NDA (II) 2021 General Ability Test · Question 111 of 149

Correct — B, lateral meristem only. Girth means the thickness of the stem, and an increase in thickness is secondary growth. Secondary growth is produced by the lateral meristems, chiefly the vascular cambium and the cork cambium, which add new cells sideways and so widen the stem. The apical meristem only makes the plant longer, so girth increases due to the lateral meristem alone.

• (a)apical meristem only. — The apical meristem lies at the tips of roots and shoots and adds length (primary growth); it does not increase the thickness or girth of the stem.
• (c)apical and intercalary meristem. — Both apical and intercalary meristems add to length, the intercalary being found at the base of internodes in grasses; neither increases girth.
• (d)both apical and lateral meristem. — Only the lateral meristem widens the stem; adding the apical meristem is wrong because it contributes to length, not thickness.

Meristems are regions of dividing cells that drive plant growth. Apical meristems at root and shoot tips cause primary growth, making the plant taller and longer. Lateral meristems, the vascular cambium and cork cambium, cause secondary growth, adding cells sideways to increase the girth of stems and roots. Intercalary meristems, at internode bases, also add length.

The deciding word is 'girth', meaning thickness. Length comes from apical (and intercalary) meristems, while thickness comes from lateral meristems. So an increase in girth must be credited to the lateral meristem only.

• Girth is the thickness of the stem; increasing it is secondary growth.
• Lateral meristems (vascular cambium and cork cambium) increase girth.
• Apical meristems at root and shoot tips increase length (primary growth).
• Intercalary meristems at internode bases also add to length, mainly in grasses.

• Crediting the apical meristem for thickness when it only adds length.
• Choosing a combined option that includes the apical meristem for an increase in girth.

Asked as which meristem increases the girth or thickness of a stem; the answer is the lateral meristem (cambium), responsible for secondary growth.

No directly related past PYQ was found.

• practice — not a real PYQ

  Increase in the length of a plant is brought about mainly by the

  • (a)lateral meristem
  • (b)apical meristem
  • (c)cork cambium
  • (d)vascular cambium

  Answer(b) apical meristem — located at root and shoot tips, it drives primary (length) growth.

• practice — not a real PYQ

  The vascular cambium in a woody stem is an example of

  • (a)apical meristem
  • (b)intercalary meristem
  • (c)lateral meristem
  • (d)permanent tissue

  Answer(c) lateral meristem — it adds cells sideways to increase girth.