Multiple Choice
Which portion of the photosynthetic apparatus absorbs light during the light reactions of photosynthesis?
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9. Photosynthesis
Light Reactions of Photosynthesis
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Which of the following represents a reactant in the light reactions of photosynthesis?
A
C\(_6\)H\(_{12}\)O\(_6\) (glucose)
B
NADP\(^+\) (nicotinamide adenine dinucleotide phosphate)
C
O\(_2\) (oxygen)
D
H\(_2\)O (water)
Verified step by step guidance1
Understand the light reactions of photosynthesis: These reactions occur in the thylakoid membranes of chloroplasts and involve the conversion of light energy into chemical energy, producing ATP and NADPH while releasing oxygen as a byproduct.
Identify the key reactants in the light reactions: The primary reactants are water (H\(_2\)O), light energy, and NADP\(^+\), which is reduced to NADPH during the process.
Analyze the role of water (H\(_2\)O): Water is split during a process called photolysis, which occurs in Photosystem II. This splitting produces electrons (to replace those lost by chlorophyll), protons (H\(^+\) ions), and oxygen (O\(_2\)) as a byproduct.
Eliminate incorrect options: C\(_6\)H\(_{12}\)O\(_6\) (glucose) is a product of the Calvin cycle, not a reactant in the light reactions. O\(_2\) is a byproduct of the light reactions, not a reactant. NADP\(^+\) is a reactant, but the question specifies H\(_2\)O as the correct answer.
Conclude that H\(_2\)O (water) is the correct answer because it is directly involved in the photolysis process, providing the electrons needed for the light reactions to proceed.
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