Question

multiple choice 2 point
the chemical reaction for photosynthesis is 6co₂ + 12h₂o + light energy c₆h₁₂o₆ + 6o₂ + 6h₂o
in the input water is labeled with a radioactive isotope of oxygen, ¹⁸o, then the oxygen gas released as the reaction proceeds is also labeled with ¹⁸o. which of the following is the most likely explanation?
during the light reactions of photosynthesis, water is split, the hydrogen atoms combine with the co₂, and oxygen gas is released.
during the light reactions of photosynthesis, water is split, removing electrons and protons, and oxygen gas is released.
during the calvin cycle, water is split, regenerating nadph from nadp+, and oxygen gas is released.
during the calvin cycle, water is split, the hydrogen atoms are added to intermediates of sugar synthesis, and oxygen gas is released.
multiple choice 2 point
which of the following is a process in which carbon from carbon dioxide is incorporated into organic molecules
calvin cycle (light - independent reactions of photosynthesis)

Explanation:

• In photosynthesis, during the light reactions, water (\(H_2O\)) is split. The hydrogen atoms (\(H\)) from water combine with \(CO_2\) in the Calvin cycle (light - independent reactions) to form organic molecules (like glucose). The oxygen (\(O\)) from water is released as \(O_2\) gas.
• Let's analyze each option:
• Option 1: During the light reactions of photosynthesis, water is split, the hydrogen atoms combine with the \(CO_2\), and oxygen gas is released. This is correct because the oxygen in the released \(O_2\) comes from water.
• Option 2: During the light reactions of photosynthesis, water is split, removing electrons and protons, and oxygen gas is released. This is incorrect as it does not mention the combination of hydrogen with \(CO_2\) which is part of the overall photosynthesis process related to the input water labeling.
• Option 3: During the Calvin cycle, water is split, regenerating NADPH from \(NADP^+\), and oxygen gas is released. This is incorrect because water is not split in the Calvin cycle. The Calvin cycle uses \(CO_2\) and the products of the light reactions (\(ATP\) and \(NADPH\)).
• Option 4: During the Calvin cycle, water is split, the hydrogen atoms are added to intermediates of sugar synthesis, and oxygen gas is released. This is incorrect as water is not split in the Calvin cycle.

Answer:

During the light reactions of photosynthesis, water is split, the hydrogen atoms combine with the \(CO_2\), and oxygen gas is released.