In which one of the following do the two names refer to one and the same thing

Options

A. Citric acid cycle and Calvin cycle
B. Krebs' cycle and Calvin cycle
C. TCA cycle and urea cycle
D. Tricarboxylic acid cycle and citric acid cycle

Answer

To solve the question "In which one of the following do the two names refer to one and the same thing?", we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding the Terms**:
- We need to identify what each term refers to in the context of biological cycles.
- The terms in question are:
- Citric Acid Cycle
- Calvin Cycle
- Krebs Cycle
- TCA Cycle
- Urea Cycle
- Tricarboxylic Acid Cycle

2. **Analyzing Each Option**:
- **Option A: Citric Acid Cycle and Calvin Cycle**:
- The Citric Acid Cycle (also known as the Krebs Cycle or TCA Cycle) is involved in cellular respiration and occurs in mitochondria.
- The Calvin Cycle is part of photosynthesis in plants and involves the fixation of carbon dioxide.
- **Conclusion**: These are different processes. **Not the same**.

- **Option B: Krebs Cycle and Calvin Cycle**:
- The Krebs Cycle is synonymous with the Citric Acid Cycle and is involved in energy production.
- The Calvin Cycle is involved in photosynthesis.
- **Conclusion**: These are different processes. **Not the same**.

- **Option C: TCA Cycle and Urea Cycle**:
- The TCA Cycle (Tricarboxylic Acid Cycle) is the same as the Krebs Cycle and is involved in energy production.
- The Urea Cycle is a process that converts ammonia to urea in ureotelic organisms.
- **Conclusion**: These are different processes. **Not the same**.

- **Option D: Tricarboxylic Acid Cycle and Citric Acid Cycle**:
- The Tricarboxylic Acid Cycle is another name for the Citric Acid Cycle and is also known as the Krebs Cycle.
- **Conclusion**: These terms refer to the same cycle. **They are the same**.

3. **Final Answer**:
- The correct answer is **Option D: Tricarboxylic Acid Cycle and Citric Acid Cycle** refer to one and the same thing.