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.
- The C4 pathway commences with a molecule called phosphoenolpyruvate (PEP) which is a three-carbon molecule. This is the primary CO2 acceptor and the carboxylation, that takes place with the help of an enzyme called PEP carboxylase. They yield a 4-C molecule known as oxaloacetic acid (OAA).
- In due course, it is converted into another 4-carbon compound called malic acid. Later, they are shifted from mesophyll cells to bundle sheath cells. Here, OAA is crumbled to yield carbon dioxide and a 3-C molecule.
- The CO2 thus formed, is utilized in the Calvin cycle, whereas the 3-C molecule is shifted back to mesophyll cells for regeneration of PEP.
- Sugarcane, corn, and shrubs are some examples of plants that follow the C4 pathway. Calvin pathway is a very common pathway in both C3 plants and C4 plants, but it takes place only in the mesophyll cells of the C3 Plants and not in the C4 Plants.