Final Answer:
The liver converts resulting ammonia to urea, ensuring safe elimination via urine. This process prevents ammonia toxicity, crucial for maintaining metabolic balance.
The correct answer is:
a. The nitrogen-containing amino group is removed from an amino acid.
Step-by-step explanation:
In the process of nitrogen excretion, the removal of the nitrogen-containing amino group from an amino acid is a crucial step. This occurs through a process called deamination. During deamination, enzymes break down amino acids into ammonia (_NH₃_) and a keto acid. This ammonia is toxic and needs to be further processed to avoid harm to the body.
The liver plays a central role in this process. Ammonia produced from deamination is converted into urea (_CO(NH₂)₂_) in the liver through the urea cycle. Urea is a less toxic compound that can be safely transported in the blood to the kidneys, where it is excreted in the urine. This mechanism helps the body to efficiently eliminate nitrogen waste without the risk of ammonia toxicity.
Unlike option (a), the other choices do not accurately describe the primary mechanism of nitrogen excretion. Option (b) incorrectly suggests that ammonia is stored in cells, option (c) inaccurately describes the conversion of ammonia to urea in the lymphatic system, and option (d) misrepresents the production and storage of uric acid instead of urea. Therefore, the removal of the nitrogen-containing amino group from an amino acid, as described in option (a), is the correct and essential step in the process of nitrogen excretion.