What is the primary purpose of the light-dependent reactions of photosynthesis?

• A. To convert light energy into chemical energy in the form of ATP and NADPH
• B. To produce oxygen by splitting carbon dioxide
• C. To fix carbon dioxide into glucose
• D. To break down glucose into pyruvate

Answer: (A)

Verified step by step guidance

1. Understand the context: Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy. It consists of two main stages: light-dependent reactions and light-independent reactions (Calvin cycle).
2. Identify the role of light-dependent reactions: These reactions occur in the thylakoid membranes of chloroplasts and require light energy to drive the production of ATP and NADPH, which are energy carriers.
3. Explain the mechanism: Light energy excites electrons in chlorophyll molecules, initiating a chain of reactions in the photosystems. These electrons are transferred through the electron transport chain, leading to the generation of ATP via photophosphorylation and NADPH through the reduction of NADP⁺.
4. Clarify oxygen production: During the light-dependent reactions, water molecules are split (photolysis) to provide electrons to replace those lost by chlorophyll. This process releases oxygen as a byproduct, but the primary purpose is not oxygen production.
5. Eliminate incorrect options: The light-dependent reactions do not involve fixing carbon dioxide into glucose (this occurs in the Calvin cycle) or breaking down glucose into pyruvate (this is part of cellular respiration). The correct purpose is to convert light energy into chemical energy in the form of ATP and NADPH.