iv. Ringing experiment 4. 4 Transpiration pull theory. View Answer Answer: Pulsation theory 74 When the plant cells are fully turgid, the turgor pressure is equal and opposite to the The pressure developing in the tracheary elements of the xylem as a result of the metabolic activities of root is referred as root pressure. Due to this association many workers thought that ascent of sap was brought about in some manner by the living cells of the stem, although direct evidence in favor of this view was lacking. He thought that a rhythmic change in the water potential of the living cells like xylem parenchyma and medullary rays caused a pumping action to raise water vertically again. Jagadish Chandra Bose suggested a mechanism for the ascent of sap in 1927. Living cells like xylem parenchyma and ray cells remain intimately associated with the vessels and tracheid s. Due to this association many workers thought that ascent of sap was brought about in some manner by the living cells of the stem, although direct evidence in favor of this view was lacking. Cohesion- tension theory (Transpiration pull theory): This theory was put forth by Dixon and Jolly (1894). Upward movement of water takes place due to the periodic increase or decrease in the permeability of the living cells. According to him there was a rhythmic change in the osmotic pressure of the living cells of xylem parenchyma and medullary rays which brought about a pumping action of water in an upward direction. (4) Different theories have been discussed for translocation mechanism like vital force theory (Root pressure), relay pump. It seems almost incredible that insects could feed against such large tensions. Vital theories 5. Pulsation theory 7. These theories had been given very early and have only historical importance. Root Pressure Theory (Vital Theory): This theory was proposed by J. Priestley. Here, we review the recent literature on this topic with the aim of highlighting how a multi-disciplinary perspective has contributed to our understanding of the cohesion-tension theory of sap ascent in plants. VITAL FORCE THEORY According to these theories the forces required for ascent Of sap are generated in living cells of plants. This pulsation, according to him, caused the pumping of water from cell to cell in an upward direction. These are: (a) Vital theories (b) Root Pressure theory (c) Transpiration pull. He experimentally showed that the living cells of the innermost layer of the cortex were in a state of pulsatory motion, i.e., alternate expansion and contraction. i. Rolay pump theory : Godlewski (1884) proposed this theory. A brief account of various vital theories is given as follows: Godlewski (1884) proposed his clambering or relay-pump theory to explain the vertical movement of water through the plant. Answer. This theory however describes the movement of water from roots to the leaves of a plant. ii. •Godlewski’s relay pump theory •Pulsation theory •Root pressure theory 9 ... Imbibitional theory : ascent of sap takesplace due to imbibitional forces through walls ofxylem cells.•Magnitude of imbibitional force may be up to 1000atm,•But discarded due to fact that water moves inlumen of vessels rather than through the walls. i. These theories include Vital force theory, Relay pump theory, Physical force theory, Root pressure theory, etc. Cohesion- tension theory (Transpiration pull theory): This theory was put forth by Dixon and Jolly (1894). In modern textbooks it is assumed that transpi- ration pulls water from the roots to the leaves to heights greater than could be achieved by use of a vacuum pump… Godlewski proposed relay pump theory to explain ascent of sap. Root pressure theory. The theories are: These theories state that the vital capacity of the living cells is responsible for the ascent of sap. This is followed by an increase in water potential of the living cells and hence the absorbed water is pumped into the vessel element situated above and the process is repeated again and again, thus resembling a kind of staircase movement of water in the xylem. (3) The translocation occurs through Iumen of water conducting tissue xylem mainly vessels and tracheids. Relay pump theory and Pulsation theory support the active theory of ascent of sap. The following points highlight the three main theories regarding ascent of sap. Living cells like xylem parenchyma and ray cells remain intimately associated with the vessels, and tracheid s. Due to this association many workers thought that ascent of sap was brought, about in some manner by the living cells of the stem, although direct evidence in favor of this, Godlewski (1884) proposed his clambering or relay-pump theory to explain the vertical, movement of water through the plant. According to this theory, physical forces and dead cells are responsible for the ascent of sap. theory as being fundamentally correct, several important details about how plants deal with vascular stress remain unknown. The theories given in question are related with ascent of sap (the process of translocation of sap from the roots to the top of the plants). The pressure developing in the tracheary elements of the xylem as a result of the metabolic activities of root is referred as root pressure. 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