Water potential is the potential energy of water relative to pure water (e. Potential energy can be thought of as Energy stored within a physical system Water is a common Chemical substance that is essential for the survival of all known forms of Life. g. deionized water) in reference conditions. It quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure, or matrix effects including surface tension. Osmosis is the Diffusion of a solvent (frequently water through a semi-permeable membrane, from a solution of low solute concentration (high water potential Gravitation is a natural Phenomenon by which objects with Mass attract one another Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface For the work of fiction see Surface Tension (short story. Surface tension is a property of the surface of a Liquid that causes it to Water potential is measured in units of pressure and is commonly represented by the Greek letter Ψ (Psi). For other uses see Psi. Psi (uppercase Ψ, lowercase ψ) is the 23rd letter of the Greek alphabet and has a This concept has proved especially useful in understanding water movement within plants, animals, and soil. Plants are living Organisms belonging to the kingdom Plantae. Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel
Typically, pure water at standard temperature and pressure (or other suitable reference condition) is defined as having a water potential of 0. The addition of solutes to water lowers its potential (makes it more negative), just as the increase in pressure increases its potential (makes it more positive). If possible, water will move from an area of higher water potential to an area that has a lower water potential.
One very common example is water that contains a dissolved salt, like sea water or the solution within living cells. These solutions typically have negative water potentials, relative to the pure water reference. If there is no restriction on flow, water molecules will proceed from the locus of pure water to the more negative water potential of the solution. This effect can be used to power a osmotic power plant. [1]
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Components of water potential
Many different potentials affect the total water potential, and sum of these potentials determines the overall water potential and the direction of water flow:
- Ψ = Ψ0 + Ψπ + Ψp + Ψs + Ψv + Ψm
where:
- Ψ0 is the reference correction,
- Ψπ is the solute potential,
- Ψp is the pressure potential,
- Ψs is the gravimetric component,
- Ψv is the potential due to humidity, and
- Ψm is the potential due to matrix effects (e. In Chemistry, a solution is a Homogeneous Mixture composed of two or more substances Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface Gravitation is a natural Phenomenon by which objects with Mass attract one another Humidity is the amount of water vapor in the air In daily language the term "humidity" is normally taken to mean Relative humidity. g. , fluid cohesion and surface tension. )
Pressure potential
Pressure potential is based on mechanical pressure, and is an important component of the total water potential within plant cells. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called Pressure potential is increased as water enters a cell. As water passes through the cell wall and cell membrane, it increases the total amount of water present inside the cell, which exerts an outward pressure that is retained by the structural rigidity of the cell wall. A cell wall is a tough flexible and sometimes fairly rigid layer surrounding a cell, located external to the Cell membrane, which provides the cell with structural
The pressure potential in a living plant cell is usually positive. In plasmolysed cells, pressure potential is almost zero. Negative pressure potentials occur when water is pulled through an open system such as a plant xylem vessel. In Vascular plants xylem is one of the two types of transport tissue Phloem being the other Withstanding negative pressure potentials (frequently called tension) is an important adaptation of xylem vessels. An adaptation is a characteristic of an Organism that has been favored by Natural selection and
Solute potential
Pure water is usually defined as having a solute potential (Ψπ) of zero, and in this case, solute potential can never be positive. The relationship of solute concentration (in molarity) to solute potential is given by the van 't Hoff equation:
- Ψπ = − miRT
where m is the concentration in molarity of the solute, i is the van 't Hoff factor, the ratio of amount of particles in solution to amount of formula units dissolved, R is the ideal gas constant, and T is the absolute temperature. The van 't Hoff equation (also known as the van 't Hoff isochore) in Chemical thermodynamics relates the change in temperature ( T) to the change in the In Physical chemistry, the van 't Hoff factor i is the number of moles of Solute actually in Solution per mole of solid solute added Relationship with the Boltzmann constant The Boltzmann constant kB (often abbreviated k) may be used in place of the gas constant by working
For example, when a solute is dissolved in water, water molecules are less likely to diffuse away via osmosis than when there is no solute. In Chemistry, a solution is a Homogeneous Mixture composed of two or more substances Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement Osmosis is the Diffusion of a solvent (frequently water through a semi-permeable membrane, from a solution of low solute concentration (high water potential A solution will have a lower and hence more negative water potential than that of pure water. Furthermore, the more solute molecules present, the more negative the solute potential is.
Solute potential has important implication for many living organisms. If a living cell with a lower solute concentration is surrounded by a concentrated solution, the cell will tend to lose water to the more negative water potential of the surrounding environment. This is often the case for marine organisms living in sea water and halophytic plants growing in saline environments. Marine is an Umbrella term. As an adjective it is usually applicable to things relating to the Sea or Ocean, such as Marine biology, Marine biosalinity|halophile A halophyte is a Plant that naturally grows where it is affected by Salinity in the root area or by salt spray such as in saline semi-deserts In the case of a plant cell, the flow of water out of the cell may eventually cause the plasma membrane to pull away from the cell wall, leading to plasmolysis. Rhoeo Discolor epidermisjpg|left|thumb|Before plasmolysis]] Plasmolysis is the contraction of cells due to the loss of water through Osmosis in plants and bacteria
Matrix potential
When water is in contact with solid particles (e. g. , clay or sand particles within soil) adhesive intermolecular forces between the water and the solid can be large and important. Clay is a naturally occurring material composed primarily of fine-grained Minerals which show plasticity through a variable range of Water content, and Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel Adhesion is the tendency of certain dissimilar molecules to cling together due to Attractive forces. In Physics, Chemistry, and Biology, intermolecular forces are forces that act between stable Molecules or between functional groups of A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. The forces between the water molecules and the solid particles in combination with attraction among water molecules promote surface tension and the formation of menisci within the solid matrix. For the work of fiction see Surface Tension (short story. Surface tension is a property of the surface of a Liquid that causes it to For other uses see Meniscus (anatomy and lens (optics. Meniscus, plural menisci, from the Greek for "crescent" Force is then required to break these menisci. For other uses see Meniscus (anatomy and lens (optics. Meniscus, plural menisci, from the Greek for "crescent" The magnitude of matrix potential depends on the distances between solid particles--the width of the menisci (see also capillary action)--and the chemical composition of the solid matrix. For other uses see Meniscus (anatomy and lens (optics. Meniscus, plural menisci, from the Greek for "crescent" Capillary action, capillarity, capillary motion, or wicking is the ability of a substance to draw another substance into it In many cases, matrix potential can be quite large and comparable to the other components of water potential discussed above.
It is worth noting that matrix potentials are very important for plant water relations. Strong (very negative) matrix potentials bind water to soil particles within very dry soils. Plants then create even more negative matrix potentials within tiny pores in the cell walls of their leaves to extract water from the soil and allow physiological activity to continue through dry periods. Transpirational pull is the main phenomenon driving the flow of Water in the Xylem tissues of large Plants Mechanisms Transpirational pull
References
http://www.colorado.edu/eeb/courses/4140bowman/lectures/4140-07.html
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