Excretion and the kidneys Cambridge IGCSE Biology (9–1) revision
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In plain words
Your cells make waste as they work, and it has to go before it poisons you. Carbon dioxide leaves through the lungs. The kidneys deal with the rest: they filter the blood, take back everything useful, and send the leftovers to the bladder as urine.
Three things to know
- The lungs excrete carbon dioxide. The kidneys excrete urea and any excess water and ions, as urine. Urea is made in the liver from amino acids the body doesn't need.
- Urine goes from each kidney down a ureter to the bladder, where it is stored, and leaves through the urethra.
- In the kidney, small molecules (water, glucose, urea, ions) are filtered out of the blood. Then all of the glucose, most of the water and some ions are reabsorbed back into the blood. What stays behind is urine.
Tips and tricks
- Ureter (two of them, kidney to bladder) and urethra (one, bladder to outside) are easy to mix up. The longer word is the shorter tube.
- Glucose in the urine is a sign of diabetes: a healthy kidney takes all of it back.
It lands in your notebook with its questions as flashcards.
Excretion and the kidneys: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which organ makes urea?
It is made from amino acids the body can't store.
Which tube carries urine from a kidney to the bladder?
There are two, one from each kidney.
What is excreted by the lungs?
It is a waste product of respiration.
What happens to glucose that is filtered in the kidney?
The body needs it for respiration.
What does urine contain?
Proteins and blood cells are too big to be filtered.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 8 marks. Write your answers on paper, then check them.
Excretion and the kidneys
Cambridge IGCSE Biology (9–1) 0970 · 8 marks · papermunch.org
Name ______________________________ Date ______________
Name the three main substances that the kidneys remove from the blood.[3]
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Urea, excess water and excess ions (salts).
State where urea is made and what it is made from.[2]
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In the liver, from excess amino acids.
Explain why the urine of a healthy person contains urea but no glucose.[3]
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Both are filtered out of the blood. All of the glucose is reabsorbed into the blood because the body needs it; urea is a waste product and is not reabsorbed.
Answers: Excretion and the kidneys
- 1. Urea, excess water and excess ions (salts).
- 2. In the liver, from excess amino acids.
- 3. Both are filtered out of the blood. All of the glucose is reabsorbed into the blood because the body needs it; urea is a waste product and is not reabsorbed.