Hypertonic Solution Vs. Hypotonic Solution

Guttation is a process in which sap exudes out on the tips of leaves, commonly mistaken as dew in the morning. This occurs in the evening or early mornings as the rate of absorption of water exceeds the rate of transpiration. The excess water is exuded.

Osmosis is basically the movement of solvent molecules that are present in a solution through a selectively permeable membrane such that there is an equal concentration of the solvent molecules across the membrane.

In biological systems, the solvent is usually water. Nutrients and oxygen are taken in the cell from the surroundings by the process of osmosis, and waste products and carbon dioxide are given out of the cell. It also helps in maintaining the concentration of solutes inside the cell by maintaining the balance of water across the cell membrane.

This balance is maintained by maintaining its osmotic pressure.
Osmotic pressure can simply said to be the pressure exerted by the flow of water on the semipermeable membrane through which it flows.

Solutions can be classified into:

Isotonic solution: When the concentration of the two solutions separated by a semipermeable membrane is the same, i.e., the concentration of the solution outside the cell is equal to the concentration of the cytoplasm. Therefore, there is no net flow of solvent molecules across the semipermeable membrane.

Hypertonic solution: When the concentration of solutions separated by a semipermeable membrane is unequal, i.e., the solution outside the cell is more concentrated than the cytoplasm of the cell.

Hypotonic solution: When the concentration of solutions that are separated by a semipermeable membrane is unequal, the solution outside the cell is more dilute than the cytoplasm of the cell.

★ In a hypertonic solution, the concentration of the solute is greater outside the cell membrane.

★ The concentration of the solute is greater inside the cell membrane in a hypotonic solution.

★ Solvent molecules undergo exosmosis, i.e., solvent molecules flow outside the cell through a semipermeable membrane.

★ Solvent molecules undergo endosmosis, i.e., solvent molecules flow inside the cell through a semipermeable membrane.

★ As solvent molecules flow outside the cell, the cell shrinks in size.
★ In plant cells, the protoplasm shrinks and is only attached to certain points on the cell wall through the plasmodesmata. This is called plasmolysis.

★ As solvent molecules flow from outside the cell to inside, the cell swells.
★ Large intake of water by animal cells cause the cells to swell and even burst. This is called cytolysis. In plant cells, the cells take in water and swell, and are said to be turgid.

★ 10% dextrose (D10W) IV solution is an example of hypertonic solution (normal concentration of dextrose in blood is 5%) that is administered to some patients.

★ Marine fish live in a hypertonic environment and lose a large amount of water due to exosmosis. In order to maintain their osmotic balance, these fish constantly take up large amount of water from their surrounding and excrete large amounts of salts.

★ In dehydration, the body loses a large amount of water, leading to reduction in the volume of water present in cells with the result that the cells become hypertonic.
★ 0.45% NaCl (0.45% NS) IV solution is an example of hypotonic solution that is administered to patients with severe dehydration.

★ Freshwater fish live in a hypotonic environment and take up a large amount of water due to endosmosis. In order to maintain their osmotic balance these fish excrete large amounts of water.

★ The root cells of plants have a high concentration of minerals in them, making their surroundings hypotonic. This causes an influx of water molecules inside the roots and helps the roots to take up water molecules from their surroundings.

Hypertonic mannitol solution is used to treat cerebral edema and reduces the intracranial pressure that may arise during brain injury. Thus, it may prevent further damage to the brain. The use of hypertonic NaCl solution has seen to be beneficial in improving the blood flow in patients during a cardiac surgery.

Hypotonic NaCl solution is used to treat hypernatremia, a condition in which serum concentration of sodium is high as well as in the treatment of patients suffering from severe dehydration. It is also used in liposuction.

Salting is a process used for drying foods. In this, the food is covered with salt which creates a hypertonic environment that draws out the moisture from the foods by exosmosis. This prevents microbial growth on the food. In pickled or cured foods and jellies, the high concentration of the salt or sugar prevents the growth of any bacteria or fungi. This, therefore, prevents the food from spoiling.

In both processes, there is movement of water molecules across the cell membrane so that the cell can achieve isotonicity. This process takes place spontaneously without the expenditure of the cell's energy and is called passive transport.