Nearly 70% of the Earth’s surface is covered with water and it is generally recognized as a renewable resource and plant water relations. However the availability of fresh water still remains a limiting factor not only for plant growth but a major challenge for the entire human society as a whole (Blatt et al., 2014).
Importance of water for plants
- Water is a component of protoplasm.
- Water is one of the important medium of transport.
- It is participates in several metabolic reactions like photolysis of water, formation of carbohydrates during photosynthesis etc.
- Water maintains turgidity of plant cells.
- Mineral nutrients are absorbed by the plants from the roots in dissolved state where water acts as a solvent.
- Different organic constituents of plants as proteins, carbohydrates, enzymes loose their physical and chemical properties in absence of water.
- Water helps in mobility of gametes, dissemination of spores, fruits and seeds, provides support to aquatic plants.
- Water increases the rate of respiration.
- Seeds respire fast in presence of water which is important of for germination.
- Transpiration of water provides a cooling effect to the plants.
All important life sustaining activities of plant depend on water so it is termed as “Elixir of Life”.
Diffuse – to spread/ disperse/flow out or move in all directions.
Diffusion is the movement of particles (Ions, atoms or molecules) of different substances (solid, liquid and gases) from a region of higher concentration to a region of lower concentration due to their inherent kinetic energy till they get distributed uniformly and a dynamic equilibrium is attained.
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Osmosis is a special type of diffusion which occurs through membranes.
Osmosis is defined as the movement of water (solvent) from a region of its higher concentration to a region of its lower concentration through a semi-permeable membrane until a state of dynamic equilibrium is attained.
Why osmosis takes place?
Water diffuses through the semi-permeable membrane due to difference in diffusion pressure.
Diffusion pressure of pure solvent is higher while diffusion pressure of solution is lower due to addition of solute. Addition of solute lowers the diffusion pressure.
Water diffuses from a region of higher DP to lower DP.
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In a normal plant cell the protoplasm tightly pressed against the cell wall.
When a plant cell is placed in a hypertonic solution (solution of higher concentration than cell sap), Exo-osmosis occurs i.e., it loses water.
As concentration of the hypertonic solution increases cell loses more water, protoplasm shrinks and separates from the cell wall.
The shrinkage of the protoplasm from the cell wall under the influence of hypertonic solution is called as plasmolysis.
The space between the cell wall and the contracted protoplasm gets filled with the external solution.
Read More : Plasmolysis
The adsorption of water by hydrophilic colloids s is known as Imbibition.
Imbibition results in increase in the volume.
The substance which imbibes water and swells is termed as Imbibant e.g. seeds or wooden doors, windows etc. The liquid which is imbibed liquid is referred to as Imbibate.
Water can be imbibed both in liquid and vapour form.
Read More : Imbibition
FAQs : Plant Water Relations
1. What is Osmosis? Define.
2. What is Diffusion? Define.
Ans – Diffusion is the movement of particles (Ions, atoms or molecules) of different substances (solid, liquid and gases) from a region of higher concentration to a region of lower concentration due to their inherent kinetic energy till they get distributed uniformly and a dynamic equilibrium is attained.
References and sources