(a) C3 and C4 pathways
|
C3 pathways |
C4 pathways |
|
The primary acceptor of CO2 is RUBP – a six-carbon compound. |
1. |
The primary acceptor of CO2 is phosphoenol pyruvate – a threecarbon compound. |
|
The first stable product is 3phosphoglycerate. |
2. |
The first stable product is oxaloacetic acid. |
|
It occurs only in the mesophyll cells of the leaves. |
3. |
It occurs in the mesophyll and bundle-sheath cells of the leaves. |
|
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 photophosphorylations
|
Cyclic photophosphorylation |
Non-cyclic photophosphorylation |
|
It occurs only in photosystem I. |
1. |
It occurs in photosystems I and II. |
|
It involves only the synthesis of ATP. |
2. |
It involves the synthesis of ATP
and NADPH2. |
|
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. |
|
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 |
|
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 bundlesheath 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 |
