Why Plants Need Water?

Water is indispensable for living organisms including plants. Following is an account highlighting the key areas of significance of water in plant life vis-à-vis pattern of navigation in plant body:


Minerals from the soil in solid (particle) form can not be transported to aerial parts of a plant without the assistance of a fluid medium. Water offers both a medium for the minerals to dissolve and a vehicle to carry to different parts of plant.

Planting Why Plants Need Water?


Metabolic products too need water for their transport to parts where they are to be carried or required. Water under the impact of transpiration drags water all through xylem tissues. With the exception of a little fraction, less than 10%, nearly all the water entering the plant is lost through transpiration — a process in which water evaporates via leaves. Out of this 10% surviving fraction, some 5% is lost through cuticle.

The vitality of water for plant life is not just based on transpiration; it is more of the organic activities including metabolism going on in individual cell. Moreover, it is the fluid presence of water in plant cells that regulates not only their temperature but that of surroundings as well in extreme hot. It is to be noticed minutely that xylem tracks are so detailed that they are found even in the thinnest root track to all the way up to the aerial tips of the plant. How water rises against the gravitational pull is explained by the following theory:

The Cohesion-Tension Theory

In simpler terms, in the thin capillary tracts of xylem vessels there is a force of adhesion between the walls and the water molecules and cohesive force is in operation between water molecules themselves. These two pulls create a kind of surface tension successively along the length of xylem column and keep water dragging upward through a constant capillary action. At roots water enters the plant through osmosis, a process that operates on the principle of concentration gradient across two media. Moreover, in general, the potential difference of water across root and that of air around stomata in the leaves together exert an upward pull collectively known as transpiration. This is how water cycles through plant.


This is a process that designates a series of chemical reactions aimed at synthesizing food for plant cells. In the process, water reacts to provide a rich source of electrons. The chemical equation, the symbolic representation of the reaction goes as follows: -

6CO2 + 6H2O ® C6H1206 + 6O2

In the equation we can see that 6 molecules of each reactant, carbon dioxide and water combine to give us one molecule of glucose (the synthesized food) and six (06) molecules of oxygen as products, released to the air.


Photosynthesis is a Greek word which can be understood in terms of Photo (light) and Synthesis (composition — joining together). In the process CO2 is converted to glucose, an organic compound. The process gets its activation energy from floods of sunlight. The chemical reaction typically involved in photosynthesis releases oxygen (O2) as the waste product. This release of oxygen is essential to support life on earth. Photosynthesis is a chief natural means to consume CO2 hence contributing to reduce not only
aerial pollution but also global warming because CO2 being rich absorbent of heat is consumed and transformed to another organic compound in the process. In other words it regulates the level of oxygen and carbon dioxide in the atmosphere.

As for as the mechanics of the reaction is concerned, it begins from the absorption of light energy by proteins known as Photosynthetic Reaction Centers that possess chlorophylls. These proteins are found in sub-cellular organs (organelles) called chloroplasts. A certain fraction of light energy trapped by chlorophylls is deposited in the form of Adenosine Triphosphate (ATP) packets. The remaining amount of energy is dispensed in releasing electrons from water, a member of the reactants. The function of electrons owes its significance from their subsequent use in making chemical (covalent) bonds converting CO2 to organic compound (glucose in this reaction).


There are tiny apertures on the ventral surface of leaves that allow a steady evaporation of water. The process is essential to modulate the temperature of plant the way the temperature of animals is regulated by its counterpart, the perspiration. However, a balance is to be achieved between water retained in plant and the water lost. If excessive amounts of water are lost to the air, the leaves are likely to wilt and even turn pale / brown as a result of death of plant cells. It also gives mechanical support to stomata remain open for the intake of CO2.

There are two universal processes that go hand in hand for carrying water from the earth into the atmosphere, namely: evaporation and transpiration.

  1. Typically, EVAPORATION is a process in which the physical form of water shifts from liquid into gaseous state. The phenomenon of evaporation is based on the principle of relative humidity level across the leave surface, i.e. there should be less humidity in air compared with the internal environment of leave because if there is 100% humidity outside the leave surface, no evaporation will take place. It’s a kind of concentration gradient that flows from where there is greater presence of water molecules into where there is relatively low water concentration, as in open air. Moreover, a considerable amount of heat energy (here the sun light) is required for the process to take effect.
  2. Transpiration on the other hand is a similar process in which water, under the influence of evaporation and internal capillary action of xylem, escapes via stomata, small apertures, located at the ventral surface of leaves. Transpiration is a very slow process that depends on two factors: first, the rate of water evaporation at aerial locations and second, the rate of absorption of the mineral water at the roots. Interestingly, of all the water rooted via whole of the plant, just 1% is consumed in growth related activities / reactions. Over the course of transpiration, a range of required minerals are pumped to different parts of plant vis-à-vis preventing the plant from heat liberated as after a number of reactions out of which certain steps may involve a heat release.

Since it is difficult to hold sharp boundaries in defining the two processes, the botanists have derived a composite term “Evapotranspiration” to effectively explain phenomena, the evaporation and transpiration in plants. Following factors govern evapotranspiration: -

  • Humidity concentration
  • Wind Speed
  • Energy available
  • Water available


Turgidity is the measure of total pressure exerted by a plant cell against its cellular wall in the three dimensional space. The chief determiner of this pressure is directly proportional, in a recursive way, to the amount of water pressure in cellular contractile vacuole which is carried out under regular osmotic pressure, which is determined by Hydrostatic pressure resulting from the difference of concentration gradient across a semi permeable membrane.

The water present in all the cells exert pressure against their respective walls thereby constituting a collective pressure known as “Turgor Pressure”, the phenomenon being Turgidity. It is the Turgor pressure that provides a plant the essential mechanical support. Here the mechanical support is characterized by the factor of rigidity in plants. This rigidity is attained by the Turgor pressure in a plant cell which pushes the entire cytoplasm against the cell wall.

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