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Q9(c):
Give comparison between the following:
(c) Anatomy of leaf in $C_3$ and $C_4$ plants
Solution :
Step 1: Structural Basis of $C_3$ and $C_4$ Anatomy
The fundamental distinction in leaf anatomy between $C_3$ and $C_4$ plants lies in the spatial organization of photosynthetic tissues. While $C_3$ plants utilize a standard mesophyll arrangement, $C_4$ plants have evolved a specialized morphology known as Kranz Anatomy [Per the Evolutionary Adaptations for Photorespiration Suppression].
Step 2: Comparative Anatomical Analysis
| Characteristic | $C_3$ Leaf Anatomy | $C_4$ Leaf Anatomy |
|---|---|---|
| Mesophyll Differentiation | Differentiated into palisade and spongy parenchyma. | Undifferentiated; cells are radially arranged around the bundle sheath. |
| Bundle Sheath Cells | Small, thin-walled, and lack chloroplasts or contain few. | Large, thick-walled, and contain numerous prominent chloroplasts. |
| Kranz Anatomy | Absent. | Present (Wreath-like arrangement of mesophyll). |
| Chloroplast Dimorphism | Absent (All chloroplasts are structurally similar). | Present (Mesophyll chloroplasts are granal; Bundle sheath chloroplasts are agranal). |
Step 3: Visual Representation of Leaf Anatomy
Step 4: Functional Justification
In $C_4$ anatomy, the Kranz anatomy serves to spatially separate the initial $CO_2$ fixation and the Calvin cycle. The radial arrangement of mesophyll cells allows for high-efficiency capture of $CO_2$ by Phosphoenolpyruvate (PEP) carboxylase [Per the C4 Cycle mechanism]. The large, thick-walled bundle sheath cells, containing agranal chloroplasts, maintain high internal $CO_2$ concentrations, which effectively inhibits the oxygenase activity of RuBisCO, thereby suppressing photorespiration [Justified by the lack of direct $O_2$ access in the sheath]. Conversely, in $C_3$ plants, mesophyll cells perform all light-dependent and dark reactions in a single cell type, rendering them susceptible to photorespiratory losses when temperatures rise.
Final Solution: The fundamental anatomical difference is the presence of Kranz anatomy in $C_4$ plants (radially arranged mesophyll around large, chloroplast-rich bundle sheath cells), which is absent in $C_3$ plants, facilitating specialized spatial separation of the photosynthetic pathway.
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?
- 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
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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