Question

Assertion : The direction of movement of organic solutes in the phloem is bi-directional.
Reason : The transportation depends on variability of source-sink relationship.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (A)

Phloem transport is the long distance movement of organic substances from the source or supply end (region of manufacture or storage) to the region of utilisation or sink. But the source and sink may be reversed depending on the season or need of the plants. Sugar stored in roots may be mobilised to become a source of food in the early spring when the buds of trees act as sink and require energy for their growth and development. Since the source- sink relationship is variable, the direction of movement of organic solutes in phloem can be upwards or downwards i.e., bidirectional.