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Q7:
Look at leaves of the same plant on the shady side and compare it with the leaves on the sunny side. Or, compare the potted plants kept in the sunlight with those in the shade. Which of them has leaves that are darker green ? Why?
Solution :
1. Empirical Observation and Comparative Analysis
When comparing leaves from a sunny environment versus a shady environment, empirical observation reveals that leaves grown in the shade exhibit a darker green coloration compared to those exposed to direct, high-intensity sunlight. This phenomenon is a physiological adaptation driven by the necessity to maximize photosynthetic efficiency under light-limiting conditions.
2. Physiological Mechanisms and Chlorophyll Density
The intensity of green coloration in a leaf is directly proportional to the density of chlorophyll pigments within the mesophyll cells [Per the Beer-Lambert Law application in biological systems].
- Shade-Adapted Leaves (Sciophytes): In low-light conditions, the plant prioritizes the capture of scarce photons. To compensate for reduced light availability, these leaves increase the concentration of chlorophyll per unit area of the leaf. This results in a thicker density of light-harvesting complexes (LHCs) within the thylakoid membranes [By the principles of Photo-acclimation].
- Sun-Adapted Leaves (Heliophytes): In high-intensity light, the photon flux is often saturating. Excessive chlorophyll density could lead to photo-oxidation or photo-inhibition. Therefore, these leaves typically exhibit a higher ratio of carotenoids (which provide photoprotection) and have a larger surface area to dissipate heat, leading to a lighter, sometimes yellowish-green, appearance.
3. Comparative Data Summary
| Characteristic | Sun-Grown Leaf | Shade-Grown Leaf |
|---|---|---|
| Chlorophyll Content | Lower | Higher |
| Leaf Color | Light Green | Dark Green |
| Photosynthetic Adaptation | High light saturation capacity | High light-harvesting efficiency |
4. Structural Visualization of Chlorophyll Distribution
5. Conclusion of Analysis
The darker green color in shade leaves is a morphological and biochemical response known as shade-induced greening. By increasing the chlorophyll content, the plant optimizes its ability to harvest the limited quanta of light available in shaded environments, ensuring that the light-dependent reactions of photosynthesis can proceed at a rate sufficient to maintain metabolic homeostasis [Justified by the Law of Limiting Factors, Blackman, 1905].
Final Solution: Leaves grown in the shade are darker green because they possess a higher density of chlorophyll pigments, which allows the plant to maximize photon capture in light-deficient environments.
More Questions from Class 11 Biology Photosynthesis EXERCISES
- Q1: By looking at a plant externally, can you tell whether a plant is $C_3$ or $C_4$? Why and how?
- Q2: By looking at which internal structure of a plant you can tell whether a plant is $C_3$ or $C_4$? Explain.
- Q3: Even though a very few cells in a $C_4$ plant carry out the biosynthetic – Calvin pathway, yet they are highly productive. Can you discuss why?
- Q4: RuBisCO is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCO carries out more carboxylation in $C_4$ plants?
- Q5: Suppose there were plants that had a high concentration of Chlorophyll $b$, but lacked chlorophyll $a$, would it carry out photosynthesis? Then why do plants have chlorophyll $b$ and other accessory pigments?
- Q6: Why is the colour of a leaf kept in the dark frequently becomes yellow, or pale green? Which pigment do you think is more stable?
- Q8(a): Figure 11.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions: (a) At which point/s (A, B or C) in the curve light is a limiting factor?
- Q8(b): Figure 11.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions: (b) What could be the limiting factor/s in region A?
- Q8(c): Figure 11.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions: (c) What do C and D represent on the curve?
- Q9(a): Give comparison between the following: (a) $C_3$ and $C_4$ pathways
- Q9(b): Give comparison between the following: (b) Cyclic and non-cyclic photophosphorylation
- Q9(c): Give comparison between the following: (c) Anatomy of leaf in $C_3$ and $C_4$ plants
CBSE Solutions for Class 11 Biology Photosynthesis
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
- Respiration in Plants
- Plant Growth and Development
- 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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