Q1. [4]
Plants exhibit movements in response to various environmental stimuli to adopt and survive in their surroundings. These movements, influenced by external factors such as light, gravity, water and chemicals are regulated by specific plant hormones. For example, the differential growth of plant parts allows them to bend, grow or orient themselves in particular directions. Roots and shoots often show contrasting response to the same stimulus, highlighting the complex mechanisms involved in plant growth and development.
Plants exhibit movements in response to various environmental stimuli to adopt and survive in their surroundings. These movements, influenced by external factors such as light, gravity, water and chemicals are regulated by specific plant hormones. For example, the differential growth of plant parts allows them to bend, grow or orient themselves in particular directions. Roots and shoots often show contrasting response to the same stimulus, highlighting the complex mechanisms involved in plant growth and development.
- (a) Why is hydrotropism essential for plants ?
- (b) What role does auxin play in the growth of plants ?
- (c) Differentiate between movement shown by the sensitive plant and tropic movement by plants (Two points).
Previously asked in CBSE board exam
2026 31/4/1 Q15
Generated by claude-sonnet-4-6 · 2026-06-15 06:47 · grounding stimulus
Model Answer
(a) Hydrotropism is essential for plants because roots grow towards water sources, ensuring adequate water absorption for survival, photosynthesis, and other metabolic activities.
(b) Auxin is produced at the shoot tip and promotes cell elongation. It causes differential growth — cells on the shaded side elongate more, making the shoot bend towards light. In roots, even low auxin concentration inhibits growth, causing contrasting responses.
(c)
| Sensitive Plant (Mimosa) | Tropic Movement |
|---|---|
| Movement is not growth-based; it is due to loss of water from cells. | Movement is due to differential growth. |
| It is a non-directional (nastic) movement. | It is directional, in response to a specific stimulus (light, gravity, etc.). |
Source: Control and Coordination, Plant Movements and Hormones
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Explanation
- (a) is 1 mark — one crisp reason suffices.
- (b) is 1 mark — focus on auxin's role in cell elongation and bending; mention both shoot and root for completeness.
- (c) is 2 marks — examiners expect exactly two clear, contrasting points; a table format is neat and gains full marks. Key distinction: nastic (non-directional, non-growth) vs. tropic (directional, growth-based).
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