Difference Between C3, C4 and Cam Pathway

Many a time you may have read in the newspaper that there is a 20 per cent reduction in yielding wheat, soybean or any other crop. But, what is that factor behind reduced yield? The answer is photorespiration. This process starts when carbon-fixing enzyme – RuBisCO encounters oxygen instead of carbon dioxide and affects the plants.


C3, C4 and Cam pathway are the adaptations that permit several plant species to lessen photorespiration in them. These pathways function in a way such that RuBisCO grabs large concentrations of carbon dioxide and prevents it from binding with oxygen. Before studying the difference between C3, C4 and Cam pathway, you must know them individually.


Notably, this is one of the vital chapters for your NEET exam and consequently, understanding their differences are of paramount importance.


C3 Pathway

In the process of photosynthesis, C3 is the most typical among the three pathways used for carbon fixation. Here, ribulose bisphosphate (RuBP), carbon dioxide and water react to form two molecules of 3-phosphoglycerate by the below-mentioned reaction.

CO2 + H2O + RuBP -> (2) 3 – phosphoglycerate

This is the first step that takes place in the Calvin-Benson cycle. Moreover, plants that completely live on C3 pathway (also called C3 plants) tend to thrive in areas with:

  • Moderate sunlight,

  • Medium temperatures,

  • Concentrations of CO2 are about 200ppm or more,

  • Ample groundwater.

Note: C3 plants have their origin from the Paleozoic and Mesozoic eras and precede C4 plants. They constitute nearly 95 per cent of plant biomass of Earth which includes essential food crops like rice, soybeans, wheat and barley.


C4 Pathway

Also known as Hatch-Slack pathway, this one is another photosynthetic process. It involves the primary step in removing carbon from CO2, to utilise it in sucrose (sugar) and various other biomolecules. The term C4 signifies the four-carbon molecule, which is the initial product of this pathway.


Plants which follow C4 carbon fixation are more advantageous than plants possessing C3 pathway under extreme conditions of temperature, drought and low carbon dioxide and nitrogen. For instance, consider C3 and C4 grasses growing in a similar environment of 30 degree Celsius. It is observed that C4 grasses lose only about 277 molecules of H2O per carbon dioxide molecule whereas C3 grasses lose 833 molecules, which is quite a high number.


There are approximately 8,100 species of plants that utilise C4 pathway, and all of them are angiosperms. Poaceae (a grass specie) uses C4 carbon fixation the most. Some crops which fall under C4 plants are:

  • Sugar cane

  • Maise

  • Millet

  • Sorghum


CAM Pathway

Crassulacean acid metabolism or CAM is the third carbon fixation procedure used by plants where the stomata remain closed during the day time to lessen evapotranspiration. But, it opens during night to gather carbon dioxide, allowing it to scatter in mesophyll cells.


Take a look at following two-part cycle that will help you in comprehending CAM pathway better.

  • During night time

As said earlier, at night CAM plants have their stomata open which allows the entry of CO2 that gets fixed like organic acids through phosphoenolpyruvate (PEP) reaction. Vacuoles store the final organic acids, which are to be used later because the Calvin cycle cannot function in the absence of NADPH and ATP.

  • During day time

To store water, stomata remains shut throughout the day time, and the organic acids which hold CO2 get released. Furthermore, an enzyme present in stroma produces carbon dioxide, which moves into Calvin cycle to enable photosynthesis.

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Plants that show CAM are mostly found in places where there are alternatively shortage and availability of water. Cacti, agave and clusia pratensis are few CAM plants examples. This type of carbon fixation is seen in aquatic plants as well. Isoetes, Littorella, Crassula and Sagittaria are four genera of marine species which follows CAM photosynthesis.


Now that you have been enlightened with C3 C4 and CAM carbon fixation separately let us move on with the difference between C3, C4 and CAM pathway.


A tabular depiction of C3, C4 and CAM plants.


Difference Between C3, C4 and CAM Pathway


Basis of Differentiation

C3

C4

CAM

Including cells

Mesophyll cells.

Bundle sheath and mesophyll cells.

Mesophyll cells in C3 and C4 both.

Found in

All plants following photosynthesis.

Tropical plants.

Plants growing in semi-arid conditions.

Plants following this type of cycle

Xerophytic, Mesophytic and Hydrophytic.

Mesophytic

Xerophytic

Photorespiration procedure

Seen at larger rates.

Not seen much.

Seen in noon time.

First released product

3-phosphoglycerate

Oxaloacetate

3-phosphoglycerate in day time and oxaloacetate in night.

Number of NADPH and ATP molecules needed to release glucose

NADPH- 12

ATP- 18

NADPH- 12

ATP- 30

NADPH- 12

ATP- 39

Suitable temperature for photosynthesis

15 – 25 degrees

30 – 40 degrees

More than 40 degrees.

Carboxylating enzyme

RuBP carboxylase

RuBP carboxylase- bundle sheath,

PEP carboxylase- mesophyll.

PEP carboxylase- in light,

RuBP carboxylase- in dark.

Cycle accompanied with Calvin

No other cycle accompanied.

Hatch and Slack Cycle.

C3 and Hatch and Slack Cycle.

Examples

Rice, sunflower, cotton.

Sugarcane, maize, sorghum.

Cacti, orchids, agave.


Prepare Thoroughly for NEET 

Biology curriculum of NEET is vast, and you must study every single chapter by heart. Failing which, you will not secure your desired score.


Furthermore, it is essential to put more emphasis on vital topics like difference between C3, C4 and CAM plants, as there are chances of questions getting repeated from this portion. Besides studying, take good care of your health and provide yourself with short breaks as it is equally important to stay fit before your examination.

All the best!

FAQ (Frequently Asked Questions)

1. Why are C3 Plants Unable to Grow in Scorching Places?

Ans. As temperature rises, RuBisCO assimilates more O2 into RuBP. As a result, photorespiration occurs, which promotes complete loss of nitrogen and carbon from the plant and consequently can restrict growth.

2. Which Characteristic Leaf Anatomy do C4 Plants Possess?

Ans. The C4 plants hold Kranz leaf anatomy.

3. How Many Species Follow the CAM Process?

Ans. CAM pathway occurs approximately in 16,000 species which is about 7 percent of Earth’s plants.

4. What are CAM Plants?

Ans. CAM plants refer to those plants who can survive in arid conditions where loss of water is a prime factor that limits plant growth.