PREVIOUSLY ASKED IN:
WBPSC Miscellaneous Preliminary 2019
Answer
water
Explanation
During the process of photosynthesis, the oxygen gas that is liberated into the atmosphere comes entirely from the splitting of water (H2O) molecules. This light-dependent process is known as the photolysis of water. The energy from sunlight is used to break water into hydrogen ions, electrons, and oxygen gas. This specific mechanism was demonstrated by Robert Hill, hence it is also called the Hill reaction. The carbon and oxygen from Carbon Dioxide (CO2) are used to synthesize the primary product, glucose.
Key Points
- > The photolysis of water takes place during the light-dependent reactions of photosynthesis.
- > The light reactions occur in the thylakoid membranes (grana) of the chloroplast.
- > The main product of photosynthesis is the simple carbohydrate glucose (C6H12O6).
- > The dark reaction (Calvin cycle), where CO2 is reduced to form glucose, occurs in the stroma of the chloroplast.
- > Photosynthesis essentially converts solar energy into chemical energy stored in organic bonds.
Additional Information
Elements of Photosynthesis & Their Roles
| Element | Source | Primary Role |
|---|---|---|
| Carbon Dioxide (CO2) | Atmosphere (via stomata) | Carbon source for producing Glucose |
| Water (H2O) | Soil (via roots) | Electron donor and source of Oxygen gas |
| Sunlight | Sun | Provides energy for the reaction |
| Chlorophyll | Green leaves | Captures light energy (photons) |
Memory Tips
- Oxygen Source Trick: Think of the word WATER washing away to leave OXYGEN in the air. The O from CO2 goes into the solid sugar (glucose).