Overview of Photosynthesis Pathways
Photosynthesis in plants converts light energy into chemical energy through two main biochemical pathways: the light-dependent reactions and the light-independent reactions (Calvin cycle). These occur in chloroplasts, where chlorophyll absorbs sunlight to drive electron transport and carbon fixation, producing glucose and oxygen as byproducts.
Light-Dependent Reactions
In the thylakoid membranes, light excites electrons in photosystems II and I, leading to photolysis of water, which releases oxygen and protons. This creates ATP via photophosphorylation and NADPH through electron transport, providing energy carriers for the subsequent Calvin cycle. Key enzymes include ATP synthase and ferredoxin-NADP+ reductase.
Light-Independent Reactions (Calvin Cycle)
In the stroma, the Calvin cycle fixes CO2 into organic molecules using ATP and NADPH from light reactions. Rubisco catalyzes the carboxylation of ribulose-1,5-bisphosphate (RuBP) to form 3-phosphoglycerate, which is reduced to glyceraldehyde-3-phosphate (G3P). Some G3P forms glucose, while the rest regenerates RuBP in a cyclic process.
Applications and Importance in Plant Biology
These pathways are essential for plant growth, enabling carbon assimilation and oxygen production, which sustains global ecosystems. Understanding them aids in improving crop yields through genetic engineering of enzymes like Rubisco, addressing food security and climate change by enhancing photosynthetic efficiency.