Question:
Give comparison between the following: - C3 and C4 pathways
- Cyclic and non-cyclic photophosphorylation
- Anatomy of leaf in C3 and C4 plants
Give comparison between the following:
- C3 and C4 pathways
- Cyclic and non-cyclic photophosphorylation
- Anatomy of leaf in C3 and C4 plants
Updated On: Nov 20, 2023
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Solution and Explanation
a. C3 and C4 pathways
| C3 pathways | C4 pathways | ||
|---|---|---|---|
| 1 | The primary acceptor of CO2 is RUBP – a six-carbon compound. | 1 | The primary acceptor of CO2 is phosphonyl pyruvate – a three-carbon compound. |
| 2 | The first stable product is 3-phosphoglycerate. | 2 | The first stable product is oxaloacetic acid. |
| 3 | It occurs only in the mesophyll cells of the leaves. | 3 | It occurs in the mesophyll and bundle-sheath cells of the leaves. |
| 4 | It is a slower process of carbon fixation and photo-respiratory losses are high. | 4 | It is a faster process of carbon fixation and photo-respiratory losses are low. |
b. Cyclic and non-cyclic photophosphorylation
| Cyclic photophosphorylation | Non-cyclic photophosphorylation | ||
|---|---|---|---|
| 1 | It occurs only in photosystem I. | 1 | It occurs in photosystems I and II. |
| 2 | It involves only the synthesis of ATP | 2 | It involves the synthesis of ATP and NADPH2. |
| 3 | In this process, electrons move in a closed circle. | 3 | In this process, electrons move in a closed circle. |
c. Anatomy of leaf in C3 and C4 plants
| C3 leaves | C4 leaves | ||
|---|---|---|---|
| 1 | Photorespiration occurs | 1 | Photorespiration does not occur. |
| 2 | RuBisCo is present in the mesophyll cells. | 2 | RuBisCo is present in the bundle-sheath cells. |
| 3 | The first stable compound produced is 3-phosphoglycerate –a three-carbon compound. | 3 | The first stable compound produced is oxaloacetic acid – a four-carbon compound. |
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Concepts Used:
C4 Pathway
- Every photosynthetic plant moves according to the Calvin cycle, but in some plants, there is a primary stage to the Calvin Cycle called the C4 pathway. Plants in tropical desert regions commonly move accordingly to the C4 pathway. Here, a 4-carbon compound called oxaloacetic acid (OAA) is the first product of carbon fixation. Such plants are special and have specific adaptations as well.
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