Fiducia TogetherThe kidneys and the liver
Two organs that clean and regulate. Filtration, reabsorption and deamination.
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.
What it is
The kidneys filter the blood, reabsorbing useful substances and producing urine. The liver deals with excess amino acids by deamination, producing urea, and breaks down toxins including alcohol.
Where it applies
GCSE biology and combined science.
How it works
Filtration is non-selective: small molecules including glucose, water, ions and urea pass into the tubule. Selective reabsorption then takes back all the glucose, the water needed and the ions needed. Urea is not reabsorbed.
ADH controls how much water is reabsorbed, which is the homeostasis link.
How to use it in your work
Say 'selective' reabsorption and name what is reabsorbed. Listing glucose, some water and some ions is the mark.
Urea is produced in the LIVER and excreted by the kidneys. Getting that the wrong way round is a common and costly error.
Where to get help
Your teacher, your board's specification for the depth required at your tier, and Bitesize for the diagrams.
Revise this with a song
These are ours. We write revision songs because a lot of people remember a tune when they cannot remember a page, and because revising out loud in the kitchen beats staring at a highlighter.
- The Biology Song The GCSE biology specification, set to music.
Where to read more
Last reviewed 2026-08-28 by Fiducia Together · Next review due 2027-08-28
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.