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Q. The following experiment was performed to test the effect of auxin on the plant growth. Five plant seedlings (all growing actively) were prepared as below; they were unilaterally illuminated, and growth was measured after 10 days.
Treatments :
Plant A: Tip not removed, nothing applied
Plant B: Tip removed, nothing applied
Plant C: Tip removed, gelatin block with cytokinin was placed on the cut edge
Plant D: Tip removed gelatin block with auxin placed on the cut edge.
Which of the following plants would show curvature after the above treatment?

NTA AbhyasNTA Abhyas 2022

Solution:

Auxin is the plant hormone that is synthesized in the young stem apex. During day time, auxin redistribution occurs such that the plant side directly exposed to sunlight contains a lower auxin concentration than the other side, which is not exposed to light. This unequal distribution causes curvature. In plant-A, redistribution of auxin leads to curvature, whereas removal of the tip in plant-B leads to no auxin synthesis and no curvature. However, in plant-D, where a gelatine box with auxin is placed due to auxin redistribution, the curvature is observed.