Question 9
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
(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 phosphoenol 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 photophosphorylations
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, 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 | ||
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 |
