In living beings ammonia is converted into urea through

Options

A. arginine cycle
B. ornithine cycle
C. fumarine cycle
D. citrulline cycle

Answer

To answer the question "In living beings ammonia is converted into urea through," we will break down the process step by step:

### Step-by-Step Solution:

1. **Understanding the Context**:
- In living organisms, particularly ureotelic organisms (like humans), ammonia is a toxic byproduct of protein metabolism. To safely excrete nitrogen, ammonia must be converted into a less toxic form, which is urea.

2. **Identifying the Cycle**:
- The conversion of ammonia to urea occurs through a series of biochemical reactions known as the **Ornithine Cycle** (also called the Urea Cycle).

3. **Starting Compound**:
- The cycle begins with the formation of **carbamoyl phosphate**, which is synthesized in the mitochondria.

4. **Formation of Citrulline**:
- Carbamoyl phosphate combines with ornithine to form **citrulline**. This reaction occurs in the mitochondria.

5. **Formation of Argininosuccinate**:
- Citrulline then moves to the cytoplasm, where it combines with **aspartate** to form **argininosuccinate**.

6. **Conversion to Arginine**:
- Argininosuccinate is then cleaved to produce **arginine** and **fumarate**.

7. **Conversion to Urea**:
- Finally, arginine is converted back to ornithine, and during this conversion, ammonia is released and combines with water to form **urea**. This step is crucial as it is where the toxic ammonia is transformed into urea, which is less toxic and can be excreted safely.

8. **Cycle Continuation**:
- The ornithine is then recycled back into the cycle, allowing the process to continue.

### Conclusion:
Thus, ammonia is converted into urea through the **Ornithine Cycle**.