Introduction

C4 and CAM plants are two types of plants that have evolved different carbon fixation pathways to adapt to different environmental conditions. These pathways allow them to efficiently capture and utilize carbon dioxide (CO2) for photosynthesis.

C4 Plants

C4 plants are typically found in hot and dry environments, such as grasslands and tropical regions. They have a specialized anatomical and biochemical structure that helps them minimize water loss and maximize CO2 fixation.

Anatomical Structure
- C4 plants have two types of photosynthetic cells: mesophyll cells and bundle sheath cells.
- Mesophyll cells are located on the outer layer of the leaf and are responsible for initial CO2 fixation.
- Bundle sheath cells are located deeper in the leaf and surround the vascular tissue.
- These two types of cells are connected by plasmodesmata, allowing efficient transfer of metabolites.

Biochemical Pathway
- In C4 plants, initial CO2 fixation occurs in mesophyll cells through the enzyme phosphoenolpyruvate carboxylase (PEP carboxylase).
- PEP carboxylase has a higher affinity for CO2 than the enzyme Rubisco, which is responsible for CO2 fixation in most plants.
- This allows C4 plants to capture CO2 even at low concentrations.
- The product of the initial CO2 fixation, oxaloacetate, is converted into malate or aspartate and transported to the bundle sheath cells.
- In bundle sheath cells, malate or aspartate is decarboxylated, releasing CO2 for fixation by Rubisco.
- This spatial separation of initial and final CO2 fixation reduces the oxygenation of Rubisco and improves the efficiency of photosynthesis.

CAM Plants

CAM plants are typically found in arid environments, such as deserts. They have evolved a unique carbon fixation pathway called Crassulacean Acid Metabolism (CAM) to minimize water loss.

Anatomical Structure
- CAM plants have specialized cells called storage cells, which store organic acids.
- These storage cells are separate from the photosynthetic cells and are usually located in the leaves or stems.

Biochemical Pathway
- CAM plants open their stomata at night to take in CO2 when the temperature is cooler and the humidity is higher.
- CO2 is initially fixed into a 4-carbon organic acid called malate or malic acid in the storage cells using PEP carboxylase.
- During the day, when the stomata are closed to prevent water loss, malate is decarboxylated in the mesophyll cells, releasing CO2 for fixation by Rubisco.
- This temporal separation of CO2 fixation reduces water loss through transpiration.

Conclusion

C4 and CAM plants have evolved different carbon fixation pathways to adapt to different environmental conditions. C4 plants have a spatial separation of initial and final CO2 fixation, while CAM plants have a temporal separation. These adaptations allow these plants to efficiently capture and utilize CO2 while minimizing water loss, making them well-suited for hot and dry environments.