All the plants on planet Earth can be classified on the basis of whether they use C3 or C4 pathways to synthesize carbohydrates during the dark reaction of photosynthesis process. C3 plants use Calvin cycle (discovered by Melvin Calvin) and C4 plants use Hatch–Slack pathway (discovered by Marshall Davidson Hatch and Charles Roger Slack). Both these pathways have many important differences between them. The following table lists these distinctions.
Major Differences Between C3 and C4 Plants
| Basis of Comparison | C3 Plants | C4 Plants |
|---|---|---|
| Pathway |
C3 plants use Calvin cycle. | C4 plants use Hatch–Slack pathway. |
| Abundance | 95% of all plants on Earth are C3 plants | Only 5% of all plants exhibit C4 cycle. |
| CO2 Fixation | Occurs only once | Occurs twice |
| Evolution | C3 photosynthesis in plants is much older. | C4 synthesis is a relatively new process and it evolved from C3 cycle. |
| Photorespiration | Not suppressed | Suppressed |
| Environment | Requires cool and wet environment | Requires tropical and dry environment |
| Kranz Anatomy | Leaves of C3 plants do not exhibit Kranz anatomy. | Leaves of C4 plants have Kranz anatomy. |
| Location of dark reaction | The complete dark reaction takes place in mesophyll cells. | Initial steps of the dark reaction take place in mesophyll cells and rest of the steps occur in bundle-sheath cells. |
| Chloroplast | C3 plants exhibit only granal chloroplast | C4 plants have granal as well as agranal chloroplast. |
| First Stable Product | The first stable intermediate product in dark reaction of C3 plants is a 3-carbon acid, phosphoglyceric acid. | The first stable intermediate product in dark reaction of C4 plants is a 4-carbon acid, oxaloacetate. |
| Climate | C3 Plants are common in temperate climates. | C4 plants are common in tropical climates. |
| Fixation Rate | CO2 fixation is slow | CO2 fixation is relatively faster. |
| Stomata | Photosynthesis takes place when stomata are open. | Photosynthesis takes place even when stomata are closed. |
| Examples | Examples of C3 plants are:
|
Examples of C4 plants are:
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