OSMOSIS

 

OSMOSIS

Osmosis is a naturally occurring phenomenon which happens without any expenditure of energy and one of the most important processes in nature.

“It is a process where a weaker saline solution will tend to migrate to a strong saline solution.”

 OR

In easy way: It is the movement of solvent molecules from the region of lower concentration to the region of higher concentration through a semi permeable membrane.  Since water (H₂O) is solvent in every living being, biologists define osmosis as the diffusion of water across a selectively permeable membrane. The complete process does not require energy in order to take place.

  SOME EXAMPLES OF OSMOSIS ARE:

Ø Plants take water (H₂O) and minerals from roots with the help of osmosis. The guard cells of a plant cell are affected by osmosis. When plant cell is filled with water the guard cells swell up for the stomata to open and let out excess of water.

Ø When we keep raisins in water and raisin get puffed or swell up.

Ø If you are there in a bath tub or in water for long your finger gets pruned. Finger skin absorbs water and gets expanded.  

Ø Your sweat glands use osmosis. Your body doesn’t pump water to your skin in the form of sweat. Instead it deposits a little bit of salt inside of your sweat glands.

Photo by Jon Li from Pexels

SELECTIVELY PERMEABLE MEMBRANE:

The semi permeable membrane is a biological membrane it is the one that allows only specific ions and molecules to pass through, while it obstructs the movement of others.

 

OSMOTIC SOLUTIONS

There are three different types of solutions:

·        Isotonic solution

·        Hypertonic solution

·        Hypotonic solution

 

 

 

ISOTONIC SOLUTION

An isotonic solution is one that has the same concentration of solutes both inside and outside the cell.

 Means the condition is: if the medium surrounding the cell has exactly equal concentration of water as the cell, there will be no net movement of water across the cell membrane.

                                                Water moves the cell membrane in both the directions, but the amount of exchanging of water is same, so there is no overall movement of water. The cell will stay the same size.  

 

HYPERTONIC SOLUTION

A hypertonic solution is one that has a higher solute concentration outside the cell than inside and outside the cell.

 Means the condition is: if the medium has a lower concentration of water than the cell, meaning it is very concentrated solution, the cell will lose water by osmosis.

                                      Water molecules are free to moves the cell membrane in both the directions, but this time more water leaves the cell than it enters, therefore in this case the cell will shrink.

         

HYPOTONIC SOLUTION

A hypotonic solution is one that has a higher solute concentration inside the cell than outside the cell.

 Means the condition is: if the medium surrounding the cell has a higher concentration of water than the cell, meaning outside solution is very dilute than the cell will gain water by osmosis.

                                                Water molecules are free to moves the cell membrane in both the directions, but this time more water come into the cell than it leaves, therefore in this case the cell will swell up.

TYPES OF OSMOSIS

Osmosis is classified in three types:

·         ENDOSMOSIS

 When a substance is placed in a hypotonic solution, the solvent (water) molecules move inside the cell and the cell loses water and shrinks or undergoes deplasmolysis. This process is called endosmosis.

Examples:

o   Swelling of the raisins and grapes placed in water.

o   The absorption of water in the roots.

o   The absorption of water in the xylem vessels by the roots

 

·         EXOSMOSIS

 When a substance is placed in a hypertonic solution, the solvent molecules (water) move outside the cell and the cell becomes flaccid or undergoes plasmolysis. This process is called Exosmosis.

Examples:

o   Passage of water from root hair cells to cortical cells.

·         REVERSE OSMOSIS

Reverse osmosis is a natural phenomenon that happens in the opposite direction of the natural osmosis. This type of osmosis is used for removing the majority of contaminants from water by pushing the water under pressure through a semi-permeable membrane.

 

 

 

 

EFFECT OF OSMOSIS ON CELLS

Osmosis affects the cells of animal and plants distinctively.

1.   ANIMAL CELLS

Ø Animal cells (e.g. RBC, WBC etc.) placed in an isotonic solution, No osmosis occurs

Ø Animal cells (e.g. RBC, WBC etc.) in a hypotonic solution will gain water by osmosis, swell up and burst.

Ø Animal cells (e.g. RBC, WBC etc.) in a hypertonic solution will lose water by osmosis and shrink and shrivel.

 

2.   PLANT CELL

Plant cells have a cell wall that changes how the cell acts in responses to gaining and losing water (as we have studied, also known as osmosis).

 

Ø As we know that the plant has cell wall, which provides the cell additional support and protection that the animal cell does not have.

 

Ø A plant cell is able to stay the same size, when too much water leaves a cell by the process of Endosmosis.

 

Ø A plant cell will swell, when too much water enters the cell by the process of Exosmosis.

 

OSMOTIC PRESSURE

Osmotic pressure is the pressure necessary to stop water from diffusing through a membrane by osmosis. It is determined by the concentration of the solute. Osmotic pressure is defined as the pressure that must be applied to the solution side to stop fluid movement when a semi permeable membrane separates a solution from pure water. Water diffuses into the area of higher concentration from the area of lower concentration. When the concentration of the substances in the two areas in contact is different, the substances will diffuse until the concentration is uniform throughout.

IMPORTANCE OF OSMOSIS

• Osmosis influences the transport of nutrients and the release of metabolic waste products.

·         It is responsible for the absorption of water from the soil and conducting it to the upper parts of the plant through the xylem.

·         It stabilizes the internal environment of a living organism by maintaining the balance between water and intercellular fluid levels.

·         It maintains the turgidity of cells.

·         It is a process by which plants maintain their water content despite the constant water loss due to transpiration.

·         This process controls the cell to cell diffusion of water.

·         Osmosis induces cell turgid which regulates the movement of plants and plant parts.

·         Osmosis also controls the dehiscence of fruits and sporangia.

·         Higher osmotic pressure protects the plants against drought injury.

 

 

FACTORS AFFECTING THE RATE OF OSMOSIS

They are the following:

1.     Pressure.

2.     Temperature.

3.     Surface Area.

4.     Water Potential.

5.     Concentration gradient.

SOME EXAMPLES OF OSMOSIS:

·        The absorption of water from the soil is due to osmosis.

 

·        When a freshwater or saltwater fish is placed in the water with different salt concentrations, the fish dies due to way in or exit of water in the cells of the fish.

·        Feeling thirsty after having salty food.

 

·        The process of dialysis of kidney in the excretory system.

 

·        Movement of water and minerals from root nodules to various parts of plants.

Difference between Osmosis and Diffusion

OSMOSIS

·        It is occurs only in the liquid medium.

·        It requires a semi permeable membrane.

·        It depends on the number of solute particles dissolved in the solvent.

·        It involves water (H2O) for the movement of particles.

·        Only the solvent molecules are able to do diffusion.

·        The flow of particles occurs only in a single direction.

·        The whole process can either be stopped or reversed by applying additional pressure on the solution side.

·        It occurs only between similar types of solutions.

·        It involves the movement of only solvent molecules from one side to the other.

·        The concentration of the solvent does not become equal on both sides of the membrane.

·        It depends on solute potential.

·        Only water or another solvent moves from a region of high energy or concentration to a region of lower energy or concentration.

DIFFUSION   ·        It occurs in liquid, gas and even solids.

·        It does not require a semi permeable membrane.

·        It depends on the presence of other particles.

·        It does not need water for the movement of particles.

·        Both the molecules of solute and solvent are able to do diffusion.

·        The flow of particles occurs in all the directions.

·        This process can neither be discontinued nor reversed.

·        It occurs between the similar and dissimilar types of solutions.

·        It involves the movement of entire the particles from one region to the other.

·        The concentrations of the diffusion substance become equal to fill the available space.

·        It does not depend on solute potential, pressure potential, or water potential.

·        Any type of substance moves from area of highest energy or concentration to region of lowest energy or concentration.

·        It helps in the uptake of minerals and nutrients.   ALSO SHOULD  SEE THIS: Diffusion