Excretion and the urinary system
Removing waste
- Excretion is removing the waste products of metabolism (and excess substances).
- Two main wastes leave the body:
- carbon dioxide (from respiration) — breathed out through the lungs,
- urea (made in the liver) — removed by the kidneys with excess water and ions.
Practice
Excretion is the removal of:
Excretion removes metabolic wastes such as carbon dioxide and urea (egestion removes undigested food).
Practice
Match each waste to how it leaves the body.
Carbon dioxide (from respiration) leaves via the lungs; urea (from the liver) leaves via the kidneys.
The urinary system
-
The kidneys clean the blood and make urine.
-
The urine then passes:
kidneys → ureters → bladder (stores it) → urethra → out
-
If the kidneys fail, a dialysis machine cleans the blood across a thin membrane.
Practice
Put the urine path in order.
Urine flows kidney → ureter → bladder → urethra → out.
You've got it
Key idea
- excretion = removing metabolic waste; carbon dioxide via lungs, urea + excess water/ions via kidneys
- urine path: kidney → ureter → bladder → urethra
- dialysis cleans the blood when the kidneys stop working