Higher CAM Photosynthesis: The Ultimate Water-Saving Strategy

This section goes beyond the core GCSE specification but may appear in Higher tier synoptic questions.

The Problem

Desert plants face a dilemma: they need CO₂ for photosynthesis (requiring open stomata) but must minimize water loss in extreme heat.

The CAM Solution

Crassulacean Acid Metabolism (CAM) separates CO₂ uptake from photosynthesis:

Night (stomata open):

• Cool temperatures reduce transpiration
• CO₂ enters through open stomata
• CO₂ converted to malic acid and stored

Day (stomata closed):

• Stomata close to prevent water loss
• Malic acid releases CO₂ internally
• Photosynthesis proceeds using stored CO₂

Efficiency:

• CAM plants lose 50-100g water per 1g glucose made
• Normal plants lose 500-1000g water per 1g glucose
• 90% reduction in water loss