Question

Assertion: Long-distance flow of photoassimilates in plants occurs through sieve tubes.
Reason: Mature sieve tubes have parietal cytoplasm and perforated sieve plates.

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

Answer 1

The correct option is A If both assertion and reason are true and the reason is a correct explanation of the assertion

Photoassimilates are the carbohydrates formed in the leaves of the plants by the process of photosynthesis. They are transported from the leaves to the other parts of the plants.

Phloem is a food conducting tissue formed of four different elements - sieve tube elements, companion cells, parenchyma and fibres.


Sieve tube elements are the main components that transport the material. It is a long, tube-like structure that has perforations in the end walls. During the process of maturation of the sieve tube elements, a series of progressive changes happen. They are devoid of the nucleus at maturity and are described as enucleated. They are associated with companion cells. Their cytoplasm is also located next to the cell wall and is known as parietal or peripheral cytoplasm. The clearing of the lumen and sieve plate pores make an ideal conduit for the flow of the solution of photoassimilates.