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  • Given below are statements describing various features of solute transport and photoassimilate translocation in plants. P. Apoplastic phloem loading of sucrose happens between cells with

Given below are statements describing various features of solute transport and photoassimilate translocation in plants.

P. Apoplastic phloem loading of sucrose happens between cells with no plasmodesmatal connections.

Q. Growing vegetative sinks (e.g. young leaves and roots) usually undergo symplastic phloem unloading.

R. Movement of water between phloem and xylem occurs only at the source and sink regions.

S. symplastic loading of sugars into the phloem occurs in the absence of plasmodesmatal connections.

Select the option that gives a combination of correct statements:

Option: 1

Only P and R

 


Option: 2

Only Q and R


Option: 3

Only Q and S


Option: 4

Only P and Q


Answers (1)

best_answer

R. Movement of water between the phloem and xylem occurs only at the source and sink regions.This statement is not accurate. The movement of water between the phloem and xylem can occur at various points along the transport pathway, not just limited to the source and sink regions. In the phloem, water moves through the process of translocation, which involves the movement of sugars and other solutes from source regions (such as leaves) to sink regions (such as growing tissues or storage organs). This movement of solutes creates a pressure gradient that drives the flow of water in the phloem. Water can move into the phloem from adjacent xylem vessels or from other cells connected to the phloem via plasmodesmata.

S. Symplastic loading of sugars into the phloem occurs in the absence of plasmodesmatal connections. This statement is also incorrect. Symplastic loading of sugars into the phloem occurs through plasmodesmata, which are channels that connect adjacent plant cells. Plasmodesmata allow for the movement of molecules, including sugars, between cells. In symplastic loading, sugars produced in the photosynthetic cells of the mesophyll (source tissues) are transported symplastically through plasmodesmata and into the companion cells and sieve elements of the phloem. From there, sugars can be further transported and distributed throughout the plant via the phloem sap.

In summary, both statements are inaccurate. Movement of water can occur between the phloem and xylem along the transport pathway, not just limited to source and sink regions. Additionally, symplastic loading of sugars into the phloem does occur through plasmodesmata. Hence, the correct answer is option 4. 

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