PHOTOSYNTHESIS:
Comparison of C3, C4 and CAM plants
Topics To Cover
• Leaf anatomy
• Metabolic pathways and Catalytic enzymes
• Factors affecting photosynthetic rates
Leaf anatomy
Difference:
Present in dicot
1.
Present in monocot
1.
Cross
Section
Leaf
Anatomy
Metabolic pathways
• C3,C4 and CAM
• Carbon-fixation pathways
C3 PATHWAY
• Normal – doesn’t have photosynthetic
adaptation to reduce photorespiration
• CO2 is fixed by RUBISCO
• Produce three-carbon compound (3-PGA)
• About 85% of the plant species in the planet
• e.g., rice, wheat, soybean and all trees
C4 PATHWAY
• Light dependent and Calvin cycle is separated
• CO2 is fixed in mesophyll cells
• PEP carboxylase not RUBISCO – no tendency to
bind O2.
• Oxaloacetate – converted to Malate(same
molecule) that can be transported onto bundlesheath cells
• Thrives in hot areas
CAM PATHWAY
• Separate the process in time
instead of place.
• CO2 is fixed into oxaloacetate
by PEP carboxylase
• Organic acid or malate is stored
in vacuoles until next day
• Dominant at very hot, dry areas
Factors affecting photosynthetic rates
• Solar radiation/ Light
quantity (total of moles/sqm/s),
quality (visible light spectrum; blue and red)
– direction of the rows
angle and length of daylight
• Water
0.1% - utilized for photosynthesis
1% - to maintain hydration, turgor pressure, and biological processes
about 99% - used in transpiration
Factors affecting photosynthetic rates
• CO2 Concentration
0.034% or 340 ppm
• Mineral Elements
N, Mg – components of Chlorophyll
Fe – synthesis of Chlorophyll
P – Phosporylation process