Which of the following best represents the cells of a meristem of plant?

Correct — A, Dense cytoplasm, thin cell wall, large nuclei and absence of vacuoles. A meristem is a tissue whose cells are actively dividing, and every feature in that description follows from division. The cells are small and packed with cytoplasm because they are constantly building new material; their walls are thin primary walls of cellulose, since a thick wall would prevent further division; their nuclei are large in proportion to the cell because the DNA is repeatedly being copied; and they have few or no vacuoles, because a large water-filled vacuole is something a cell acquires later, as it enlarges and matures. Meristematic cells also sit tightly packed with no intercellular spaces.

• (b)Dense cytoplasm, thin cell wall, large nuclei and large vacuoles — Correct on the first three counts and wrong on the last. A large central vacuole is the hallmark of a mature permanent cell, not of a dividing one.
• (c)Dense cytoplasm, thin cell wall, small nuclei and absence of vacuoles — Shrinks the nucleus. In a meristematic cell the nucleus is prominent and occupies a large share of the small cell's volume.
• (d)Dense cytoplasm, thick cell wall, small nuclei and large vacuoles — Describes a mature permanent cell such as sclerenchyma — thick-walled, vacuolated and no longer dividing. It reverses three of the four features at once.

Plant tissues are either meristematic or permanent. Meristematic tissue retains the power of division and is the source of all growth; permanent tissue is what meristematic cells become once they stop dividing and differentiate. By position there are three meristems — apical, at root and shoot tips, which lengthens the plant; intercalary, at the base of leaves or internodes and prominent in grasses; and lateral or cambium, which increases girth.

Every option here begins with 'dense cytoplasm', so that word carries no information and the answer turns on the last three features. The most reliable way through is to reason from function rather than to recall a list. A cell about to divide must be able to expand its wall, so the wall stays thin; it must copy and manage a great deal of DNA, so the nucleus is large; and it cannot afford to hand over most of its volume to a vacuole of water, so vacuoles are absent or tiny. Reverse each of those and you have described a mature cell, which is precisely what option (d) does. Cutting the apical meristem off a shoot stops the plant growing taller, which is the basis of pruning and of hedging.

• Meristematic cells are small, thin-walled and densely cytoplasmic, with large nuclei and few or no vacuoles.
• They are tightly packed with no intercellular spaces.
• Apical meristem at root and shoot tips increases length; lateral meristem or cambium increases girth; intercalary meristem lies at the base of leaves or internodes.
• Vacuolation and wall thickening happen during differentiation, as a meristematic cell becomes a permanent cell.
• Removing the apical meristem stops growth in length, which is why pruning encourages a bushier plant.

• Attaching a large vacuole to a dividing cell; the vacuole belongs to the mature stage.
• Reading 'dense cytoplasm' as the distinguishing feature when every option carries it.
• Thinking of meristem cells as large because they produce a large plant — they are among the smallest cells in it.

Asked as a four-feature description in which the options differ by only one or two attributes, so each attribute has to be checked separately.

• practice — not a real PYQ

  Increase in the girth of a stem is brought about by

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

  Answer(b) lateral meristem — the cambium, which adds cells sideways; apical meristem adds length instead.

• practice — not a real PYQ

  Which one of the following is a characteristic of permanent tissue in plants?

  • (a)Continuous cell division
  • (b)Absence of vacuoles
  • (c)Loss of the ability to divide
  • (d)Very large nuclei

  Answer(c) Loss of the ability to divide — permanent tissue is what meristematic tissue becomes after differentiation.