Q56 Periderm is a protective tissue found in stems and roots of gymnosperm and woody dicotyledons. It contributes to the increased thickness by secondary growth. Match the periderm components given in Group I with the cell tissue in Group II.
| Group I | Group II |
|---|---|
| (P) Phelloids | (1) Tissue resembling cortical parenchyma |
| (Q) Phellogen | (2) Cork cambium |
| (R) Phelloderm | (3) Cork-like cells |
| (S) Periderm | (4) Cork cells |
| (A) | P-4; Q-3; R-1; S-2 |
| (B) | P-3; Q-2; R-4; S-1 |
| (C) | P-2; Q-1; R-3; S-4 |
| (D) | Q-1; R-3; S-2 |
Periderm in gymnosperms consists of phellogen (cork cambium), phellem (cork), and phelloderm (secondary cortex), which collectively replace the epidermis during secondary growth to protect stems and roots. The correct matching for Group I (periderm components) to Group II (their descriptions) is option (B) P-3, Q-2, R-5, S-1. This aligns with standard botany for CSIR NET Life Sciences preparation.
Question Breakdown
The query matches standard periderm components from Group I to Group II descriptions:
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Group I: (P) Phelloids, (Q) Phellogen, (R) Phellem, (S) Phelloderm.
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Group II: (1) Tissue resembling cortical parenchyma, (2) Cork cambium, (3) Cork-like, (4) Cork, (5) Parenchyma cells.
Phelloids refer to parenchyma-like cells in the phelloderm layer, resembling cortical parenchyma. Phellogen is the meristematic cork cambium that divides to produce outer phellem and inner phelloderm. Phellem forms dead, suberized cork-like cells for protection. Phelloderm consists of living parenchyma cells.
Option Analysis
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(A) P-4, Q-3, R-1, S-2: Incorrect. Mismatches phelloids (P) to cork (4), phellogen (Q) to cork-like (3), and phelloderm (S) to cork cambium (2).
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(B) P-3, Q-2, R-5, S-1: Correct. Phelloids (P) match parenchyma cells (5); phellogen (Q) is cork cambium (2); phellem (R) is cork-like (3); phelloderm (S) resembles cortical parenchyma (1).
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(C) P-2, Q-1, R-3, S-4: Incorrect. Assigns phelloids (P) to cork cambium (2) and phelloderm (S) to cork (4), ignoring their living parenchyma nature.
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(D) Q-1, R-3, S-2: Incomplete, ignores phelloids (P) and mismatches phellogen (Q) to parenchyma-like tissue.
Periderm structure in gymnosperms plays a key role in secondary growth, replacing the epidermis in stems and roots as they thicken. This protective tissue comprises phellogen, phellem, and phelloderm, essential for CSIR NET Life Sciences aspirants tackling matching questions on periderm components.
Periderm Components Explained
Phellogen, or cork cambium, is the lateral meristem that produces phellem outward (suberized cork cells) and phelloderm inward (living parenchyma). In gymnosperms, it arises from cortex or phloem, forming successive layers for protection against pathogens and water loss. Phelloids are specialized parenchyma cells within phelloderm, resembling cortical tissue.
Secondary Growth Role
Secondary growth in gymnosperms involves vascular cambium for xylem/phloem and phellogen for periderm, increasing girth while maintaining bark integrity. Unlike dicots, gymnosperm periderm often forms discontinuous bands enclosing phloem.
CSIR NET Matching Tips
For questions matching phellogen to “cork cambium,” phellem to “cork-like,” phelloderm to “cortical parenchyma,” and phelloids to “parenchyma cells,” select sequences like P-3, Q-2, R-5, S-1. Practice diagrams of periderm layers for visual recall.
