OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What waste product is formed from the conversion of excess amino acids?

1. Urea

2. Ammonia

3. Creatinine

4. Carbon dioxide

The correct answer is: Urea

The waste product formed from the conversion of excess amino acids is urea. In the process of amino acid metabolism, when there is an excess of amino acids in the body, they undergo deamination, a process that removes the amino group. This amino group is converted into ammonia, which is highly toxic. To safely excrete this ammonia, the liver converts it into urea through the urea cycle. Urea is far less toxic than ammonia and can be efficiently transported in the blood to the kidneys, where it is excreted in the urine. While ammonia is also a related byproduct from the initial deamination process, it is not excreted directly; rather, it is quickly transformed into urea to prevent toxicity. Creatinine is a waste product that arises from the normal breakdown of muscle creatine and is not directly related to amino acid metabolism. Carbon dioxide is a byproduct of cellular respiration, which involves the oxidation of glucose and other substrates, but it does not relate to the processing of amino acids. Thus, urea is the key waste product that results from the conversion of excess amino acids, highlighting its essential role in nitrogen waste management in the body.