Important terms:
1.
Anti –transpirants: Chemical
substances that reduce transpiration without
affecting the gaseous exchange.
2.
Adhesion: The attraction between the
molecules of dissimilar substances.
3. Apoplast (Munch 1931): Refers
to non-living complex of the plant made of cell walls, intracellular spaces and
water filled xylem channels.
4. Cohesion: The attraction between the molecules of
the same substances.
5. Capillary Water: The
water held against the force of gravity in the capillary like spaces between
the soil particles.
6. Diffusion: Movement
of particles, ions or molecules from the region of their higher concentration
to the region of their lower concentration.
7. Diffusion Pressure Deficit (DPD):
The
amount by which diffusion pressure of water in a solution is lower than that of
pure water.
8. Guttation:
The exudation of liquid drops from the margins of leaves through hydathodes in
certain plants.(supposed to be due to root pressure).
9. Matric Potential (Imbibition potential): Refers to the
reduction in chemical potential of water due to imbibitions by hydrophilic
colloids.
10. Osmosis:
The movement of water molecules from a region of their higher concentration to
the region of their lower concentration through a semi permeable membrane.
11. Osmotic Pressure (OP):
The pressure which would develop in a solution when, the solution is separated
from its pure solvent by a semi permeable membrane.
12. Photoactive Stomata: Stomata
opening in response to the presence of light.
13. Root pressure:
The pressure that develops in the root due to active absorption of water, which
brings about pushing of xylem sap.
14. Symplast: Refers
to living complex of the plant formed by protoplasts connected through
plasmodesmata.
15. Scotoactive Stomata: Stomata
opening in dark.
16. Transpiration:
The loss of water in the form of water vapour from the aerial parts of the
plant.
17.Tensile Strength of water:
It is the ability of water column to get stretched without breaking. Tensile
strength is due to cohesive force amongst molecules of water and adhesion
between water molecules and wall of xylem. Its value is 45-207 atm. (Dixon and
Joly, 1894).
18. Water potential:
The differences between the free energy of water molecules in pure water and
the energy of water molecules in other system.
19. Wilting:
Drooping of the leaves and young shoots, when the water loss is more than the
uptake of water by the roots.
Additional Information
1.
Standard solution: A solution containing known weight of
the substance dissolved in a known volume of solvent.
2.
Molar solution: One gram molecular
weight of a solute dissolved in solvent to make final volume of solution
exactly one litre.
3.
Molal Solution: One gram molecular weight of a solute
dissolved in 1 litre of the solvent.
4.
Zero Values: DPD or water potential is zero in a
fully turgid cell placed in water. Turgor
pressure (TP) or pressure potential
becomes zero, when a cell is placed in hypertonic solution. Osmotic pressure (OP) cannot become
zero in a cell. It is only in case of pure water.
5.
Relative Humidity and Stomata: Stomata close down if
relative humidity of atmosphere falls below 50%. They remain open at R. H.
above 70%.
6.
Psychrometer: An instrument used for measuring both
relative humidity and transpiration.
7.
Tensiometer: Instrument used for measuring soil
water tension.
8.
Atmometer: An apparatus for demonstrating and measuring pull
caused by evaporation of water from a porous pot.
9.
Absorption Leg (Kramer, 1973) – It is the short fall
of rate of water absorption over the rate of transpiration. It is due to high
rate of transpiration during midday, development of water deficit around root
hairs and resistance in the movement of water inside the plant.
10.
Wilting in Waterlogged Soils: Wilting of plants in
waterlogged soils is caused by the development of ethylene precursor by the
roots (Bradford and Young, 1981), which on reaching the
shoot brings about wilted condition.
11.
Potometer: It is an apparatus for measuring the rate of
transpiration.
12.
Porometer: An apparatus for measuring the relative sizes of
stomata.
13. Drought: A dry spell of weather and sustained period of significantly subnormal water or soil moisture supply to the plants.
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