The Photosynthesis Equation

Word equation:

carbon dioxide + water →light energy→ glucose + oxygen

Balanced symbol equation:

6CO₂ + 6H₂O →light energy→ C₆H₁₂O₆ + 6O₂

Key features:

  • Raw materials (reactants): CO₂ (from the air, enters through stomata) and H₂O (from the soil, absorbed by roots and transported via xylem).
  • Energy source: Light energy absorbed by chlorophyll in chloroplasts.
  • Products: Glucose (C₆H₁₂O₆): used for energy and as a building block. Oxygen (O₂): released as a by-product through stomata.
  • Site: Chloroplasts in the mesophyll cells of leaves.

What Happens to the Glucose?

Plants use the glucose produced by photosynthesis in several ways:

  • Respiration: glucose is broken down to release energy for cell processes. This occurs in ALL plant cells, day and night.
  • Converted to starch: for storage. Starch is insoluble, so it does not affect osmosis. Stored in leaves, seeds and storage organs (e.g. Potato tubers).
  • Converted to cellulose: for making cell walls.
  • Converted to lipids (fats and oils): for energy storage in seeds.
  • Converted to amino acids: combined with nitrate ions absorbed from the soil to make amino acids, then proteins for growth.
  • Converted to sucrose: for transport in the phloem to other parts of the plant.

Why Photosynthesis Matters

Photosynthesis is fundamental to life on Earth:

  • It is the source of food for almost all organisms: plants are producers at the base of food chains.
  • It produces oxygen: essential for aerobic respiration in most organisms.
  • It removes CO₂ from the atmosphere: helping to regulate atmospheric composition.
  • It stores energy from the sun in chemical form: this energy flows through ecosystems via food chains.

Energy conversion: Photosynthesis converts light energy into chemical energy stored in the bonds of glucose. This is why plants are called producers: they produce organic molecules from inorganic raw materials using energy from the sun.