A) \[{{\psi }_{w}}={{\psi }_{m}}+{{\psi }_{s}}+{{\psi }_{p}}\]
B) \[{{\psi }_{w}}={{\psi }_{m}}+{{\psi }_{s}}-{{\psi }_{p}}\]
C) \[{{\psi }_{w}}={{\psi }_{m}}-{{\psi }_{s}}+{{\psi }_{p}}\]
D) \[{{\psi }_{w}}={{\psi }_{m}}-{{\psi }_{s}}-{{\psi }_{p}}\]
Correct Answer: A
Solution :
The difference between the free energy of water molecule in pure water and the energy of water in any other system (solution or plant tissue) is termed as water potential. Movement of water occurs from region of higher water potential to lower water potential. \[{{\psi }_{w}}={{\psi }_{s}}+{{\psi }_{m}}+{{\psi }_{p}}\] Its components are discussed below as follows: Matric potential : \[({{\psi }_{m}})\]is the term used for the surface (e.g., soil particles, cell wall, cell cytoplasm to which water molecules are adsorbed. In this case of plant cells and tissues it is usually disregarded because it is not significant in osmosis. Hence the above given equation is written as follows : \[{{\psi }_{w}}={{\psi }_{s}}+{{\psi }_{p}}\] Solute potential : \[({{\psi }_{s}})\] Also known as osmotic potential, it is denned as the amount by which the water potential is reduced as a result of the presence of solute. Solute potential is always negative number. Pressure potential : \[({{\psi }_{w}})\] Plant cell is elastic and it exerts a pressure on the cellular contents. As a result of inward wall pressure hydrostaic pressure is developed in the vacuole termed as turgor pressure. The pressure potential is usually positive and operates in plant cell as wall pressure.
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