Major Events During Photosynthesis (Class 10 Biology)

According to the NCERT syllabus, the complex chemical process of photosynthesis occurs in three distinct, sequential events inside the chloroplasts of the plant cell:

Event 1: Absorption of Light Energy

• The green pigment present in the leaves, called Chlorophyll, traps and absorbs solar energy (sunlight) falling on the leaf.

Event 2: Conversion of Energy and Splitting of Water

• The absorbed light energy is converted into chemical energy.
• This chemical energy is immediately used to break down (split) water molecules (H₂O) absorbed from the soil into Hydrogen and Oxygen gas. (The Oxygen is released into the air as a byproduct).

Event 3: Reduction of Carbon Dioxide

• The plant takes in Carbon Dioxide (CO₂) from the air through its stomata.
• The Hydrogen created in Step 2 is added to the Carbon Dioxide. This chemical addition of hydrogen is called 'Reduction'.
• The reduction of Carbon Dioxide results in the formation of Carbohydrates (Glucose/Sugar), which is the actual food of the plant.

All these events can be summarized in one master chemical equation: 6CO₂ + 12H₂O + (Light Energy) → C₆H₁₂O₆ (Glucose) + 6O₂ + 6H₂O

Not always! In normal plants, these steps happen one after the other during the daytime. However, in Desert Plants (like Cactus), keeping the stomata open during the hot day to absorb CO₂ would cause all their water to evaporate. So, desert plants take up CO₂ at night, store it as an intermediate chemical, and wait for the sun to rise the next day to complete the remaining events.