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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?
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?
Solution :
Analysis of Region A: Limiting Factors in Photosynthesis
In the standard representation of the light-response curve of photosynthesis, the graph plots the Rate of Photosynthesis (y-axis) against Light Intensity (x-axis). Region A represents the initial, linear portion of the curve where the photosynthetic rate increases proportionally with light intensity.
Step 1: Application of Blackman’s Law of Limiting Factors
Per Blackman’s Law of Limiting Factors (1905), if a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value; it is the factor which directly affects the process if its quantity is changed.
Step 2: Identification of Constraints in Region A
In Region A, the rate of photosynthesis is strictly dependent on the light intensity. As light intensity increases, the rate of production of $ATP$ and $NADPH$ (the products of the light-dependent reactions) increases proportionally. Consequently, the rate of $CO_2$ fixation is directly limited by the availability of these light-generated products [Per the Light-Dependent Reaction stoichiometry].
- Primary Limiting Factor: Light Intensity. Because the curve is linear and rising, the enzymatic machinery ($RuBisCO$) and $CO_2$ concentrations are in excess relative to the photon flux density.
- Secondary Potential Limiting Factors: While light is the dominant limiting factor, if conditions were altered, factors such as $CO_2$ concentration or ambient temperature could also become limiting if they are held at non-saturating levels. However, in the context of standard light-response dynamics, Light Intensity is the governing parameter for Region A.
Visual Representation of Light Saturation Dynamics
Summary Analysis
The linearity of the graph in Region A indicates that the system has not yet reached light saturation. Therefore, any increment in light intensity results in a proportional increment in the photosynthetic rate. If the rate were limited by other factors (such as $CO_2$ or enzymes), the curve would deviate from this linear trajectory before the light saturation point is reached.
Final Solution: The limiting factor in region A is Light Intensity. As the light intensity increases, the rate of photosynthesis increases linearly, confirming that light is the factor nearest to its minimum value per Blackman's Law of Limiting Factors.
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?
- 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?
- 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(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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