BPSC 70th CCE Re-exam Prelims General Studies · Question 94 of 142

Correct — B, Both at the base of leaves and tip of branches. A bud is a compressed, undeveloped shoot: a very short stem carrying a dome of meristematic tissue and a tight cluster of immature leaves, waiting to elongate. Plants place them in exactly two standard positions, and the question is built so that each of those positions is offered separately before the union of the two. The terminal or apical bud sits at the growing tip of the main stem and of every branch, and its meristem is what makes the shoot longer — primary growth. The axillary or lateral bud sits in the leaf axil, the angle between the upper surface of the leaf stalk and the stem, which is what 'at the base of leaves' describes; each leaf normally subtends one, and it is the reserve from which a new branch, or in due course a flower, develops. Because both positions are typical, options (a) and (c) are each true but incomplete, and the complete statement is their union. That structure is deliberate. When a paper offers X, Y and 'both X and Y', the union is correct whenever you can defend both halves separately — and here you can, since every twig you can pick up carries a bud at its tip and a bud in the angle of each leaf. Buds do occasionally appear elsewhere — adventitious buds form on roots and on leaf margins, as in Bryophyllum — but those are the exception, and the word 'typically' in the stem excludes them.

• (a)At the base of leaves — True but only half of the answer. This describes the axillary bud, which lies in the leaf axil where the petiole meets the stem, and it is the correct position for the buds that become branches. It leaves out the terminal bud at the growing tip, which is the more important of the two because it drives the elongation of the shoot and, through apical dominance, controls whether the axillary buds are allowed to grow at all.
• (c)At the tip of branches — Also true and also incomplete. This is the terminal or apical bud, one per stem and one per branch. Taking it alone leaves out the far more numerous axillary buds — a plant carries one at nearly every node — and it would make branching impossible to explain, since a new branch has to start from a bud that is not at the tip.
• (d)None of the above — A 'none of the above' option is correct only if you can show that each of the other three fails, and here one of them is fully correct. Since (b) states both standard positions and both are right, (d) is dead. It is worth applying that test explicitly on this paper, where the option is offered very often and functions mostly as a distractor for candidates who are unsure rather than as a genuine answer.

A bud is best understood as a shoot in miniature, packed and paused. It has a shoot apical meristem, the ring of dividing cells that produces all the stem and leaf tissue above it, wrapped in leaf primordia and often protected by scale leaves in the perennating buds of temperate trees. Buds are classified in three ways at once. By position: terminal or apical at the tip; axillary or lateral in the leaf axil; accessory where more than one sits at the same node; adventitious where a bud arises outside these positions altogether, on a root or a leaf margin. By contents: vegetative buds produce leaves and stem, floral buds produce flowers, mixed buds produce both. By activity: active or dormant, the latter waiting on a season or on the removal of some restraint. The restraint is usually apical dominance — auxin produced by the apical bud travels down the stem and suppresses the axillary buds below it, which is why an unpruned plant grows tall and spindly and a pruned one grows bushy. Remove the tip and you remove the source of the auxin, and the axillary buds break; that single fact is the basis of pruning, hedging, pinching in floriculture, and the plucking of tea.

Two ideas turn this from a memory question into a reasoned one. The first is the 'both' structure: whenever a paper offers two partial statements and their union, test each half on its own, and take the union if both survive. The second is that buds explain what would otherwise be a puzzle — how a plant that keeps growing from its tip ever produces a side branch. The answer is that the axillary bud is a stored, complete shoot apex, held in reserve at every node. The same reserve is what makes vegetative propagation possible, and this is where the topic touches agriculture directly. A sugarcane crop is planted from setts, short lengths of cane each carrying at least one bud at a node; a potato is planted from a tuber whose 'eyes' are axillary buds on a modified underground stem, which is why the potato counts as a stem and not a root; a grape vine or a bougainvillea is raised from a stem cutting that roots at the base and shoots from the buds above. Every one of these depends on the fact this question is testing, which is that a stem carries dormant shoot apices at its nodes.

• A bud is a compressed, undeveloped shoot consisting of a shoot apical meristem with leaf primordia; the terminal (apical) bud occupies the tip of the stem and of each branch.
• An axillary (lateral) bud lies in the leaf axil — the angle between the petiole and the stem — and normally one is present at each node; it is the origin of every side branch.
• Apical dominance: auxin produced at the apical bud moves downward and suppresses the axillary buds, so removing the tip by pruning or pinching makes the plant branch.
• Adventitious buds arise outside these positions — on roots, or along leaf margins as in Bryophyllum — and are the exception the stem's word 'typically' excludes.
• The 'eyes' of a potato are axillary buds on an underground stem tuber, which is why a potato is classed as a modified stem while a carrot and a sweet potato are modified roots.

• Stopping at the first true option. Both (a) and (c) are correct as far as they go; the question is testing whether you notice that neither is complete.
• Choosing 'None of the above' out of doubt. It is correct only when all three of the others can be shown to fail, and here one of them is fully right.
• Treating adventitious buds as the norm. Buds on leaf margins and roots exist, but the stem says 'typically', which points to the terminal and axillary positions.

BPSC sets school-level biology as a bare definition and then hides the difficulty in the option set rather than in the fact — here by splitting one correct answer into two partial ones and adding an escape option. UPSC does not ask where buds are; it asks what depends on them, as in its questions on which plants can be raised from stem cuttings and on which vegetable is a modified stem, so the same fact has to be held in an applied form.

• practice — not a real PYQ

  The removal of the apical bud of a plant results in

  • (a)Suppression of the growth of lateral buds
  • (b)Growth of the lateral buds and increased branching
  • (c)Immediate flowering of the plant
  • (d)Death of the whole shoot system

  Answer(b) Growth of the lateral buds and increased branching — the apical bud supplies the auxin that enforces apical dominance, so removing it releases the axillary buds. This is the principle behind pruning, hedging and pinching.

• practice — not a real PYQ

  The 'eyes' of a potato are

  • (a)Adventitious roots
  • (b)Axillary buds
  • (c)Modified leaves
  • (d)Lenticels for gas exchange

  Answer(b) Axillary buds — they sit at the nodes of an underground stem tuber, which is the reason a potato is classified as a modified stem while a carrot and a sweet potato are modified roots.