Question

Discuss the light reaction of photosynthesis.

Answer 1

Photosynthesis

Photosynthesis is a process that takes place in chloroplast, by which an organism can make food i.e. carbohydrates from CO₂ & H₂O with the help of sunlight and chlorophyll.

$6{\mathrm{CO}}_2+6{\mathrm{H}}_2\mathrm{O}\stackrel{\mathrm{Sunlight}\&\mathrm{Chlorophyll}}{\to }{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6+6{\mathrm{O}}_2$

Photosynthesis occurs in two phase:

• Light reaction
• Dark reaction

Light Reaction

• It takes place in the thylakoid present within the chloroplasts, where there are two types of photosystems that act as the reaction center.
• Light energy is absorbed which helps in the excitation of electrons.
• The electrons undergo two electron transport chains, which results in the generation of ATP (Adenosine tri-phosphate) and NADPH (Nicotinamide adenine dinucleotide phosphate).
• Photolysis of water i.e. splitting of water molecule follows, which is required to balance the electrons lost during the electron transport chain and thus, oxygen is formed.

The chemical equation in the light reaction of photosynthesis is:

2H₂O + 2NADP+ + 3ADP + 3Pi → O₂ + 2NADPH + 3ATP