Merits and demerits of pressure flow hypothesis?
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Answer:
The pressure flow hypothesis, also known as the mass flow hypothesis, is the best-supported theory to explain the movement of sap through the phloem.[1][2] It was proposed by Ernst Münch, a German plant physiologist in 1930.[3] A high concentration of organic substances, particularly sugar, inside cells of the phloem at a source, such as a leaf, creates a diffusion gradient (osmotic gradient) that draws water into the cells from the adjacent xylem. This creates turgor pressure, also known as hydrostatic pressure, in the phloem. Movement of phloem sap occurs by bulk flow (mass flow) from sugar sources to sugar sinks. The movement in phloem is bidirectional, whereas, in xylem cells, it is unidirectional (upward). Because of this multi-directional flow, coupled with the fact that sap cannot move with ease between adjacent sieve-tubes, it is not unusual for sap in adjacent sieve-tubes to be flowing in opposite directions.
Answer:
Hlo mate..........
According to the Munch's Mass flow hypothesis, the turgor pressure makes the phloem sap to move from sugar sources to sugar sinks. Demerit: He does not account for different speeds of different substances and considered all the phloem as same.