UreaSpec 7.22B
In short
Urea is a waste substance made in the liver when excess amino acids are broken down, because the body cannot store them. It is carried in the blood to the kidneys, which remove it from the blood in the urine. Remember that urea is made from amino acids, not from glucose or fat.
The body cannot store excess amino acids. They are broken down in the liver, and urea is produced. Urea is a waste substance. It is carried in the blood to the kidneys and removed in the urine.
Exam tip:Write ‘urea is made in the liver from excess amino acids’. It is made from amino acids, not from glucose or fat.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026
Frequently asked questions
How does the kidney filter blood?
The kidney filters blood in its many nephrons. In each nephron, blood in the glomerulus is at high pressure, so small molecules such as water, glucose, urea and ions are forced out into the Bowman's capsule. Proteins and blood cells are too large and stay in the blood. Useful substances are then reabsorbed.
Why is there no glucose in urine?
There is no glucose in the urine of a healthy person because it is all reabsorbed in the nephron. Glucose is small, so it is filtered out of the blood at the glomerulus into the Bowman's capsule. In the first part of the tubule, all of it is reabsorbed into the blood by active transport, which uses energy from respiration.
What does ADH do in the kidneys?
Higher tier ADH makes the collecting ducts of the kidneys more permeable to water, so more water is reabsorbed into the blood. The pituitary gland releases more ADH when the blood water content is too low, so a small volume of concentrated urine is made. When the water content is too high, less ADH is released and the urine is dilute.
All 4 questions on The urinary system and the kidneys
