C4 Plants

Edexcel A-level BiologyPhotosynthesisLesson 14 of 20

In most plants, called C3 plants, the first product of carbon fixation is GP, a 3-carbon compound. RUBISCO has a drawback: at high temperatures and low CO₂ concentrations it increasingly combines with oxygen instead of CO₂. This process, photorespiration, wastes energy and releases fixed carbon. It is a serious problem in hot, bright conditions, where stomata close to save water and the CO₂ concentration in the leaf falls.

C4 plants, such as maize and sugar cane, avoid this by fixing CO₂ twice, in two different cell types (Kranz anatomy).

More in Photosynthesis

• Non-Cyclic Photophosphorylation
• The Light-Independent Stage
• The Calvin Cycle
• The Products of Photosynthesis
• Rubisco
• Limiting Factors of Photosynthesis
• Light
• Carbon Dioxide

All 20 lessons in Photosynthesis · All Edexcel A-level Biology topics