There are three distinct biochemical variants or types of photosynthesis based on the mechanism that plants employ by which carbohydrate is formed from CO2: C3 photosynthesis, C4 photosynthesis, and CAM photosynthesis.
The table below shows their respective features.
Types of Photosynthesis
Table TP-1. Summary comparison of C3, C4, and CAM photosynthesis in plants.
| Feature | C3 Photosynthesis | C4 Photosynthesis | Cam Photosynthesis |
| Pathway of CO2 fixation | via C3 cycle only | via C3 and C4 cycles, spatially (C4 in the mesophyll cells followed by C3 in the bundle sheath cells | via C3 and C4 cycles, both spatially (in different parts of same cells) and temporally (C4 at night, C3 at daytime) |
| Normal diurnal occurrence | Daytime | Daytime | Day and night |
| Initial CO2 acceptor | Ribulose-1,5-bisphosphate (RuBP) | Phosphoenolpyruvate (PEP) | PEP at night, RuBP in the day |
| CO2-fixing enzyme | Ribulose-1,5-bisphosphate carboxylase/ oxygenase (RuBisCo) | Phosphoenolpyruvate carboxylase (PEPcase) then Rubisco | PEPcase at night, Rubisco at daytime |
| First stable product of CO2 fixation | 3-phosphoglycerate (3-PGA) | Oxaloacetate (OAA) in C4 cycle | OAA at night, 3-PGA at daytime |
| Cells Involved | Mesophyll cells | C4- mesophyll cells, C3- bundle sheath cells | Both C3 and C4 in the same mesophyll cells |
| Energy needed for complete reduction of one molecule of CO2 | 3 ATP, 2 NADPH | 5 ATP, 2 NADPH | |
| Environmental conditions favoring the most efficient photosynthesis | moderate conditions; temperature 15 °C-25°C | hot, dry conditions; temperature 30°C-47°C | extremely dry or xeric conditions; temperature ~35°C |
| Amount of water needed to produce 1 g dry matter | 450-950 g | 250-350 g | 50-55 g |
| CO2 compensation point | 30-70 ppm | 0-10 ppm | 0-5 ppm |
| Photorespiration | Yes | Absent or suppressed | Absent or suppressed |
| Annual dry matter production per hectare | ~20-25 tons | ~35-40 tons | Usually low and variable |
