Detailed Notes on Photosynthesis Types: C3, C4, and CAM

Photosynthesis Overview

• Definition: Photosynthesis is the process through which plants capture the energy of the sun and convert it into carbohydrates.

• Environmental Influence: The method of photosynthesis can vary among plants based on their living environment.

Types of Photosynthesis

• Overview of the three main types of photosynthesis:

  • C3 photosynthesis

  • C4 photosynthesis

  • CAM (Crassulacean Acid Metabolism) photosynthesis

C3 Photosynthesis

• Prevalence: Approximately 85% of plants engage in C3 photosynthesis.

• Name Origin: The term "C3" refers to the three-carbon molecule produced during this process.

• Location of Process:

  • Occurs primarily in mesophyll cells, which are located just beneath the leaf surface.

• Process Description:

  • CO2 uptake occurs directly and is transported to the Calvin Cycle, where it is fixed into a 3-carbon molecule.

  • If the stomata are open:

  • CO2 enters the cell.

  • Oxygen exits the cell.

  • Under hot or dry conditions, when the stomata are closed:

  • Accumulation of oxygen inhibits further production of C3 compounds due to reduced CO2 uptake.

C4 Photosynthesis

• Adaptation: C4 photosynthesis is an adaptation that enables certain plants to thrive in hot and dry conditions.

• Mechanism:

  • CO2 enters the mesophyll cell and is immediately fixed into a 4-carbon molecule.

  • The name "C4" is derived from the four-carbon molecule produced during this process.

• Anatomical Differences:

  • In C4 plants, chloroplasts are present in both mesophyll cells and bundle sheath cells (which surround the leaf veins).

• Process Flow:

  • CO2 moves from mesophyll cells to bundle sheath cells.

  • The Calvin Cycle occurs within the bundle sheath, which protects the process from oxygen buildup that can occur when stomata are closed.

CAM Photosynthesis

• Timing Adaptation: CAM photosynthesis alters the timing of CO2 uptake and fixation.

• Mechanism:

  • During the night, when the stomata are open, CO2 is absorbed and fixed into a 4-carbon molecule.

  • The 4-carbon compound is stored until daytime, providing a supply of CO2 for photosynthesis during the day when stomata are typically closed.

• Example Plant: Cacti are a prominent example of CAM plants that utilize this adaptation to thrive in arid conditions.

Summary of Key Differences

• C3 Photosynthesis:

  • CO2 is directly fixed in the Calvin Cycle.

• C4 Photosynthesis:

  • Changes the spatial location of photosynthesis, segregating the initial fixation of CO2 from the Calvin Cycle to minimize oxygen interference.

• CAM Photosynthesis:

  • Modifies the timing of photosynthesis by fixing CO2 at night and utilizing it during the day.

• Implications: These adaptations allow plants to survive in less than ideal environments, particularly those that are hot and dry, demonstrating the diversity of plant responses to environmental challenges.