Biological termEasy1 mark
2(i)
Name the following:
The main nitrogenous waste formed in the body.
Topic: Urea
Previous-year question practice database
Answer
Exam answer
UREA.
Explanation
Urea is the chief nitrogenous waste in humans. It is formed IN THE LIVER from excess amino acids by the ORNITHINE CYCLE, carried in the blood to the kidneys, and excreted in urine.
WHY IT MUST BE MADE: excess amino acids cannot be stored, so their amino group is removed (deamination), producing highly toxic AMMONIA. The liver at once converts it into urea, which is far less toxic and can safely travel in the blood.
The three nitrogenous wastes and who excretes them: AMMONIA (fishes, most toxic, needs much water), UREA (mammals), URIC ACID (birds and insects, least toxic, needs least water). Land animals that must conserve water excrete the least soluble waste.
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