Describe the journey of urea from its site of production to its removal from the body in urine.

Eduqas A-Level Biology — 3.7 Homeostasis and the kidney · Describe · 5 marks · View as Markdown

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

Urea is a waste product that must be removed from the body. It is produced when excess amino acids are broken down.

Model answer (5 marks)

Urea is produced in the liver by the urea cycle.
It is released into the bloodstream and carried to the kidneys.
In the glomerulus it is filtered into the renal tubules.
Urea then diffuses into the tubular fluid, becoming part of the urine.
The urine travels via the ureters to the bladder and is expelled through the urethra.

Examiner tips

Use the exact sequence of organs (liver → blood → kidney → urine → bladder → urethra).
Show that urea is filtered, not reabsorbed, in the kidneys.
Mention the transport of urea in the blood.
Keep the answer concise and in correct order.

Common mistakes

Confusing the liver with the kidneys as the site of production.
Saying urea is secreted rather than filtered.
Omitting the ureters or bladder in the final excretion step.

Mark scheme (5 marks)

Urea is produced in the liver
Urea passes into the bloodstream / is transported in the blood to the kidneys
Urea is filtered out of the blood in the kidneys
Urea passes into the urine / is dissolved in water to form urine
Urine passes from the kidneys through the ureter to the bladder and is excreted via the urethra

Key terms in this question

urea · urine