Are light reactions light dependent or light independent?

Are light reactions light dependent or light independent?

• A. Light dependent
• B. Light independent
• C. Both
• D. Neither

Answer: (A)

Light-dependent reactions require light energy. Photons absorbed by chlorophyll and other pigments energize electrons in the photosystems, driving the electron transport chain in the thylakoid membranes. This energy enables water to be split, releasing electrons and oxygen, creates a proton gradient, and powers ATP synthase to make ATP while NADP+ is reduced to NADPH. Without light, the pigments can’t be excited, the electron flow stops, no proton gradient forms, and no ATP or NADPH is produced, so these reactions cannot proceed. The other stage of photosynthesis uses the ATP and NADPH from these light reactions and can operate with or without light, provided those energy carriers are available. So the light reactions are light dependent.

Light-dependent reactions require light energy. Photons absorbed by chlorophyll and other pigments energize electrons in the photosystems, driving the electron transport chain in the thylakoid membranes. This energy enables water to be split, releasing electrons and oxygen, creates a proton gradient, and powers ATP synthase to make ATP while NADP+ is reduced to NADPH. Without light, the pigments can’t be excited, the electron flow stops, no proton gradient forms, and no ATP or NADPH is produced, so these reactions cannot proceed. The other stage of photosynthesis uses the ATP and NADPH from these light reactions and can operate with or without light, provided those energy carriers are available. So the light reactions are light dependent.