Part 3 — Anatomy of Stem: Primary Structure, Vascular Bundles, Cortex, Pith (Questions 51–75)

Q51. In dicot stem, the vascular bundles are:

A) Scattered and closed
B) Arranged in a ring and usually open (with cambium between xylem and phloem) — allows secondary growth
C) Absent
D) Only in leaves
Answer: B
Explanation:

B) Correct — dicot stem bundles: collateral open, ring-arranged.
A/C/D) False.

Q52. In monocot stem, vascular bundles are:

A) Ring arranged with active cambium
B) Scattered and usually closed (no cambium) resulting in lack of secondary thickening in most monocots
C) Concentric with phloem surrounding xylem only
D) Non-vascular
Answer: B
Explanation:

B) Correct — monocot bundles lack cambium and are scattered.
A/C/D) Incorrect.

Q53. A collateral vascular bundle is one in which:

A) Xylem and phloem are on the same side with phloem external to xylem (typical in stems)
B) Xylem surrounds phloem in ring
C) Phloem lies entirely interior to xylem
D) Xylem absent
Answer: A
Explanation:

A) Correct — collateral: phloem outside xylem.
B/C/D) Other arrangements (concentric) or false.

Q54. Bicollateral vascular bundle is:

A) Phloem on both outer and inner sides of xylem (as in cucurbits)
B) Xylem only
C) Phloem only
D) Found only in roots
Answer: A
Explanation:

A) Correct — bicollateral bundles have phloem on both sides.
B/C/D) Wrong.

Q55. Which statement about interfascicular cambium is correct?

A) It is formed from cortex cells only
B) It forms between vascular bundles when fascicular cambium joins with interfascicular meristem giving continuous cambial ring in dicot stems
C) Present only in monocots
D) Forms from epidermis
Answer: B
Explanation:

B) Correct — interfascicular cambium formation yields continuous cambium for secondary growth.
A/C/D) False.

Q56. The term open vascular bundle means:

A) Bundle has cambium and thus can undergo secondary growth
B) Bundle has no cambium
C) Bundle open to exterior
D) Bundle is dead
Answer: A
Explanation:

A) Correct — open bundle contains cambium between xylem & phloem.
B/C/D) Incorrect.

Q57. Primary cortex of stem often contains:

A) Chlorenchyma in herbaceous stems performing photosynthesis, collenchyma under epidermis for support, and parenchyma for storage
B) Xylem vessels only
C) Epidermis only
D) Vascular cambium only
Answer: A
Explanation:

A) Correct — cortex heterogeneous based on plant type.
B/C/D) Wrong.

Q58. Hypodermis in stems of many dicots is often:

A) Mechanical support layer, sometimes collenchymatous under epidermis especially in young stems (angular collenchyma)
B) Formed by xylem only
C) External protective cuticle only
D) Not present in any plant
Answer: A
Explanation:

A) Correct.
B/C/D) False.

Q59. Stem vascular bundles with xylem facing pith and phloem facing cortex are called:

A) Conjoint, collateral bundles
B) Radial bundles
C) Bicollateral bundles only
D) Separated bundles with phloem only
Answer: A
Explanation:

A) Correct — conjoint collateral bundles are common in stems.
B/C/D) Not matching.

Q60. The pith rays (medullary rays) function to:

A) Conduct water only upward
B) Radial transport of substances, storage and form parenchymatous rays in secondary xylem & phloem
C) Replace cambium
D) Produce stomata
Answer: B
Explanation:

B) Correct — rays transport radially and store materials.
A/C/D) Wrong.

Q61. Which tissue forms the bulk of woody stem (wood)?

A) Secondary phloem
B) Secondary xylem (wood) formed by activity of vascular cambium; heartwood & sapwood distinctions present
C) Epidermis
D) Cortex
Answer: B
Explanation:

B) Correct — secondary xylem constitutes wood.
A/C/D) Incorrect.

Q62. In dicot stem, vascular cambium arises from:

A) Only fascicular cambium of primary vascular bundles
B) Combination of fascicular cambium (from procambium) and interfascicular cambium (from parenchyma) forming a continuous ring
C) Cortex epidermis
D) Xylem vessels only
Answer: B
Explanation:

B) Correct — both sources give cambial ring for secondary growth.
A/C/D) Incomplete/wrong.

Q63. Medullary vascular bundles are:

A) Vascular bundles present in pith (as in monocots and some dicots)
B) Always absent in stems
C) Located in cortex only
D) Only in roots
Answer: A
Explanation:

A) Correct — medullary bundles are embedded in pith.
B/C/D) False.

Q64. In young dicot stem, the epidermis may be replaced during secondary growth by:

A) Lenticels only
B) Periderm (cork) formed by cork cambium (phellogen) replacing epidermis and cortex as bark forms
C) Xylem directly
D) Leaves
Answer: B
Explanation:

B) Correct — periderm replaces epidermis during secondary growth.
A/C/D) Not correct replacement.

Q65. Which cells commonly surround vascular bundles and may be sclerenchymatous providing mechanical strength?

A) Bundle sheath; e.g., in many dicots, sclerenchymatous bundle sheath or fibres protect bundles
B) Epidermis only
C) Root hairs
D) Guard cells
Answer: A
Explanation:

A) Correct — bundle sheath/fibres often sclerenchymatous.
B/C/D) Not related.

Q66. Which is true about monocot stem secondary growth?

A) Monocots generally lack vascular cambium and thus typical secondary growth, but some monocots (Dracaena, Yucca) show anomalous secondary thickening via secondary meristem or secondary thickening tissue
B) All monocots show normal secondary growth like dicots
C) Monocots have cambium in all species
D) Monocots have no growth at all after germination
Answer: A
Explanation:

A) Correct nuance.
B/C/D) False.

Q67. Vascular bundles in monocot stems are usually:

A) Closed and surrounded by sclerenchymatous bundle sheath (many have sclerenchymatous sheath)
B) Open with cambium always present
C) Formed from epidermis
D) Present only in leaves
Answer: A
Explanation:

A) Correct — monocot bundles usually closed and often have sclerenchymatous sheath.
B/C/D) False.

Q68. Which phrase describes a concentric vascular bundle?

A) Xylem entirely surrounding phloem (amphicribral/ampiphloic) or phloem surrounding xylem (amphivasal) — concentric arrangement
B) Xylem and phloem separated widely
C) No vascular tissues present
D) Only parenchyma present
Answer: A
Explanation:

A) Correct — concentric bundles have one element surrounding the other.
B/C/D) Wrong.

Q69. Collenchyma is typically found in stems at:

A) Vascular cambium only
B) Subepidermal region beneath epidermis, providing flexible mechanical support in young stems
C) Inside xylem only
D) Root cap only
Answer: B
Explanation:

B) Correct — angular/lamellar collenchyma supports young organs.
A/C/D) Incorrect.

Q70. The cylinder of sclerenchyma fibers forming a hard ring under epidermis in some stems is called:

A) Hypodermis or fiber cap supporting vascular bundles (e.g., in sunflower)
B) Xylem trachea
C) Pith parenchyma
D) Endodermis
Answer: A
Explanation:

A) Correct — fiber cap/hypodermal sclerenchyma provides rigidity.
B/C/D) Not this structure.

Q71. Which structure forms the leaf trace gap in a stem?

A) Where the vascular bundle supplying a leaf departs from central stele, the region left in stele is leaf trace gap (area where procambial continuity interrupted)
B) Always remains filled by xylem only
C) Epidermis forms gap
D) Root cap forms gap
Answer: A
Explanation:

A) Correct — leaf trace gaps are found above leaf traces in stem vascular system.
B/C/D) Not accurate.

Q72. Which of the following shows collateral closed vascular bundles?

A) Dicot stem (typically collateral open)
B) Monocot stem often has collateral closed bundle (no cambium)
C) Gymnosperm stem only
D) Woody dicot stem always
Answer: B
Explanation:

B) Correct — monocot bundles typically collateral closed.
A/C/D) Not generally.

Q73. Which vascular bundle type is typical of roots?

A) Conjoint collateral bundles scattered
B) Radial arrangement where xylem and phloem occur in alternating patches (radial bundles)
C) Concentric amphivasal only
D) No vascular bundles in roots
Answer: B
Explanation:

B) Correct — roots have radial organization with xylem/phloem alternating.
A/C/D) False.

Q74. Which best describes stele in stem?

A) Protostele, siphonostele, or eustele depending on plant group; dicot stems are eustele (discrete vascular bundles forming ring)
B) Only single type for all plants
C) Always hollow
D) Epidermal layer
Answer: A
Explanation:

A) Correct — stele varies across taxa: eustele typical of dicot stem.
B/C/D) Wrong.

Q75. The cambial initials are:

A) Cells of vascular cambium that divide to produce secondary xylem inward and secondary phloem outward — fusiform initials (axial) and ray initials (radial) comprising cambium
B) Epidermal cells only
C) Root hairs
D) Dead cells
Answer: A
Explanation:

A) Correct — cambial initials form secondary vascular tissues.
B/C/D) Not cambial initials.

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Part 3 — Anatomy of Stem: Primary Structure, Vascular Bundles, Cortex, Pith (Questions 51–75)