Q.What would be expected to happen if:

(a) GA3 applied to rice seedlings: gibberellins increase the length of the axis, so the seedlings would grow excessively tall and thin (elongated), resembling the 'bakanae' or foolish-seedling condition. (b) Dividing cells stop differentiating: without differentiation the cells would not mature into specialised tissues, so no proper structures/organs would form and normal development would not take place (only an undifferentiated mass of cells). (c) A rotten fruit mixed with unripe fruits: the rotten fruit releases ethylene, which promotes ripening, so the surrounding unripe fruits would ripen quickly. (d) Forgetting to add cytokinin to the culture medium: cytokinins are essential for cytokinesis (cell division); without them the cells in culture would not divide (or divide poorly), …

1. If GA3 is applied to rice seedlings Gibberellins, and especially gibberellic acid (GA3), cause an increase in the length of the plant axis. Applying GA3 to rice seedlings would therefore make them grow abnormally tall, spindly and elongated. This is exactly the effect seen in the 'bakanae' or foolish seedling disease, in which the fungus Gibberella fujikuroi produces gibberellins that make rice seedlings excessively tall.
2. If dividing cells stop differentiating Differentiation is the process by which cells derived from meristems mature to perform specific functions (for example forming tracheary elements). If dividing cells stop differentiating, they would keep dividing but never mature into specialised cells, tissues or organs. The result would be an undifferentiated mass of cells (like a callus) and a failure of normal development, since development is the sum of growth and differentiation.
3. If a rotten fruit gets mixed with unripe fruits Ripening and rotting fruits synthesise large amounts of the gaseous hormone ethylene, which is highly effective in fruit ripening and enhances respiration during ripening. The ethylene given off by the rotten fruit would diffuse to the neighbouring fruits and cause the unripe fruits to ripen rapidly — the basis of the saying that one rotten fruit spoils the whole basket. …

Method: Predicting the Outcome of a Hormonal or Developmental Change

For 'what would happen if...' questions, first name the exact process or hormone involved, then apply its one well-known effect in the direction implied by the scenario.

Steps

Step 1: Identify which single hormone or process the scenario is really testing.

'GA3 applied' → gibberellin's elongation effect. 'Cells stop differentiating' → loss of the maturation step of development. 'Rotten fruit nearby' → ethylene release. 'No cytokinin in culture' → loss of the cell-division signal.

Step 2: State that hormone or process's normal, well-established effect. …