Question 3 of 17intermediate🔍 AnalyzeShort Answer2 marks
6CO2+12H2O→LightC6H12O6+6H2O+6O26\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow{\text{Light}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{H}_2\text{O} + 6\text{O}_2

Can you explain why twelve molecules of water as substrate are used in the equation given above?

Correct Answer

Twelve molecules of water are used as substrate in the photosynthesis equation to produce one molecule of glucose. According to the context, to make one molecule of glucose, 6 turns of the Calvin cycle are required, and the process requires 12 NADPH molecules.

The splitting of water is associated with PS II, where water splits into 2H⁺, [O], and electrons. The equation given is: 2H₂O → 4H⁺ + O₂ + 4e⁻. This means that 2 molecules of water yield 4 electrons. To generate sufficient electrons for the 12 NADPH required in the Calvin cycle, 12 molecules of water must be split. Additionally, these 12 water molecules provide the protons (H⁺) needed for the reduction process and release oxygen as a byproduct.

Exercise: 11.2 Early Experiments | Q: In-text 3 | (Page Page 5)
For More Understanding

Explanation

The question relates to the balanced photosynthesis equation. The context clearly states that 12 NADPH molecules are required to make one glucose molecule through the Calvin cycle. The water splitting equation shows that 2 H₂O molecules produce 4 electrons. Therefore, to supply enough electrons for 12 NADPH (which requires 24 electrons), 12 water molecules must be split. This is a logical deduction from the provided context about the Calvin cycle requirements and the water splitting process.

Solution Steps

  1. Step 1: From the context, making one glucose requires 12 NADPH molecules

  2. Step 2: Water splitting equation: 2H₂O → 4H⁺ + O₂ + 4e⁻ (2 water molecules yield 4 electrons)

  3. Step 3: To supply electrons for 12 NADPH, 12 water molecules are needed as substrate

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