Describe how urea is produced in the liver and then removed from the body.

Cambridge International IGCSE Biology (0610) — 13.1 Excretion in humans · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Excess amino acids are deaminated in the liver, removing the amino group and forming urea. The urea is carried in the blood to the kidneys, where it is filtered out at the glomerulus. Urea then leaves the body dissolved in urine, which travels from the kidney along the ureter to the bladder and is expelled through the urethra.

Examiner tips

  • Use the word "deaminated" to show the chemical step. Mention the liver as the site of urea formation. State that urea is transported in the blood. Describe the glomerulus as the filtering site and the ureter/bladder/urethra as the excretion route.
  • common_mistakes
  • :
  • Confusing urea formation with the urea cycle steps. Omitting the kidney filtration step. Using vague terms like "kidney" without specifying glomerulus or urine passage.

Mark scheme (4 marks)

  1. Excess amino acids cannot be stored, so they are broken down (deaminated) in the liver
  2. Deamination removes the nitrogen-containing (amino) group from the amino acid, forming urea
  3. Urea is carried in the blood to the kidney, where it is filtered out at the glomerulus
  4. Urea leaves the body dissolved in urine, which passes from the kidney along the ureter to the bladder and out through the urethra

Key terms in this question

urea

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