Understanding C3, C4, and CAM Pathways in Plants

C3, C4, and CAM Pathways in Plants

Plants have evolved unique photosynthetic pathways to adapt to their environments. The three main pathways are C3, C4, and CAM.

C3 Pathway

• Occurs in all photosynthetic plants
• Fixes CO2 into 3-phosphoglyceric acid (3-PGA) via the Calvin cycle
• Takes place in mesophyll cells
• Less efficient at high temperatures and low CO2 levels
• Examples: Sunflower, spinach, beans, rice, cotton

C4 Pathway

• Found in tropical plants like sugarcane, maize, and sorghum
• Fixes CO2 into oxaloacetic acid (OAA), a 4-carbon compound
• Occurs in mesophyll and bundle sheath cells
• More efficient than C3 pathway, especially in hot and dry environments
• Reduces photorespiration and increases water use efficiency

CAM Pathway

• Occurs in succulent plants like cacti and orchids
• Fixes CO2 at night into malic acid, which is stored in vacuoles
• During the day, malic acid is decarboxylated, releasing CO2 for photosynthesis
• Helps conserve water by keeping stomata closed during the day
• Adapted to arid environments with limited water availability

Key Differences

• Optimum Temperature: C3 (15-25°C), C4 (30-40°C), CAM (>40°C)
• Water Use Efficiency: CAM > C4 > C3
• Photorespiration: C3 plants experience more photorespiration than C4 and CAM plants
• Cell Types: C3 (mesophyll cells), C4 (mesophyll and bundle sheath cells), CAM (mesophyll cells with both C3 and C4 processes)

These pathways enable plants to thrive in diverse environments, from tropical to arid regions