chemical biology Chemical biology is a scientific discipline spanning the fields of chemistry and biology. The discipline involves the application of chemical techniques, analysis, and often small molecules produced through synthetic chemistry, to the study and ma ...

, tonicity is a measure of the effective

osmotic pressure Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane. It is also defined as the measure of the tendency of a solution to take in a pure ...

gradient; the

water potential Water potential is the potential energy of water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure and ...

of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective membrane-impermeable solutes across a cell membrane which determine the direction and extent of osmotic

flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...

. It is commonly used when describing the swelling-versus-shrinking response of

cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...

immersed in an external solution. Unlike osmotic pressure, tonicity is influenced only by solutes that cannot cross the membrane, as only these exert an effective osmotic pressure. Solutes able to freely cross the membrane do not affect tonicity because they will always equilibrate with equal concentrations on both sides of the membrane without net solvent movement. It is also a factor affecting imbibition. There are three classifications of tonicity that one solution can have relative to another: ''hypertonic'', ''hypotonic'', and ''isotonic''.A hypotonic solution example is distilled water.

Hypertonic solution

A hypertonic is when the concentration inside the cell is high and the environment is dilute. In biology, the tonicity of a solution usually refers to its solute concentration relative to that of another solution on the opposite side of a cell membrane; a solution inside of a cell is called hypertonic if it has a greater concentration of solutes than the cytosol inside the cell and its environment is dilute. So when the cell is hypertonic(concentrated) the cell needs more water, so water is forced to enter inside the cell and the cell will swell up and eventually burst. When plant cells lose water they are hypotonic, because their inside is diluted(with more water) and the environment is concentrated so it needs water then the flexible cell membrane pulls away from the rigid

cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...

, but remains joined to the cell wall at points called plasmodesmata. The cells often take on the appearance of a pincushion. In plant cells the terms isotonic, hypotonic and hypertonic cannot strictly be used accurately because the pressure exerted by the cell wall significantly affects the osmotic equilibrium point.

Hypotonic solution

A hypotonic is when the concentration inside of the cell is lower than a solution outside of a cell is called hypotonic. If it has a lower concentration of solutes inside a cell then water is forced to move out. Due to this, water is removed out of the cell causing shrinking of the cell membrane. For cells without a

such as animal cells, they lose water and shrivel. When plant cells are in a hypotonic solution, the central vacuole loses water and the cell membrane sticks against the cell wall.

Isotonicity

A solution is isotonic when its effective osmole concentration is the same as that of another solution. In biology, the solutions on either side of a cell membrane are isotonic if the concentration of solutes outside the cell is equal to the concentration of solutes inside the cell. In this case the cell neither swells nor shrinks because there is no concentration gradient to induce the diffusion of large amounts of water across the cell membrane. Water molecules freely diffuse through the plasma membrane in both directions, and as the rate of water diffusion is the same in each direction, the cell will neither gain nor lose water.

References

{{reflist Cell biology