Difference Between C3, C4 and CAM pathway

The key difference between C3, C4 and CAM pathway is the synthesis of different products during the assimilation of carbon dioxide from the sunlight for photosynthesis and then conversion of it to glucose.

When photosynthetic plants yield 3-phosphoglyceric acid(PGA) or 3-carbon acid 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 their first products is known as C4 or Hatch and Slack pathway.

The pathway is CAM (crassulacean acid metabolism) when plants absorb the energy of sunlight during the day and use the energy at night time to assimilate or fix carbon dioxide.

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 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

Attributes C3 C4 CAM
What it means This pathway is observed in C3 plants wherein the first product after carbon assimilation from sunlight is 3-phosphoglyceric acid to produce energy Sunlight is converted into oxaloacetic acid by some plants before the C3 cycle which is further converted into energy. The plants are known as C4 plants and the pathway is called as C4 pathway Plants store energy from the sun and then convert it into energy during 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 both C3 and C4
Observed in All photosynthetic plants Tropical plants Semi-dry climatic conditions
Plant types that use this cycle Hydrophytic, Mesophytic, Xerophytic Mesophytic Xerophytic
Photorespiration process Observed in higher rates Not seen as much Observed in the noon time
Firs-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 temperature for photosynthesis 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 Hatch and Slack Cycle Hatch and Slack Cycle and C3
Example Beans, Spinach, Sunflower, Rice, Cotton Maize, Sorghum, Sugarcane Orchids, Cacti, euphorbias
Carboxylating enzyme RuBP carboxylase PEP carboxylase – mesophyll

RuBP carboxylase – bundle sheath

RuBP carboxylase – in the light

PEP carboxylase – in the dark

Ratio – Co2:ATP: NADPH2 1:3:2 1:5:2 1:6:5:2
Kranz Anatomy Not present Present Not present
Initial CO2 receptor Ribulose-1, 5-biphosphate Phosphoenolpyruvate Phosphoenolpyruvate
Carbon dioxide compensation point(ppm) 30-70 6-10 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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