Path of dark reaction of photosynthesis was traced through the use of

Options

A. `.^(32)P`
B. `.^(14)CO_(2)`
C. `.^(18)O_(2)`
D. X-rays.

Answer

To determine the path of the dark reaction of photosynthesis, we need to identify the specific isotope that was used in the experiments to trace this process. The dark reaction, also known as the Calvin cycle, is a crucial part of photosynthesis that occurs in the stroma of chloroplasts.

### Step-by-Step Solution:

1. **Understand the Dark Reaction**: The dark reactions of photosynthesis, primarily known as the Calvin cycle, do not require light directly. Instead, they utilize the products of the light reactions (ATP and NADPH) to convert carbon dioxide into glucose.

2. **Identify the Key Components**: The main substrate for the dark reactions is carbon dioxide (CO2). The Calvin cycle involves the fixation of carbon dioxide into organic molecules.

3. **Recognize the Isotopes Used**: To trace the path of carbon in the dark reactions, scientists use isotopes of carbon. The most commonly used isotope for this purpose is carbon-14 (C-14).

4. **Evaluate the Options**: The question provides several options: phosphorus-32, carbon dioxide-14, oxygen-18, and X-rays. Among these, carbon dioxide-14 (which implies the use of carbon-14 isotope) is the most relevant for tracing the dark reactions.

5. **Conclude the Answer**: Since the dark reactions involve the fixation of carbon dioxide and carbon-14 is specifically used to trace carbon pathways, the correct answer to the question is carbon dioxide-14.

### Final Answer:
The path of the dark reaction of photosynthesis was traced through the use of carbon dioxide-14 (C-14).