Q.46 Bast fibres are present in
(A) Xylem (B) Phloem (C) Collenchyma (D) Parenchyma
Bast Fibres Location in Plants: Phloem, Xylem, Collenchyma or Parenchyma?
Bast fibres, also called phloem fibres, provide mechanical support in dicot stems and are commercially important (jute, flax, hemp). They strengthen the vascular system while allowing nutrient transport. These long sclerenchyma cells occur specifically in one tissue type.
Correct Answer
(B) Phloem. Bast fibres are phloem fibres found in the inner bark (bast) of dicot stems, supporting sieve tubes and companion cells.
Bast Fibre Characteristics
Bast fibres are elongated sclerenchyma cells with thick lignified walls and tapered ends. They form bundles in secondary phloem, running longitudinally through stems. Extracted via retting, they yield strong textiles and ropes.
Tissue Functions
Phloem conducts sugars downward; bast fibres reinforce it mechanically. Xylem handles water transport with its own fibres. Collenchyma and parenchyma provide flexible support or storage but lack true bast fibres.
Option Analysis
| Option | Tissue | Correctness | Reason |
|---|---|---|---|
| (A) | Xylem | Wrong | Contains libriform fibres and tracheids for water conduction/support; not called “bast” (phloem-specific term). |
| (B) | Phloem | Correct | Bast = phloem fibres in inner bark; supports conductive elements in dicots like jute . |
| (C) | Collenchyma | Wrong | Living cells with pectin-thickened corners for flexible support under epidermis; no lignified bast bundles. |
| (D) | Parenchyma | Wrong | Thin-walled, living cells for storage/photosynthesis; lacks sclerenchymatous bast fibre structure. |
Exam Tips
Remember: “Bast” derives from “bark/phloem.” Commercial fibres (jute=Corchorus phloem) distinguish from xylem fibres. Secondary growth produces bast in dicots; monocots lack them.
