Q.26 Vascular bundle, in which the primary xylem is bounded both to the inside and outside by strands of primary
phloem, is known as:
I. Collateral bundle
2. Bicollateral bundle
3. Amphivasal bundles
4. Amphicribral bundles
Bicollateral bundles have primary phloem strands on both sides of primary xylem, typical in Cucurbitaceae stems.
The correct answer is 2. Bicollateral bundle.
Question Breakdown
This MCQ tests vascular bundle classification based on xylem-phloem arrangement in dicot stems, key for NEET anatomy.
Option Explanations
| Option | Bundle Type | Arrangement | Example [Citation] |
|---|---|---|---|
| 1 | Collateral | Phloem outside xylem only (one side) | Dicot stems (sunflower) |
| 2 | Bicollateral | Phloem strands both outside AND inside xylem | Cucurbita, Cucumis |
| 3 | Amphivasal | Xylem surrounds phloem (xylem outside) | Dracaena, Yucca |
| 4 | Amphicribral | Phloem surrounds xylem (phloem outside) | Ferns, Selaginella |
Key Distinction
-
Collateral: Phloem → Xylem (one phloem patch)
-
Bicollateral: Phloem → Xylem → Phloem (two phloem patches sandwiching xylem)
Article Introduction
Master vascular bundle in which primary xylem is bounded both to inside and outside by strands of primary phloem—bicollateral bundle (option 2)—crucial for NEET/CUET plant anatomy. This guide differentiates bicollateral from collateral/amphivasal/amphicribral bundles, explains Cucurbitaceae stem structure, and clarifies xylem-phloem arrangements for exam success.
Bundle Types Diagrammed
Collateral: Phloem | Xylem
Bicollateral: Phloem | Xylem | Phloem
Amphivasal: Xylem | Phloem | Xylem
Amphicribral: Phloem | Xylem | Phloem (complete surround)
Occurrence & Function
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Bicollateral: Open bundles (2 cambium strips); secondary growth on both sides; Cucurbitaceae family.
-
Enables bidirectional secondary thickening unlike typical collateral bundles.
Exam Strategy
Remember: “Bi-” = two phloem sides around xylem. Cucurbita = bicollateral classic example.
