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Xylem and Phloem
Concepts tested here
- Comparison of vessels and sieve tubes
All Questions
2006 AIPMT-PRE 1 question
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A common structural feature of vessel elements and sieve tube elements is -Vessel elements are the conducting cells of xylem. At maturity they are dead cells with thick lignified walls and no protoplast, so they have no nucleus.
Sieve tube elements are the conducting cells of phloem. They are living cells with thin cellulosic walls, but at maturity they lose their nucleus; their functions are controlled by the nucleus of the companion cells.
So both vessel elements and sieve tube elements are enucleate at maturity.
Thick secondary (lignified) walls are present only in vessel elements.
P-protein is present only in sieve tube elements.
Pits on the lateral walls are a feature of vessels, while sieve tubes have their pores mainly on the end walls (sieve plates).
So the common structural feature is the enucleate condition.