The nitrogenous excrtory products are formed from the catabolism of amino acids by

Options

A. Calvin cycle
B. Nitrogen cycle
C. Ornithine cycle
D. Krebs cycle

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the cycle responsible for the formation of nitrogenous excretory products from the catabolism of amino acids.

2. **Identifying the Relevant Cycle**: The urea cycle, also known as the ornithine cycle, is the metabolic pathway that converts ammonia, which is a toxic byproduct of amino acid catabolism, into urea, a less toxic compound that can be excreted from the body.

3. **Process of Amino Acid Catabolism**: When proteins are broken down, they yield amino acids. These amino acids undergo deamination, a process where the amino group is removed, resulting in the formation of ammonia.

4. **Formation of Urea**: The ammonia produced from deamination combines with carbon dioxide in the liver, facilitated by carbamoyl phosphate, to form citrulline. This citrulline then undergoes several transformations through the urea cycle, eventually leading to the production of urea.

5. **Conclusion**: The cycle that facilitates the conversion of ammonia into urea, thereby forming nitrogenous excretory products, is the urea cycle or ornithine cycle.

6. **Final Answer**: The nitrogenous excretory products are formed from the catabolism of amino acids by the **urea cycle (ornithine cycle)**.