ପରିବହନ ଓ ସଞ୍ଚାଳନ(TRANSPORTATION & CIRCULATION) Class 10 life science chapter-3 in odia || Part-3 ||

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Transportation In Plants

Transport in plants – plants are the type of organisms that have an autotrophic mode of nutrition. By taking in carbon dioxide from the air, minerals, and water from the soil, plants make their own food. After that, they release oxygen and water vapor. This process is Photosynthesis.

Plants use capillary action to bring up the water through the root and send it through the stem and branches. The molecules of water are attracted to the molecules inside the stem. Adhesive force contributes to capillary action, which causes a liquid column to rise inside a tiny capillary tube.

Mechanism of Ascent of sap


A number of theories have been put forward at various times to explain the mechanism of ascent of sap. These are (i) Vital theories, (ii) Root Pressure theory and (iii) Transpiration pull.



Vital Theories


These theories had been given very early and have only historical importance. Godslewski gave the relay pump theory. According to this theory the pumping of water takes place upwards due to the vital activities of xylem parenchyma and xylem rays.



J.C. Bose has put forward the pulsation theory. According to this theory water is pumped up due to the contraction and expansion of innermost cortical cells which creates a pulsation causing upward movement of water.



Transpiration Pull Theory


This is also called as cohesion-tension theory put forward by Dixon and Joly (1894) and supported by Renner, Curtis andClark. This theory is based on a number of features.



Cohesion and Adhesion


Mutual attraction between water molecules is called cohesion and this force may have a value as high as 350 atmospheres.



The wall of the tracheids and vessels which transport water are made up of lignin and cellulose and have high affinity for water and this is called adhesion.



Xylem vessels have perforated end walls and form a tubular structure from roots to the shoot tip. This provides a continuous channel for movement of water which cannot be pulled away from xylem wall due to cohesive and adhesive properties.



Transpiration Pull


The transpiration taking place through leaves causes negative pressure or tension in xylem sap which is transmitted to the root. This is called transpiration pull which is responsible for the movement of water column upward.