Photosynthesis works through two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle). In the light-dependent reactions, chloroplasts capture energy from sunlight to split water molecules, releasing oxygen and producing energy-rich molecules ATP and NADPH. In the Calvin cycle, ATP and NADPH are used along with carbon dioxide to synthesize glucose, a sugar molecule that plants use for energy and growth.
Basic Photosynthesis Equation
The overall chemical equation for photosynthesis is:
6CO2+6H2O+light energy→C6H12O6+6O26CO_2+6H_2O+\text{light energy}\rightarrow
C_6H_{12}O_6+6O_26CO2+6H2O+light energy→C6H12O6+6O2
This shows that six molecules of carbon dioxide and six of water, using
sunlight, produce glucose and oxygen.
Light-Dependent Reactions
- Occur in the thylakoid membranes of chloroplasts.
- Chlorophyll pigments absorb light, exciting electrons that help split water molecules.
- This releases oxygen gas as a byproduct.
- Energy from electrons is stored in ATP and NADPH molecules.
Light-Independent Reactions (Calvin Cycle)
- Use ATP and NADPH from the light reactions.
- Carbon dioxide is fixed into an organic molecule by the enzyme rubisco.
- Through a series of steps, simple sugars like glyceraldehyde 3-phosphate (G3P) are formed.
- Two G3P molecules combine to form glucose.
- The cycle regenerates molecules to continue fixing carbon dioxide.
Importance
Photosynthesis is essential for producing oxygen that most organisms breathe and for synthesizing carbohydrates that serve as food and energy for plants and consumers, including humans.
This process effectively transforms sunlight energy into chemical energy stored in glucose, sustaining life on Earth.
