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The following are some statements about long distance translocation of photoassimilates in higher plants:
P. Sugars are translocated in the phloem by mass transfer along a hydrostatic pressure.
Q. The translocated carbohydrates are mostly non reducing sugars.
R. Munch- pressure flow hypothesis is crucial to drive translocation in the phloem.
S. Allocation and partition of carbon within a source leaf determine the phloem loading phenomenon.
Which one of the following combinations of the above statements is true?
P, Q and S
P, Q and R
P, R and S
P, Q, R and S.
Answers (1)
A high hydrostatic pressure is maintained in the phloem by the active uptake of sugar and other solutes. Due to hydrostatic pressure, pressure flow increases and the phloem sap starts moving.
The translocated carbohydrates are mostly non reducing sugars as non-reducing sugars can be easily transported, because they are less reactive.
The phloem sap (sucrose and other solutes in water) moves cell to cell along the concentration gradient. This is possible due to the development of the osmotically generated pressure gradient between source and sink. This pressure flow hypothesis, also known as the mass flow hypothesis, is the best-supported theory to explain the movement of sap through the phloem, given by Ernst Munch.
The partitioning and allocation of carbon (C) is intimately connected to plant growth since the export of carbohydrate from photosynthesizing leaves provides the substrate for the growth and maintenance of non-photosynthetic tissues.
Therefore, all the statements are correct. Hence, the correct answer is option 4.
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