. It decides the direction and rate of osmosis.

Variation of Osmosis

• Osmosis (Reverse osmosis): This process employs pressure to drive a solvent through a semipermeable membrane while retaining solutes on one side. It forces pure solvent from an area of high solute concentration through the membrane to an area of low solute concentration, utilizing pressure greater than the osmotic pressure. Reverse osmosis is commonly used for water purification and desalination.
• Forward Osmosis: Osmosis is utilized to directly separate water from a solution containing undesirable solutes. A draw solution with higher osmotic pressure compared to the feed solution is employed to induce a net flow of water through a semipermeable membrane. This results in the concentration of the feed solution as the draw solution dilutes. The diluted draw solution can be used directly or subjected to a secondary separation process to remove the draw solute, which can be more efficient than using reverse osmosis alone.

Difference Between Osmosis and Diffusion

The Difference Between Osmosis and Diffusion is as follows:

Features	Osmosis	Diffusion
Definition	Osmosis is the specific type of diffusion that involves the movement of solvent molecules (usually water) through a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.	Diffusion is the general process of particle movement from an area of higher concentration to an area of lower concentration until equilibrium is reached.
Particles involved	Typically involves the movement of solvent molecules (e.g., water) across a selectively permeable membrane.	Involves the movement of any type of particles, such as solute molecules or gases, in a liquid, gas, or solid medium.
Selective barrier	Requires a semipermeable membrane to occur, where only certain molecules can pass through.	Can occur in the absence of a membrane or in an open system where particles can move freely.
Direction of movement	Moves solvent molecules from areas of lower solute concentration to areas of higher solute concentration until equilibrium is reached.	Moves particles from areas of higher concentration to areas of lower concentration until equilibrium is reached.
Energy requirement	Generally a passive process that does not require energy input (osmosis is passive transport).	Typically a passive process, but some types of diffusion, like facilitated diffusion, may involve protein channels and require minimal energy.

FAQs on Osmosis

1. What is Osmosis?

Answer:

Osmosis is the process of spontaneous movement of solvent molecules, usually water, across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.

2. What is the Significance of Osmosis in biology?

Answer:

Osmosis is vital for biological processes such as maintaining cell turgor pressure, nutrient uptake in plant roots, and regulating cell volume.

3. What is an Example of Osmosis?

Answer:

One common example is when raisins or grapes placed in a concentrated sugar solution swell as water from the fruit moves into the solution through osmosis.

4. What is Reverse Osmosis?

Answer:

Reverse osmosis is a process that uses pressure to force solvent molecules through a semipermeable membrane, effectively removing solutes and purifying the solvent. It’s used in water purification and desalination.

5. What is the Difference between Osmosis and Diffusion?

Answer:

Osmosis is a specific type of diffusion involving solvent molecules through a semipermeable membrane, while diffusion encompasses the movement of particles (solutes or gases) in any medium, often without a membrane.