Which of the following statements is incorrect?

Options

A. In ureotelic organisms, ammonia is not a product of metabolism.
B. In mammals, some amount of urea may be retained in the kidney matric to maintain osmalority.
C. In fish, kidneys do not play any significant role in the removal of ammonium ions.
D. Urea and uric acid are less toxic than ammonia.

Explanation

To determine which statement is incorrect regarding excretory products and their elimination, we need to analyze each statement provided in the question.

### Step-by-Step Solution:

1. **Understanding Uricotillic Organisms**:
- Uricotillic organisms primarily excrete uric acid. The statement claims that in uricotillic organisms, ammonia is not a product of metabolism. This is misleading because while uricotillic organisms excrete uric acid, ammonia is still produced as a byproduct of protein metabolism, but it is converted to uric acid for excretion.

2. **Ureotelic Organisms**:
- Ureotelic organisms, such as mammals, convert ammonia into urea through the urea cycle (ornithine cycle). The statement suggests that in ureotelic organisms, ammonia is not a product of metabolism. This is incorrect because ammonia is indeed produced during protein metabolism and is subsequently converted to urea.

3. **Mammals and Urea Retention**:
- The statement about mammals retaining some urea in the kidney matrix to maintain osmolarity is correct. This retention helps regulate osmotic balance in the body.

4. **Fish and Kidney Function**:
- The statement regarding fish indicates that their kidneys do not play a significant role in the removal of ammonium ions. This is true, as fish primarily excrete ammonia directly into the water.

5. **Toxicity of Nitrogenous Wastes**:
- The statement that urea and uric acid are less toxic than ammonia is also correct. Ammonia is highly toxic, while urea and uric acid are less so, allowing for safer storage and excretion.

### Conclusion:
The incorrect statement is the first one, which claims that in ureotelic organisms, ammonia is not a product of metabolism. This is false because ammonia is produced and then converted to urea.

### Final Answer:
The incorrect statement is: "In ureotelic organisms, ammonia is not a product of metabolism."

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