Given below are two statements:
Statement (I): The direction of movement of water and nutrients in xylem and phloem is unidirectional
Statement (II): Sucrose is transported from the source to the sink via phloem
In light of the above statements, choose the most appropriate answer from the options given below.
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Xylem transport is driven by passive transpiration pull (unidirectional), while phloem transport is an active, energy-requiring process driven by turgor pressure gradients from source to sink (multidirectional).
Statement (I) is true but Statement (II) is false.
Statement (I) is false but Statement (II) is true.
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The Correct Option isD
Solution and Explanation
Step 1: Understanding the Concept:
Plants have two specialized vascular tissues for long-distance transport: xylem (which transports water and minerals) and phloem (which transports organic photosynthates). The directions of transport in these two systems differ. Step 2: Detailed Explanation:
Let us analyze both statements:
Statement (I): Water and mineral transport in the xylem is strictlyunidirectional, moving upwards from the roots to the stems, leaves, and transpirational surfaces.
However, the transport of organic solutes (sugars) in the phloem ismultidirectional (bidirectional).
Organic food can flow upwards or downwards depending on where the source (photosynthesizing leaves) and the sink (roots, storage organs, developing buds, or fruits) are located.
Since the statement claims transport in both xylem and phloem is unidirectional, Statement (I) isfalse.
Statement (II): Sucrose is the primary transport sugar in plants because it is highly soluble, stable, and non-reducing.
According to the pressure-flow (mass-flow) hypothesis, sucrose is loaded into the phloem sieve tubes at the source (leaves) and translocated to various sink tissues (roots, fruits) where it is unloaded and utilized. Thus, Statement (II) istrue.
Therefore, Statement (I) is false but Statement (II) is true. Step 2: Final Answer:
The correct option is (D).
