Question

Give comparison between the following:

1. C3 and C4 pathways
2. Cyclic and non-cyclic photophosphorylation
3. Anatomy of leaf in C3 and C4 plants

Answer 1

a. C3 and C4 pathways

| C 3 pathways| | C 4 pathways
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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.

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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.

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c. Anatomy of leaf in C3 and C4 plants

| C 3 leaves| | C 4 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.