Comparison – C3, C4 and CAM pathways ( Photosynthesis in plants- Part VI )

Spread the love

In the previous 5 blogposts we looked into different important events taking place during the process of photosynthesis in plants.

please find the links for those blogs below –

Part I of Photosynthesis : Introduction

Part II – Light Reaction

PART III – Calvin Cycle

Part VI – Differences between Light and Dark reactions or Calvin Cycle

Part V – Photorespiration, C4 Pathway and CAM metabolism pathway

Today we will be looking into some important similarities and differences between various types of CO₂ fixation mechanisms observed in plant photosynthesis.

What are differences between C3, C4 and CAM type of Photosynthesis :

Comparison aspect	C3	C4	CAM
Cells involved in Pathway	Mesophyll cells	Mesophyll and bundle sheath cells	Mesophyll cells
Type of plants	All photosynthetic plants	Tropical plants	Plants growing in desert or arid regions
Definition	Major type of photosynthesis – first major product formed after CO₂ fixation is a three carbon compound	First major product formed after CO₂ fixation in mesophyll cells is a four carbon compound (Oxalo acetic acid ), this further breaks into a 3 carbon compound. 3 carbon compound formed enters C3 cycle in bundle sheath cells.	Fixation of CO2 occurs during night time and light absorption, glucose production involving C3 cycle occurs during day time. This process is called the CAM or crassulacean acid metabolism.
Carboxylase enzyme	RuBisCO	PEP carboxylase in mesophyll cells and RuBisCO in bundle sheath cells	PEP carboxylase during night times and RuBisCO in day time
Intial CO2 acceptor	3-Posphoglycerate (3PGA)	Oxalo acetic acid (OAA)	Oxalo acetic acid (OAA)
Dark reactions requires	12 NADPH and 18 ATPs are required.	12 NADPH and 30 ATPs are required.	12 NADPH and 39 ATPs are required.
Stomata	Open	Open	Close
Leaf anatomy	Normal	Kranz	Xeromorphic ( leaves show wax coating)
Photorespiration	High	Minimum as CO2 fixation and C3 cycle takes place in two separate cells	Minimum as CO2 fixation and C3 cycle takes place at two different times ( night and day)
Examples	cereals Barley, Oats, Rice, and wheat etc..	Maize, Sugarcane, sorghum etc.,	orchids, cactus, pine apple, jade plant, etc.