Osmosis is a process by which the molecules of a solvent pass from a solution of low concentration to a solution of high concentration through a semi-permeable membrane. It is a passive process and happens without any expenditure of energy.
There are three different types of solution:
An isotonic solution is one that has the same concentration of solutes both inside and outside the cell.
A hypertonic solution is one that has a higher solute concentration outside the cell than inside.
A hypotonic solution is the one that has a higher solute concentration inside the cell than outside.
Types of Osmosis
Osmosis is of two types:
Endosmosis– When a substance is placed in a hypotonic solution, the solvent molecules move inside the cell and the cell becomes turgid or de-plasmolyzes. This is known as endosmosis.
Exosmosis– When a substance is placed in a hypertonic solution, the solvent molecules move outside the cell and the cell becomes flaccid or plasmolyzes. This is known as exosmosis.
Effect of Osmosis on Cells
Osmosis affects the cells differently. An animal cell will lyse when placed in a hypotonic solution compared to a plant cell. The plant cell has thick walls and requires more water. The cells will not burst when placed in a hypotonic solution. In fact, a hypotonic solution is ideal for a plant cell.
An animal cell survives only in an isotonic solution. In an isotonic solution, the plant cells are no longer turgid and the leaves of the plant droop.
The osmotic flow can be stopped or reversed, also called reverse osmosis, by exerting an external pressure to the sides of the solute. The minimum pressure required to stop the solvent transfer is called the osmotic pressure.
Osmotic pressure is the pressure required to stop water from diffusing through a membrane by osmosis. It is determined by the concentration of the solute. 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.
Osmotic pressure can be calculated using the equation:
where Π denotes the osmotic pressure,
M is the molar concentration of the solute,
R is the gas constant,
T is the temperature
Significance of Osmosis
- Osmosis influences the transport of nutrients and release of metabolic waste products.
It is responsible for the absorption of water from the soil and conducting it to 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 turgor 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.
Examples of Osmosis
The absorption of water from the soil is due to osmosis. The plant roots have a higher concentration than the soil, therefore, the water flows into the roots.
The guard cells of the plants are also affected by osmosis. When the plant cells are filled with water, the guard cells swell up and the stomata open.
If a freshwater or saltwater fish is placed in the water with different salt concentration, the fish dies due to entry or exit of water in the cells of the fish.
Humans suffering from cholera are also affected by osmosis. The bacteria that overpopulate the intestines reverse the flow of absorption and does not allow water to be absorbed by the intestines, which results in dehydration.
When the fingers are placed in water for a longer period of time, they become pruney due to the flow of water inside the cells.
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|Difference between endosmosis and exosmosis||Difference between osmosis and diffusion|
|Plant Water Relations||Passive Transport|
Frequently Asked Questions
How do you define osmosis?
Osmosis is the movement of solvent from a region of lower solute concentration to a region of higher solute concentration through a semi-permeable membrane.
What are the three types of osmotic conditions that affect living cells?
The three types of osmotic conditions include- hypertonic, isotonic, and hypotonic.
What are the different types of osmosis?
The different types of osmosis include- endosmosis, where when a substance is placed in a hypotonic solution, the solvent molecules move inside the cell and the cell becomes rigid. Exosmosis, where when a substance is placed in a hypertonic solution, the solvent molecules move out of the cell and the cell becomes flaccid.
Why is osmosis important for the cells?
Osmosis is important for the cells for many reasons. It helps in the movement of important materials inside and out of the cell. The important nutrients and water dissolved moves in and out of the cell by osmosis.
How is osmosis different from diffusion?
Osmosis is a process that occurs through a semi-permeable membrane from a region of low solute concentration to high solute concentration. On the contrary, diffusion does not require a semi-permeable to occur, and the molecules move from a region of higher concentration to lower concentration.
Do dead cells exhibit osmosis?
Yes, dead cells also exhibit osmosis. If a dead cell is placed under a hypotonic solution, water moves inside the cell and it bulges.
What is the main function of osmosis?
Osmosis helps in stabilising the internal environment of the organism by balancing the levels of water and intracellular fluids. Also, the nutrients and minerals enter the cell by osmosis which is necessary for the survival of cells.