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Q9:
Would a defoliated plant respond to photoperiodic cycle? Why?
Solution :
Theoretical Foundation: The Site of Photoperiodic Perception
Photoperiodism refers to the physiological response of organisms to the length of day or night. In angiosperms, this process is governed by the perception of light stimuli and the subsequent signaling pathways that trigger floral transition. The primary site of perception for photoperiodic stimuli is the leaves [Per the florigen hypothesis and light-reception studies].
Step 1: The Mechanism of Stimulus Perception
Leaves contain specialized photoreceptor proteins, primarily phytochromes and cryptochromes, which absorb light of specific wavelengths (Red/Far-red and Blue light). Upon exposure to the appropriate photoperiod (the critical day length), the leaves synthesize a mobile signaling molecule known as florigen [Reference: Chailakhyan’s Florigen Hypothesis].
Step 2: The Role of Mobile Signaling (Florigen)
Once synthesized in the leaf lamina, this signaling molecule—identified in modern molecular biology as the protein product of the FLOWERING LOCUS T (FT) gene—is translocated via the phloem to the shoot apical meristem. Only upon reaching the meristem does this signal induce the biochemical reprogramming necessary to transition the vegetative buds into floral buds.
Step 3: Evaluation of the Defoliated State
If a plant is defoliated, the primary sites of light perception and signal synthesis are removed. Without the presence of leaves to perceive the critical dark/light periods and synthesize the inductive signal, the shoot apical meristem remains in a vegetative state, irrespective of the environmental light cycles. The plant loses its capability to translate environmental duration into developmental signals.
Analytical Conclusion
| Component | Function in Photoperiodism |
|---|---|
| Leaves | Perception of photoperiod and synthesis of florigen. |
| Phloem | Translocation of florigen to the apex. |
| Shoot Apex | Target tissue that differentiates into flowers. |
By removing the leaves, the communication loop between the environment and the meristem is severed. Thus, the plant cannot perceive the stimulus required to initiate the reproductive phase.
Final Solution: No, a defoliated plant would not respond to a photoperiodic cycle because the leaves are the site of perception for photoperiodic stimuli and the synthesis of the mobile flowering hormone (florigen), which is required to initiate flowering at the shoot apical meristem.
More Questions from Class 11 Biology Plant Growth and Development EXERCISES
- Q1: Define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate.
- Q2: Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?
- Q3(a): Describe briefly: (a) Arithmetic growth
- Q3(b): Describe briefly: (b) Geometric growth
- Q3(c): Describe briefly: (c) Sigmoid growth curve
- Q3(d): Describe briefly: (d) Absolute and relative growth rates
- Q4: List five main groups of natural plant growth regulators. Write a note on discovery, physiological functions and agricultural/horticultural applications of any one of them.
- Q5: Why is abscisic acid also known as stress hormone?
- Q6: ‘Both growth and differentiation in higher plants are open’. Comment.
- Q7: ‘Both a short day plant and a long day plant can produce can flower simultaneously in a given place’. Explain.
- Q8(a): Which one of the plant growth regulators would you use if you are asked to: (a) induce rooting in a twig
- Q8(b): Which one of the plant growth regulators would you use if you are asked to: (b) quickly ripen a fruit
- Q8(c): Which one of the plant growth regulators would you use if you are asked to: (c) delay leaf senescence
- Q8(d): Which one of the plant growth regulators would you use if you are asked to: (d) induce growth in axillary buds
- Q8(e): Which one of the plant growth regulators would you use if you are asked to: (e) ‘bolt’ a rosette plant
- Q8(f): Which one of the plant growth regulators would you use if you are asked to: (f) induce immediate stomatal closure in leaves.
- Q10(a): What would be expected to happen if: (a) $GA_3$ is applied to rice seedlings
- Q10(b): What would be expected to happen if: (b) dividing cells stop differentiating
- Q10(c): What would be expected to happen if: (c) a rotten fruit gets mixed with unripe fruits
- Q10(d): What would be expected to happen if: (d) you forget to add cytokinin to the culture medium.
CBSE Solutions for Class 11 Biology Plant Growth and Development
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Cell Cycle and Division
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Digestion and Absorption
- Breathing and Exchange of Gases
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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