(a) The conversion of a protein waste, the ammonia into urea/ornithine cycle occurs in
(b) Urea is synthesised in

Options

A. Kidneys
B. Lungs
C. Intestine
D. Liver

Answer

### Step-by-Step Solution:

**(a)** The conversion of protein waste, ammonia, into urea occurs in the liver through a process known as the urea cycle or ornithine cycle.

1. **Understanding Protein Metabolism**: Proteins are made up of amino acids, which contain nitrogen. When proteins are metabolized, nitrogen is released in the form of ammonia.

2. **Toxicity of Ammonia**: Ammonia is highly toxic and requires a significant amount of water to be excreted from the body.

3. **Conversion to Urea**: To safely eliminate nitrogen from the body, ammonia is converted into urea, which is less toxic.

4. **Location of Conversion**: This conversion occurs primarily in the liver, where a series of enzymatic reactions take place. Some reactions occur in the mitochondria of liver cells, while others occur in the cytosol.

5. **Conclusion for Part (a)**: Therefore, the correct answer for where the conversion of ammonia into urea occurs is the **liver**.

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**(b)** Urea is synthesized in the liver.

1. **Synthesis Process**: As mentioned, the urea cycle in the liver is responsible for converting ammonia into urea.

2. **Transport of Ammonia**: Ammonia produced from protein metabolism is transported to the liver, where it undergoes conversion.

3. **Final Product**: The end product of this cycle is urea, which is then released into the bloodstream.

4. **Conclusion for Part (b)**: Thus, the correct answer for where urea is synthesized is also the **liver**.

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### Summary of Answers:
(a) The conversion of ammonia into urea occurs in the **liver**.
(b) Urea is synthesized in the **liver**.

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