Photosynthesis Uses Hydrogen from Water to Convert CO₂ into Glucose
In this section you need to be able to write the simple word equation for photosynthesis, where glucose is the product.
Note
HL students: To understand how carbon dioxide is converted to glucose, head to articles C1.3.11 to C1.3.19
Word Equation for Photosynthesis
The word equation for photosynthesis is as follows:
Carbon Dioxide+Water+Light Energy ⟶ Glucose+Oxygen
- Carbon Dioxide (CO₂): Absorbed from the atmosphere through the stomata in the leaves.
- Water (H₂O): Absorbed from the soil by the plant's roots.
- Light Energy: Captured by the chlorophyll in the chloroplasts and used to drive the reaction.
- Glucose (C₆H₁₂O₆): The product, which serves as the chemical energy source for the plant.
- Oxygen (O₂): Released as a byproduct into the atmosphere.
Note
- Don’t confuse the oxygen released during photosynthesis with the oxygen in carbon dioxide.
- The oxygen produced comes from water, not CO₂.
Example
For every six molecules of carbon dioxide fixed, the Calvin Cycle produces one molecule of glucose.
Why So Much Water?
- Producing one molecule of glucose requires 12 molecules of water.
- Each water molecule contributes hydrogen ions and electrons, which are essential for reducing carbon dioxide into glucose.
Note
The oxygen released during photosynthesis is a by-product of water splitting, not a direct result of glucose formation.
Self review
- Write the word equation for photosynthesis.
- What are the inputs and outputs of the process?
- Why is oxygen considered a by-product of photosynthesis?
