Photosynthetic pathways
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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.

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Photosynthetic Pathways

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Photosynthetic pathways

Photosynthetic Pathways

  • C3 Photosynthesis:

    • Used by most plants and algae.

    • CO2 + 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 CO2 - Water conc. gradient allows some water to escape.


Photosynthetic pathways

C3 Photosynthesis


Photosynthetic pathways1

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 CO2 uptake in the C4 pathway has a higher affinity for CO2 than the enzyme used in the C3 pathway. The effect is to reduce the internal CO2 concentrations and create a steeper concentration gradient. Therefore:

      • Increases rate of CO2 diffusion inward.

      • Need fewer stomata open.

        • Conserves water


Photosynthetic pathways

C4 Photosynthesis


C4 plants usually outperform c3 plants

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

Why haven’t C4 plants taken over the world?

  • C4 photsynthesis requires more energy to fix CO2

    • 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

C4 plants are most abundant in hot dry areas

  • Percentage of C4 species in the grass flora


Photosynthetic pathways2

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.


Photosynthetic pathways

CAM Photosynthesis


Photosynthetic pathways

C3 Leaf Anatomy

C4 Leaf Anatomy


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