Presentation on theme: "Photosynthetic Pathways C3 Photosynthesis: Used by most plants and algae. CO 2 + ribulose bisphosphate (5 carbon sugar) = phosphoglyceric acid (3 carbon."— Presentation transcript:
Photosynthetic Pathways C3 Photosynthesis: Used by most plants and algae. CO 2 + ribulose bisphosphate (5 carbon sugar) = phosphoglyceric acid (3 carbon acid). This is called the C3 pathway because the product (phosphoglyceric acid) is a 3- carbon molecule. To fix carbon, plants must open stomata to let in CO 2 - Water conc. gradient allows some water to escape.
Photosynthetic Pathways C4 Photosynthesis Initial product of photosynthesis for this pathway is a 4-carbon molecule Acids produced during carbon fixation diffuse from mesophyll cells to bundle sheath cells. The enzyme that catalyzes CO 2 uptake in the C4 pathway has a higher affinity for CO 2 than the enzyme used in the C3 pathway. The effect is to reduce the internal CO 2 concentrations and create a steeper concentration gradient. Therefore: Increases rate of CO 2 diffusion inward. Need fewer stomata open. Conserves water
C4 plants usually outperform C3 plants C4 plants capable of higher photosynthetic rates Environments where C4 plants are more efficient: High light intensity High temperature Where water is limiting
Why haven’t C4 plants taken over the world? C4 photsynthesis requires more energy to fix CO 2 C4 spp. not well adapted to low light conditions Not found in forested or understory habitats
C4 plants are most abundant in hot dry areas Percentage of C4 species in the grass flora
Photosynthetic Pathways CAM Photosynthesis (Crassulacean Acid Metabolism) Limited to succulent plants in arid and semi- arid environments. Carbon fixation takes place at night. Reduced water loss. Low rates of photosynthesis. Extremely high rates of water use efficiency.