Question:
Give comparison between the following: (a) C3 and C4 pathways (b) Cyclic and non-cyclic photophosphorylation (c) Anatomy of leaf in C3 and C4 plants
Answer:
(a) C3 and C4 pathways
|
C3 pathways |
C4 pathways |
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|
1. |
The primary acceptor of CO2 is RUBP which is a six-carbon compound. |
1. |
The primary acceptor of CO2 is phosphoenol pyruvate which is 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.
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(b) Cyclic and non-cyclic photophosphorylations
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Cyclic photophosphorylation |
Non-cyclic photophosphorylation |
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|
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, photolysis of water does not occur. Therefore, oxygen is not produced. |
3. |
In this process, photolysis of water takes place and oxygen is liberated. |
|
4. |
In this process, electrons move in a closed circle. |
4. |
In this process, electrons do not move in a closed circle. |
(c) Anatomy of the leaves in C3 and C4 plants
|
C3 leaves |
C4 leaves |
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|
1. |
Bundle-sheath cells are absent |
1. |
Bundle-sheath cells are present |
|
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. |
|
4. |
Photorespiration occurs |
4. |
Photorespiration does not occur |
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