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Which statement about mature sieve-tube cells is correct?
AThey keep a nucleus and rely on no other cell
BThey die at maturity and their walls lignify
CThey lose the nucleus yet remain alive at maturity
DThey divide repeatedly to renew the sieve tube
Answer & Solution
Correct answer: C. They lose the nucleus yet remain alive at maturity
1. Sieve-tube cells sit end to end to build a long sieve tube that carries sugars and amino acids.
2. Sugar flows between them through perforated sieve plates at the junctions.
3. These cells are still alive at maturity, but the nucleus and other cell components have disintegrated.
4. So a sieve-tube cell cannot be described as keeping its nucleus, which rules out the first option.
5. Dying and lignifying describes xylem conducting cells, which is the trap for a reader who confuses the two tissues.
6. Companion cells supply the metabolic support that the stripped down sieve-tube cell can no longer provide, and no repeated division renews the tube.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 30 "Plant Form and Physiology", section 30.2 Stems_
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