Q.17 Given below are two statements, one is labelled as Assertion (A) and other one
labelled as Reason (R).
Assertion (A) : Root apical cell theory of Nageli does not hold good for flowering
plants
Reason (R) : In flowering plants, a group of initials has been observed
In light of the above statements, choose the correct answer from the options given
below.
1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
3. (A) is true but (R) is false.
4. (A) is false but (R) is true.
Root Apical Cell Theory Nageli: Assertion-Reason
Nageli’s root apical cell theory proposes a single tetrahedral apical initial cell drives root growth, mainly observed in vascular cryptogams like ferns. In flowering plants (angiosperms), root apical meristems instead feature a group of initials, making the theory inapplicable.
Assertion (A): Root apical cell theory of Nageli does not hold good for flowering plants.
Reason (R): In flowering plants, a group of initials has been observed.
Correct Answer: Option 1
Both (A) and (R) are true, and (R) correctly explains (A). Flowering plants lack a single apical cell; their root apices have multiple initial cells (e.g., in quiescent center models), directly accounting for why Nageli’s theory fails here.
Detailed Explanation of All Options
Option 1: Both True, (R) Explains (A) ✅ Correct
Nageli’s theory suits pteridophytes with one tetrahedral cell dividing into root cap, epidermis, cortex, and stele. Angiosperms use a group of initials (protoderm, ground meristem, procambium initials), validating both statements with causal link.
Option 2: Both True, (R) Not Explanation
Incorrect—(R) precisely justifies (A), as the “group of initials” replaces the single cell in angiosperm root apices (e.g., maize, pea roots).
Option 3: (A) True, (R) False
Wrong—(R) is factual; modern views confirm initials groups in flowering plant root meristems, not solitary cells.
Option 4: (A) False, (R) True
Invalid—(A) holds; theory doesn’t apply to seed plants like angiosperms, confirmed by histogen and Korper-Kappe theories.
| Option | (A) Status | (R) Status | Explanation Matches? | Why? |
|---|---|---|---|---|
| 1 | True | True | Yes | Group of initials causes theory failure |
| 2 | True | True | No | But (R) directly explains |
| 3 | True | False | – | (R) is true in angiosperms |
| 4 | False | True | – | (A) is true; single cell absent |
Exam Tips: Master Apical Meristem Theories
-
Nageli vs. Modern: Single cell (cryptogams) → Group initials/quiescent center (angiosperms).
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Compare theories: Histogen (3 layers), Korper-Kappe (body-cap).
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NEET high-yield: Link to root zones (calyptrogen, dermatogen, periblem, plerome).
Practice similar assertion-reason on “root apical cell theory Nageli” for botany dominance!
