The key difference between C3, C4 and CAM pathway is the synthesis of different products during the grasping of carbon dioxide for photosynthesis from the sunlight and then conversion of it to glucose.
When photosynthetic plants yield 3-carbon acid or 3-phosphoglyceric acid(PGA) as their first product during the carbon dioxide fixation, it is known as C3 pathway. When photosynthetic plants before entering the C3 pathway produce oxaloacetic acid or 4-carbon compound as its primary product is known as Hatch and Slack or C4 pathway.
The pathway is CAM (crassulacean acid metabolism) when plants grasp the solar energy during the day and use the energy at night time to assimilate or fix carbon dioxide.
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C3 Pathway
- These temperate or cool-season plants flourish at an optimum temperature of 65-75℉, soil temperature 40-45℉
- Less efficient at higher temperatures
- Primary product is 3-phosphoglyceric acid or 3-carbon acid
- It takes place in three steps – carboxylation, reduction and regeneration
C4 Pathway
- Plants in the tropical region are observed following this pathway
- Two-step process where Oxaloacetic acid is a 4-carbon compound that is produced
- Takes place in bundle sheath and mesophyll cells found in the chloroplast
- These can either be annual or perennial and ideal temperature for their growth is 90-95℉
- Examples are Indiana grass, big bluestem, Bermudagrass,
CAM Plants
- In this type of photosynthesis, entities absorb energy during daytime from sunlight using this energy at the night aby gathering carbon dioxide
- This adaptation is observed during the time of drought, allowing gaseous exchange during the night when the temperature of the air is cooler along with loss of water vapour
- Examples are plants such as euphorbias and Cactus.
- Irregular water supply has caused bromeliads and orchids to adapt to this pathway
Difference Between C3, C4 and CAM pathway
Listed below are some significant differences
| C3 | C4 | CAM | ||
| What it means | ||||
| This pathway is observed in C3 plants wherein the primary product from sunlight post carbon-grasping is 3-phosphoglyceric acid to produce energy | Sunlight is converted into oxaloacetic acid by some plants prior to C3 cycle which is further converted into energy. The plants are known as C4 plants. It is the C4 pathway | Plants store solar energy post which they convert into energy in the night, such plants are CAM plants and the pathway is referred to as CAM pathway | ||
| Cells included | ||||
| Mesophyll cells | Bundle sheath cells, Mesophyll cells | Mesophyll cells in C3 and C4, both | ||
| Observed in | ||||
| All plants carrying out photosynthesis | Tropical plants | Semi-dry climatic conditions | ||
| Plant types that use this cycle | ||||
| Hydrophytic, Mesophytic, Xerophytic plants | Mesophytic plants | Xerophytic plants | ||
| Photorespiration process | ||||
| Observed in higher rates | Not seen as much | Observed in the noon time | ||
| First-stable product produced | ||||
| 3-phosphoglycerate | Oxaloacetate | Daytime – 3-phosphoglycerate
Night time – Oxaloacetate |
||
| Number of molecules of NADPH and ATP required to produce glucose | ||||
| NADPH – 12
ATP – 18 |
NADPH – 12
ATP – 30 |
NADPH – 12
ATP – 39 |
||
| The ideal photosynthetic temperature | ||||
| 15-25 degree celsius | 30-40 degree celsius | Greater than 40-degree celsius | ||
| Calvin cycle functional | ||||
| Not accompanied with any other cycle | Accompanied along with C4 pathway | C4 pathway and C3 | ||
| Example | ||||
| Beans, Spinach, Sunflower, Rice, Cotton | Maize, Sorghum, Sugarcane | Orchids, Cacti, euphorbias | ||
| Carboxylating enzyme | ||||
| In C3, RuBP carboxylase | PEP carboxylase – mesophyll
RuBP carboxylase – bundle sheath |
RuBP carboxylase – day time
PEP carboxylase – night time |
||
| Ratio – Co2:ATP: NADPH2 | ||||
| The ratio is 1:3:2 | The ratio is 1:5:2 | The ratio is 1:6:5:2 | ||
| Kranz Anatomy | ||||
| Not present | Present | Not present | ||
| Initial CO2 receptor | ||||
| Ribulose-1, 5-biphosphate | Phosphoenolpyruvate | Phosphoenolpyruvate | ||
| Carbon dioxide compensation point (In PPM) | ||||
| Thirty to seventy | six to ten | In dark: 0-5 | ||
These were some of the differences between the pathways. Learn more about related concepts at BYJU’S.
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