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Q7:
‘Both a short day plant and a long day plant can produce can flower simultaneously in a given place’. Explain.
Solution :
Theoretical Foundation: The Concept of Photoperiodism
Photoperiodism refers to the response of plants to the relative lengths of light and dark periods in a 24-hour cycle. The flowering response is determined by a critical duration of darkness, known as the critical dark period, rather than the light period itself [Per Garner and Allard’s theory of Photoperiodism].
Step 1: Definitions of Response Categories
- Short Day Plants (SDP): These plants flower when the photoperiod is shorter than a critical value. They require a long, uninterrupted dark period to trigger the transition from vegetative to reproductive growth.
- Long Day Plants (LDP): These plants flower when the photoperiod is longer than a critical value. They require a shorter dark period than their specific threshold to initiate flowering.
Step 2: Mechanism of Simultaneous Flowering
Simultaneous flowering occurs in a given location when the external environmental conditions align with the physiological requirements of both plant types. This is governed by the following factors:
- Environmental Synchronicity: If the local photoperiod is precisely at a value that satisfies the threshold for the LDP (exceeding its minimum requirement) and simultaneously satisfies the dark-period requirement for the SDP (exceeding its minimum uninterrupted dark requirement), both plants will bloom.
- Geographic Latitude & Seasonal Transition: During specific transition periods (e.g., Spring or Autumn Equinox), the day length reaches an intermediate value. At this point, the night length is long enough to satisfy the SDP’s requirement and short enough to satisfy the LDP’s requirement.
Step 3: Visual Representation of Photoperiodic Control
Step 4: Comparative Data Table
| Plant Type | Photoperiod Requirement | Critical Condition |
|---|---|---|
| Short Day Plant | Light < Critical Day Length | Uninterrupted Darkness > Critical Night Length |
| Long Day Plant | Light > Critical Day Length | Uninterrupted Darkness < Critical Night Length |
Analytical Summary
The convergence of flowering is a function of the Critical Night Length. Since the SDP requires a period of darkness longer than a specific limit and the LDP requires a period of darkness shorter than its specific limit, there exists a specific range of day lengths where both physiological "switches" are activated. This proves that photoperiodic control is species-specific and highly dependent on the intersection of individual plant sensitivity thresholds.
Final Solution: Both short-day and long-day plants can flower simultaneously if the duration of the light/dark cycle in a specific geographic location fulfills the critical night length requirements for the SDP and the critical day length requirements for the LDP concurrently, often occurring during transitional seasons.
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.
- 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.
- Q9: Would a defoliated plant respond to photoperiodic cycle? Why?
- 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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