1. Light Absorption:
- Chlorophyll and other pigments in the chloroplasts absorb light energy from the sun.
2. Electron Transport Chain:
- The absorbed light energy splits water molecules into hydrogen ions (H+) and oxygen atoms.
- These hydrogen ions and electrons are used in the electron transport chain to generate ATP and NADPH.
- ATP (adenosine triphosphate) is an energy-rich molecule that carries chemical energy.
- NADPH (nicotinamide adenine dinucleotide phosphate) is an energy carrier that carries reducing power in the form of electrons.
3. Carbon Fixation:
- Hydrogen ions from the electron transport chain combine with carbon dioxide (CO2) from the atmosphere to form organic molecules.
- This initial fixation of carbon is catalyzed by an enzyme called ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco).
- The product of carbon fixation is an unstable molecule called 3-phosphoglycerate (3-PGA).
4. Reduction of 3-PGA:
- 3-PGA molecules are then reduced using the energy from ATP and NADPH.
- This reduction process produces molecules of glyceraldehyde-3-phosphate (G3P).
5. Glucose Formation:
- Some of the G3P molecules are used to synthesize glucose and other carbohydrates.
- The remaining G3P molecules can be used to regenerate ribulose 1,5-bisphosphate (RuBP), which is necessary for the continuation of the carbon fixation cycle.
6. Oxygen Release:
- The oxygen atoms produced during the splitting of water molecules are released into the atmosphere as a byproduct of photosynthesis.
The overall chemical equation for photosynthesis can be represented as:
6CO2 + 6H2O + light energy → C6H12O6 (glucose) + 6O2