Describe the process of photosynthesis. Write the overall chemical equation of photosynthesis.

Photosynthesis is the biological process by which green plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen. It occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin Cycle).

Process of Photosynthesis

1. Light Absorption

   • Chlorophyll (the green pigment in chloroplasts) and other accessory pigments (carotenoids, xanthophylls) absorb light energy, primarily from blue (400–500 nm) and red (600–700 nm) wavelengths.
   • This energy excites electrons in chlorophyll, initiating the process.

2. Light-Dependent Reactions (Photochemical Phase)

   • Occur in the thylakoid membranes of chloroplasts.
   • Photolysis of Water: Water molecules are split into oxygen (O₂), protons (H⁺), and electrons (e⁻). $$2H_{2}O\stackrel{\text{light}}{\to }4H^{+}+4e^{-}+O_2$$
   • ATP Formation: The excited electrons move through the electron transport chain, generating a proton gradient that drives ATP synthesis via chemiosmosis.
   • NADPH Formation: Electrons are transferred to NADP⁺, forming NADPH (an energy carrier).

3. Light-Independent Reactions (Calvin Cycle / Dark Reactions)

   • Occur in the stroma of chloroplasts.
   • Carbon Fixation: CO₂ is attached to a 5-carbon sugar (RuBP) by the enzyme RuBisCO, forming an unstable 6-carbon compound that splits into two 3-carbon molecules (3-PGA).
   • Reduction Phase: ATP and NADPH from the light reactions provide energy to convert 3-PGA into G3P (glyceraldehyde-3-phosphate), a sugar precursor.
   • Regeneration of RuBP: Some G3P molecules are used to regenerate RuBP, while others combine to form glucose (C₆H₁₂O₆) and other carbohydrates.

Overall Chemical Equation of Photosynthesis

The balanced chemical equation representing the entire process is: $$6C{O}_2+6H_{2}O+\text{light energy}\stackrel{\text{chlorophyll}}{\to }{C}_6{H}_{12}{O}_6+6O_2$$

• Reactants: Carbon dioxide (CO₂) and water (H₂O) in the presence of sunlight.
• Products: Glucose (C₆H₁₂O₆, a carbohydrate) and oxygen (O₂, a byproduct).

Carbon dioxideCarbon dioxide

This process is fundamental to life on Earth, as it produces oxygen and forms the base of the food chain.