Which one of the following regions in plants is responsible for the growth of its roots and shoots?

Correct — D, Apical meristem. Growth in length at both ends of the plant body comes from apical meristem — the dividing tissue at the tip of the root and the tip of the shoot. Its cells are small, thin-walled, densely cytoplasmic, without large vacuoles, and they divide repeatedly; the cells left behind then elongate and differentiate into permanent tissue. This lengthwise growth is called primary growth, and it is distinct from the increase in girth produced by lateral meristem such as the vascular cambium.

• (a)Collenchyma — A simple permanent tissue, not a meristem. Its cells have stopped dividing; their thickened corners give a young stem flexibility, but they add no new cells.
• (b)Endodermis — The innermost layer of the cortex, marked by the Casparian strip. It regulates which water and solutes may pass into the stele — a gatekeeping role, not a growth one.
• (c)Cortex — The ground tissue between epidermis and vascular cylinder, largely parenchyma. It stores food and gives bulk to the young root or stem, but it is permanent tissue and does not drive elongation.

Plant growth is localised in meristems, tissues whose cells retain the power to divide. Apical meristems at root and shoot tips produce primary growth, the increase in length. Intercalary meristems, found at the bases of leaves or above the nodes in grasses, let a grazed or mown grass blade regrow from below. Lateral meristems — the vascular cambium and cork cambium — produce secondary growth, the increase in girth, and are what make a tree trunk thicken year after year.

Only one of the four options is a meristem at all; the rest are permanent tissues or regions of the root. The quickest route through the item is therefore to ask which name belongs to dividing tissue rather than to try to recall the function of each. If a similar question offers both apical and intercalary meristem, read the stem for the word 'tip' or the words 'roots and shoots' — those point to the apical meristem, while regrowth of grass after mowing points to the intercalary one.

• Apical meristem sits at the tips of roots and shoots and produces growth in length.
• Lateral meristem — vascular cambium and cork cambium — produces growth in girth.
• Intercalary meristem lies at the base of leaves or above the nodes and lets grasses regrow after grazing.
• Meristematic cells are small, thin-walled and densely cytoplasmic, with no large vacuole.
• The endodermis is marked by the Casparian strip and controls entry into the vascular cylinder.

• Picking a permanent tissue because its name is familiar from the same chapter.
• Confusing apical with lateral meristem — length comes from apical, girth from lateral.
• Assuming the root cap is the dividing region; it is a protective cover over the meristem behind it.

Straight recall with three permanent tissues used as decoys — the exam is checking whether meristem and permanent tissue are kept separate.

• practice — not a real PYQ

  Growth in the girth of a tree trunk is brought about mainly by

  • (a)apical meristem
  • (b)intercalary meristem
  • (c)lateral meristem
  • (d)the root cap

  Answer(c) lateral meristem — the vascular cambium and cork cambium add cells sideways, producing secondary growth.

• practice — not a real PYQ

  In grasses, the meristem that allows a mown leaf to grow back is located at the

  • (a)shoot tip
  • (b)root tip
  • (c)base of the leaf
  • (d)leaf margin

  Answer(c) base of the leaf — this intercalary meristem survives cutting and pushes the blade up again.