Which of the following does not occur during the light reactions of photosynthesis?
a. Water is released.
b. Electrons from chlorophyll are moved to a higher-energy state by light.
c. ATP is produced.
d. NADPH is produced to carry electrons to the light-independent reactions.
e. Oxygen is produced when water is split.

Verified step by step guidance

Understand the light reactions of photosynthesis: These occur in the thylakoid membranes of chloroplasts and involve the absorption of light energy to drive the production of ATP and NADPH, while splitting water molecules to release oxygen.

Review the key processes in the light reactions: (1) Photolysis of water produces oxygen, protons, and electrons; (2) Light excites electrons in chlorophyll, raising them to a higher energy state; (3) The excited electrons move through the electron transport chain, leading to the production of ATP via chemiosmosis and NADPH via reduction of NADP⁺.

Analyze each option: (a) Water is released—this is incorrect because water is not released; instead, water is split (photolysis) to produce oxygen, electrons, and protons. (b) Electrons from chlorophyll are moved to a higher-energy state by light—this is correct and occurs during the light reactions. (c) ATP is produced—this is correct and occurs via photophosphorylation. (d) NADPH is produced to carry electrons to the light-independent reactions—this is correct and occurs during the light reactions. (e) Oxygen is produced when water is split—this is correct and occurs during photolysis.

Identify the option that does not occur: Based on the analysis, option (a) 'Water is released' does not occur during the light reactions, as water is split rather than released.

Conclude that the correct answer is the process that does not align with the light reactions, which is the release of water (option a).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Light Reactions of Photosynthesis

The light reactions of photosynthesis occur in the thylakoid membranes of chloroplasts, where sunlight is captured by chlorophyll. This energy is used to split water molecules, releasing oxygen, and to generate ATP and NADPH, which are essential for the subsequent light-independent reactions.

Water Splitting

During the light reactions, water molecules are split in a process called photolysis. This reaction produces oxygen as a byproduct and provides electrons that replace those lost by chlorophyll when it absorbs light energy, thus sustaining the photosynthetic process.

Energy Carriers: ATP and NADPH

ATP and NADPH are the primary energy carriers produced during the light reactions. ATP provides the energy needed for various cellular processes, while NADPH serves as a reducing agent, carrying high-energy electrons to the Calvin cycle, where carbon fixation occurs.