CBSE Class 10 Answered

Light reaction is an energy trapping, photochemical reaction, taking place in the grana of chloroplast and resulting in the formation of ATP and NADPH_2. During light reaction, chlorophyll absorbs energy, gets excited and releases a high energy electron which passes through a system of electron acceptors. During this electron transfer, energy is released in the form of ATP.

In dark reaction, CO₂ is reduced to -arbohydrates. This reaction takes place in stroma of chloroplasts. It is independent of light. Here, ATP and NADPH₂ is utilized.

In light reaction, there are 2 pathways of electron transfer, which are cyclic and non-cyclic electron transfer. During non-cyclic electron transfer, photolysis of water takes place. Under the influence of light, water molecule splits into H⁺ and OH^-. Photolysis results in the generation of free oxygen (O₂). This process is responsible for generating the majority of breathable oxygen in earth's atmosphere.