Cambridge IGCSE Biology 0610 · Topic 13.1
Excretion in Humans
This chapter follows one substance, urea, on its entire journey through the body: formed in the liver, carried in the blood, filtered inside the kidney, and finally removed in urine. Once you can hold that whole route in your head, most of what looks like several separate syllabus points turns out to be one connected story told from different angles.
Cambridge groups the whole topic under a single syllabus point, 13.1 Excretion in humans, but the exam rewards treating it as three connected jobs done by three different organs. Core candidates need to know which substances the lungs and kidneys each remove, and be able to identify the four organs of the urinary system on a diagram. Supplement candidates go further, into the internal structure of the kidney, how a nephron filters and then selectively reabsorbs substances to build urine, and how the liver deals with excess amino acids through deamination to produce the urea the kidneys are removing in the first place.
Students tend to lose marks here less because they don’t know the biology, and more because they blur two ideas Cambridge deliberately keeps separate: forming a substance is not the same as excreting it, and filtering a substance out of the blood is not the same as it ending up in urine. “The kidney cleans the blood” sounds reasonable, but it isn’t the answer a mark scheme is built around — the pages below are written to give you the actual causal chain instead.
What’s in this chapter
| Page | Level | What it covers |
|---|---|---|
| What is excretion? | Core | Which substances the lungs and kidneys actually remove, why excretion isn’t the same as egestion, and why the liver forming urea and the kidneys excreting it are two separate jobs. |
| The human urinary system | Core | Kidneys, ureters, bladder and urethra, in the order urine actually travels through them — and the one letter that separates a ureter from a urethra. |
| Kidney and nephron | Supplement | Cortex, medulla, and the filter-then-recover system inside a nephron that explains why useful glucose ends up back in your blood instead of your urine. |
| Deamination and urea | Supplement | How the liver strips the nitrogen-containing part off spare amino acids to make urea, and why that urea can’t be left to build up in the body. |
Core or Supplement?
The first two pages — what excretion actually is, and the four organs of the urinary system — are Core, so every candidate needs them regardless of tier. The kidney and nephron page and the deamination and urea page are both Supplement only, required for the Extended paper and not for Core-only candidates. If you’re not sure which tier you’re sitting, that’s worth checking before you spend time on either Supplement page, since neither one is needed to answer a Core-level question.