- Discuss the main events that occur in the Calvin-Bensen cycle, and tell the cycle must turn six times in order to generate a 6-carbon sugar.
- Explain the process of photo respiration, and describe the environmental conditions that favor this process.
- Discuss the C4 and CAM pathways; explain why C4 plants photosynthesize more efficiently than C3 plants.
- Describe the global carbon cycle.
Light Independent ReactionsThe light independent reactions are also known as the dark reactions or Calvin Cycle and utilize the ATP and NADPH from the light-dependent reactions to fix gaseous CO2 into carbohydrate backbones. Photosynthesis is often simplified into 6CO2 + 6H2O + light –> C6H12O6 + 6O2 . However, the true product is 3-phosphoglycerate that can be used to generate longer carbohydrates like glucose. The starting point of carbon fixation is the carbohydrate Ribulose 1,5-bisphosphate. The enzyme Ribulose Bisphospate Carboxylase (RuBisCO) captures a CO2 molecule onto Ribulose 1,5-bisphosphate to generate 2 molecules of 3-phosphoglycerate which can enter the process of gluconeogenesis to generate glucose. ATP from the light reactions can then facilitate the conversion of 3-phosphoglycerate to 1,3 bisphosphoglycerate which can be reduced by NADPH to glyceraldehyde-3-phosphate (G3P). G3P can then be used to regenerate Ribulose 1,5-bisphosphate.
Crassulacean acid metabolism (CAM)
CAM (Crassulacean acid metabolism) photosynthesis is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. At night, stomata open to permit the entry of CO2 into cells for storage as organic acids in vacuoles. During the day, the stomata close to conserve water and the stored CO2 enters the stroma of chloroplasts to take part int eh Calvin Cycle reactions.