Types of Photosynthesis: Summary Comparison of C3, C4, and Cam

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.

FeatureC3 PhotosynthesisC4 PhotosynthesisCam Photosynthesis
Pathway of
CO2 fixation
via C3 cycle onlyvia 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
DaytimeDaytimeDay 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 RubiscoPEPcase 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 cellsC4- 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 NADPH5 ATP, 2 NADPH
Environmental conditions favoring the most efficient photosynthesis
moderate conditions; temperature
15 °C-25°C
hot, dry conditions; temperature 30°C-47°Cextremely dry or xeric conditions; temperature ~35°C
Amount of
water needed
to produce 1 g dry matter
450-950 g250-350 g50-55 g
CO2 compensation point30-70 ppm0-10 ppm0-5 ppm
PhotorespirationYesAbsent or
suppressed
Absent or
suppressed
Annual dry matter production per hectare
~20-25 tons~35-40 tonsUsually low and variable
Sources: Mathews and Van Holde (1990); Hopkins (1999); Moore et al. (2003); Simpson (2010)

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