Explain why urea must be removed from the body, and describe the path urea takes from the kidney to the outside of the body.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Urea is a waste product of protein metabolism that is toxic to cells when it accumulates in the blood. The kidneys therefore remove it by excreting it into urine.
In the kidney, urea is filtered into the renal tubules and reabsorbed only partially, so it remains in the filtrate. The filtrate then becomes urine, which flows from the kidney through the ureter into the bladder. When the bladder is full, urine is expelled from the body through the urethra.
In the kidney, urea is filtered into the renal tubules and reabsorbed only partially, so it remains in the filtrate. The filtrate then becomes urine, which flows from the kidney through the ureter into the bladder. When the bladder is full, urine is expelled from the body through the urethra.
Examiner tips
- Use the word ‘toxic’ or ‘harmful’ when explaining why urea must be removed.
- Show the correct sequence: kidney → ureter → bladder → urethra.
- Mention that urea is present in the urine that is excreted.
Common mistakes
- Saying urea is harmless or not a waste product.
- Omitting the ureter or bladder from the pathway.
- Using the wrong order of organs or confusing the direction of flow.
Mark scheme (4 marks)
- Urea is toxic (to the body at higher concentrations) / a build-up of urea would cause harm to the organism
- Urea (in urine) passes from the kidney into the ureter
- Urine is stored in the bladder
- Urine leaves the body through the urethra
Key terms in this question
Related
- All Cambridge International IGCSE Biology (0610) revision notes →
- How to answer a "Explain and Describe" question →
- Decode the mark scheme abbreviations →