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

By | September 27, 2021
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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 PathwayMesophyll cellsMesophyll and bundle sheath cellsMesophyll cells
Type of plantsAll photosynthetic plantsTropical plants Plants growing in desert or arid regions
DefinitionMajor type of photosynthesis – first major product formed after CO2 fixation is a three carbon compoundFirst 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
Carboxylase enzymeRuBisCOPEP carboxylase in mesophyll cells and RuBisCO in bundle sheath cells PEP carboxylase during night times and RuBisCO in day time
Intial CO2 acceptor3-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.
Leaf anatomyNormalKranzXeromorphic ( leaves show wax coating)
PhotorespirationHighMinimum 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)
Examplescereals Barley, Oats, Rice, and wheat etc..Maize, Sugarcane, sorghum etc.,orchids, cactus, pine apple, jade plant, etc.