CDS (I) 2023 General Knowledge · Question 42 of 120

Correct — C, base of leaves. Intercalary meristem is the dividing tissue that sits between regions of permanent tissue rather than at a growing tip. In monocots, and in grasses above all, it is found at the base of the nodes and at the base of the leaf blades — as the standard description puts it, intercalary meristems 'occur in monocot (in particular, grass) stems at the base of nodes and leaf blades'. That position explains the most familiar fact about grass. A lawn cut with a mower, or a pasture cropped by cattle, loses the tip of every blade, and grass survives that treatment because the growing zone is at the bottom of the leaf and not at the top. The tissue at the base pushes fresh blade upward, so 'damaged leaves rapidly regrow'; this leaf regrowth in grasses evolved in response to damage by grazing herbivores and fire. Cut the top off a shoot with an apical meristem and growth in length stops; cut the top off a grass leaf and it comes back. UPSC's own key for the CDS paper of 2021 gives the same location in almost the same words — 'base of the leaves or internodes'.

• (a)root tip — That is apical meristem, at the growing point of the root. It drives the root's growth in length, and it is not intercalary because nothing lies beyond it.
• (b)lateral sides of stem — That is lateral meristem — the cambium — which adds to a plant's girth rather than its length. Grasses, being monocots, mostly lack the secondary growth it produces.
• (d)shoot tip — Apical meristem again, this time of the shoot. Damage to it stops the plant growing taller, which is exactly the vulnerability that the intercalary arrangement in grasses avoids.

Plant growth comes from meristems, tissues whose cells keep dividing. NCERT's Class 11 text classifies them as apical, lateral and intercalary. Apical meristems sit at the tips of roots and shoots and produce growth in length. Lateral meristems, the cambia, run along the sides and produce growth in girth. Intercalary meristems are left behind by the apical meristem at the base of internodes or leaves and go on dividing there, which allows a plant to lengthen a segment that is no longer at a tip.

This is a locate-the-tissue question, and the useful discipline is to name what each wrong option actually describes rather than merely reject it. Root tip and shoot tip are both apical; the sides of the stem are lateral; only the base of the leaf is left, and that is the intercalary position. The reason to remember it through grass rather than through the definition is that the biology and the agriculture line up: the meristem's position at the base of the blade is why a lawn can be mown weekly, why a paddy field regrows after grazing, and why fodder grasses can be cut several times in a season.

• Intercalary meristem occurs at the base of nodes and leaf blades in monocot, and especially grass, stems.
• NCERT Class 11 Biology classifies plant meristems as apical, lateral and intercalary.
• Apical meristem sits at the tips of roots and shoots and produces primary growth in length.
• Lateral meristem, the cambium, produces secondary growth in girth and is largely absent in monocots.
• The intercalary position lets a grass leaf regrow after its tip is removed, an adaptation to grazing and to fire.

• Reading any actively dividing tissue as apical; position is what defines the three types.
• Assuming grasses grow from the tip like a tree shoot, which would make mowing fatal.
• Confusing intercalary meristem with the intercalary growth of an internode after the meristem has ceased dividing.

As a location item on one of the three meristems, or as a which-tissue item on growth in length against growth in girth.

• practice — not a real PYQ

  Growth in the girth of a plant stem results from division of cells in which one of the following?

  • (a)Apical meristem
  • (b)Lateral meristem
  • (c)Intercalary meristem
  • (d)Permanent tissue

  Answer(b) Lateral meristem — the cambium, which produces secondary growth; apical and intercalary meristems add length rather than girth.

• practice — not a real PYQ

  Grass survives regular mowing chiefly because of which one of the following?

  • (a)Its leaves have no growing tissue at all
  • (b)Its growing tissue lies at the base of the leaf rather than at the tip
  • (c)It regrows from the root cap after cutting
  • (d)Its stem cambium replaces the cut leaves

  Answer(b) Its growing tissue lies at the base of the leaf rather than at the tip — the intercalary meristem, which is why removing the tip does not stop the blade from lengthening.