Q1. [2] § 6.2 COORDINATION IN PLANTS § 6.2.1 Immediate Response to Stimulus
(B) Where are auxins synthesized in a plant ? Which organ of the plant shows :
(i) Positive phototropism
(ii) Negative geotropism
(iii) Positive hydrotropism
Previously asked in CBSE board exam
2023 31/4/1 Q22 (B)
Generated by claude-sonnet-4-6 · 2026-06-15 06:49 · grounding rag
Model Answer
Auxins are synthesized at the shoot tips (apical meristems) of plants.
(i) Positive phototropism — Shoot (stem); it bends towards light.
(ii) Negative geotropism — Shoot (stem); it grows away from the force of gravity.
(iii) Positive hydrotropism — Root; it grows towards water/moisture.
Explanation
- The question has two parts: synthesis site of auxins + three tropic responses. Address all parts.
- Remember: shoots show positive phototropism AND negative geotropism; roots show positive geotropism AND positive hydrotropism. This contrast is a common exam trap.
- "Positive" means growth towards the stimulus; "negative" means growth away from the stimulus.
- Auxins cause unequal cell elongation on the shaded/unstimulated side, bending the organ toward or away from the stimulus.
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