How does photosynthesis work?
Short answer
Photosynthesis is the process plants use to make glucose. In the chloroplasts, chlorophyll absorbs light energy, which is used to convert carbon dioxide and water into glucose and oxygen. The word equation is: carbon dioxide + water gives glucose + oxygen, using light energy.
Step by step
- Water is absorbed from the soil by the roots and travels up the xylem to the leaves.
- Carbon dioxide diffuses into the leaf through small pores called stomata.
- Chlorophyll in the chloroplasts absorbs light energy.
- The energy is used to make glucose. Oxygen is released as a by-product through the stomata.
- Glucose is used for respiration, or stored as starch, or used to make cellulose and proteins.
Worked example
Balanced symbol equation
- 6CO₂ + 6H₂O gives C₆H₁₂O₆ + 6O₂
- Light energy is needed, and chlorophyll absorbs it
- Photosynthesis is endothermic: it takes in energy
Common mistakes
- Saying plants get their food from the soil. They make it; the soil supplies water and minerals.
- Saying plants photosynthesise instead of respiring. Plants respire all the time, day and night.
- Forgetting the limiting factors: light intensity, carbon dioxide concentration and temperature.
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