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Tracheids are dead cells with thick lignified walls that help in both mechanical support and water conduction.
Ref: NCERT Class 11 Biology Chapter 6: Anatomy of Flowering Plants Anatomy of Dicot and Monocot Stem
Origin of tracheids with lignified secondary walls solved two critical constraints for land colonization simultaneously. Hydraulically, they enabled efficient apoplastic water ascent under negative pressure generated by transpiration, sustaining tall aerial shoots despite absence of true roots initially assisted by capillary action and rhizoids. Mechanically, lignin confers compressive strength and resistance to collapse allowing upright growth, increased height, branching, improved light interception and canopy formation. This dual role in conduction and skeletal support facilitated evolution of complex sporophytes and Devonian forests.
Ref: Campbell Biology, Ch 29: Water transport evolution; Niklas Plant Biomechanics, lignin
The right choice is C: Tracheids. In BASICS of PLANT, that matches how the process or concept actually works — the other choices mix up related ideas or use the wrong mechanism. Skip these: A) Vessels; B) Sieve tubes; D) Companion cells. A quick check: if an option needs energy, pumps, or the opposite direction of movement, ask whether that really applies.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.
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