Ultimate source of hydrogen atoms for the synthesis of glucose is

Options

A. `H_2O`
B. NADPH
C. FADH
D. `n(CH_(2)O)`

Answer

To solve the question regarding the ultimate source of hydrogen atoms for the synthesis of glucose, we can break down the process of photosynthesis and identify the correct answer step by step.

### Step-by-Step Solution:

1. **Understanding Photosynthesis**: Photosynthesis consists of two main phases: the light reactions and the dark reactions (Calvin cycle). The light reactions occur in the thylakoid membranes, while the dark reactions occur in the stroma of the chloroplasts.

2. **Light Reactions**: During the light reactions, chlorophyll absorbs light energy, which leads to the splitting of water molecules (H2O). This process is known as photolysis. The equation for this reaction can be summarized as:
\[ 2H_2O \rightarrow 4H^+ + 4e^- + O_2 \]
Here, water is split into hydrogen ions (H+), electrons (e-), and oxygen (O2).

3. **Role of NADPH**: The electrons released from the splitting of water are used to convert NAD+ into NADPH. NADPH acts as a reducing agent and carries the hydrogen atoms to the dark reactions where glucose is synthesized.

4. **Dark Reactions**: In the dark reactions, ATP and NADPH produced from the light reactions are used to convert carbon dioxide (CO2) into glucose (C6H12O6). The hydrogen ions (H+) from NADPH are essential for this process.

5. **Identifying the Ultimate Source**: The question asks for the ultimate source of hydrogen atoms for glucose synthesis. While NADPH provides the hydrogen ions for the dark reactions, the ultimate source of these hydrogen atoms is the water (H2O) that was split during the light reactions.

6. **Conclusion**: Therefore, the ultimate source of hydrogen atoms for the synthesis of glucose is **H2O**.

### Final Answer:
The ultimate source of hydrogen atoms for the synthesis of glucose is **A. H2O**.

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