Photosynthesis: Capturing Energy from Light
Organisms are divided into autotrophs (producers that make their own food) and heterotrophs (consumers that get energy by eating other organisms). Photosynthesis is an endergonic process requiring energy input, transforming light energy into chemical energy stored in glucose.
Photosynthesis takes place in chloroplasts containing the green pigment chlorophyll, which absorbs light energy. These chloroplasts are found in the mesophyll tissue of leaves, with stomata (pores) allowing CO₂ to enter and O₂ to exit during the process.
The process has two main stages. Light reactions occur in the thylakoid membrane where light energy is captured by photosystems I and II. Water is split, releasing oxygen, and energy is transferred through electron transport chains to produce ATP and NADPH. The Calvin cycle uses these energy carriers in the stroma to incorporate CO₂ into sugar molecules called G3P, requiring 9 ATP and 6 NADPH for each complete cycle.
Try This! Draw a simple diagram connecting the light reactions to the Calvin cycle, showing how ATP and NADPH move between them. This visual connection will help you understand how these processes work together.
