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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?
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?
Solution :
Theoretical Framework of Light Intensity and Photosynthesis
The relationship between light intensity and the rate of photosynthesis is characterized by a non-linear trajectory. Initially, as light intensity increases, the rate of photosynthesis increases linearly because light energy is the limiting factor [Per the Law of Limiting Factors by Blackman, 1905]. As intensity continues to rise, the rate becomes limited by other environmental factors (e.g., $CO_2$ concentration or temperature), resulting in a plateau.
Step 1: Identifying Point C (The Transition Phase)
Point C represents the stage where the rate of photosynthesis begins to deviate from a linear progression. At this intensity, light is no longer the sole limiting factor. Internal cellular processes or the concentration of $CO_2$ start to influence the rate of carbon fixation [Justification: Principles of Physiological Ecology]. The curve at Point C is in a state of diminishing returns.
Step 2: Identifying Point D (The Light Saturation Point)
Point D corresponds to the Light Saturation Point. At this specific intensity, the rate of photosynthesis reaches a maximum plateau ($P_{max}$). Beyond this value, increasing the light intensity further yields no significant increase in the rate of photosynthesis because the light-independent reactions (Calvin Cycle) or the availability of enzymes (e.g., RuBisCO) and substrates become the absolute limiting factors [Per the Law of Limiting Factors].
Analytical Comparison Table
| Feature | Point C | Point D |
|---|---|---|
| Definition | Transition phase | Saturation point |
| Limiting Factor | Light is co-limiting | Other factors (CO2/Temperature) |
| Rate Status | Increasing at a decreasing rate | Maximum constant rate |
Final Solution: Point C represents the stage of transition where light intensity starts to become saturated and other factors begin to limit the rate; Point D represents the light saturation point where the rate of photosynthesis reaches its maximum and remains constant despite further increases in light intensity.
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(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?
- 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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