Lecture Notes: Crassulation Acid Metabolism (CAM) Photosynthesis

Introduction

• Presenter: Andrew Douch
• Topic: CAM Photosynthesis
• Misleading Terminology: "Crassulation Acid Metabolism" (CAM)
  • No actual "crassulation acid"
  • Name derives from plant family "Crassulaceae"

CAM Photosynthesis

• Found in plants adapted to dry environments
  • Examples:
    • Crassulaceae (e.g., stone crops)
    • Cactaceae (cacti)
    • Bromeliaceae (includes pineapples)
    • Some epiphytic orchids (live on tree branches)

Importance and Function

• Helps plants manage water loss in arid conditions
• Allows photosynthesis to occur with minimized water loss

Photosynthesis Process Overview

1. Two Stages:
   • Light-Dependent Stage (occurs in thylakoid membranes)
   • Light-Independent Stage (Calvin Cycle, occurs in the stroma of chloroplasts)
2. Key Enzyme:
   • Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase)

The Problem

• Stomata Function:
  • Open and close to allow gas exchange
  • Problem: Open stomata lead to water loss, which is problematic in dry environments

CAM Photosynthesis: Solution

• Nighttime Process:
  • Stomata open to take in carbon dioxide
  • Cooler temperatures reduce water loss
  • Carbon dioxide combines with PEP (phosphoenolpyruvate) to form malic acid
• Daytime Process:
  • Stomata close to minimize water loss
  • Stored malic acid is converted back to carbon dioxide and enters Calvin Cycle
  • Enables photosynthesis to proceed with closed stomata

Key Molecules Involved

• PEP (Phosphoenolpyruvate):
  • Combines with carbon dioxide at night
• Malic Acid:
  • Stores carbon dioxide in vacuole
• Calvin Cycle:
  • Uses stored carbon dioxide for photosynthesis

Conclusion

• CAM photosynthesis is an adaptation for water conservation
• Allows plants to photosynthesize efficiently in arid conditions

Summary

• CAM enables plants to save carbon dioxide at night and use it during the day without losing water from open stomata.
• Effective adaptation for survival in water-scarce environments.