Q.41 Given below are two statements: one is labelled as Assertion-A and the other is labelled as Reason-R

Assertion-A: Regions of active cell division are responsible for the increase in the length of roots and stems

Reason-R: Growth is an irreversible increase in volume or size

In the 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

   Assertion A is false, while Reason R is true. Regions of active cell division contribute to growth but do not solely drive length increases in roots and stems, which primarily result from cell elongation.

   Question Analysis

   This assertion-reason question evaluates plant growth mechanisms. Active division occurs in meristems, but longitudinal growth depends mainly on elongation posterior to these regions.

   Option Breakdown

   • Both A and R true, R explains A: Incorrect. R defines growth accurately (irreversible size increase via division/expansion), but A wrongly attributes length growth solely to division regions.​

   • Both A and R true, R does not explain A: Incorrect. A is false—apical meristems produce new cells, but elongation zones (e.g., behind root tip) cause 90%+ length increase.​

   • A true, R false: Incorrect. R is the standard biological definition of growth; A fails as stated.​

   • A false, R true: Correct. Division initiates growth, but irreversible expansion drives dimension changes.

   Correct Answer: A is false but R is true.

   Regions of active cell division roots stems (meristems) produce cells for growth, but length increases via elongation, not division alone. This distinction clarifies assertion-reason questions in plant physiology.​

   Growth Zones

   Apical meristems divide rapidly; sub-apical regions elongate irreversibly via vacuolation and wall loosening (auxin-driven). Roots elongate 95% behind meristem; stems similar.​

   Option	Validity	Explanation
   Both true, R explains A	False	A incorrect ​
   Both true, R not explain	False	A false ​
   A true, R false	False	R defines growth ​
   A false, R true	True	Elongation primary ​

   Exam Insight

   R matches NCERT growth definition. A misstates primary length mechanism—key for CSIR-NET/NEET. Meristems add cells; expansion adds size.​