The kidney: GCSE Biology
Nephrons, ultrafiltration, selective reabsorption, ADH, dialysis and transplants
The short version
Nephrons filter blood at the glomerulus, reabsorb useful substances, and ADH controls how much water is kept.
Key idea
Grade 2–3: Two kidneys, a bag in the middle, a tube out.
Grade 5–6: I can order ureter then urethra and say urea is a waste.
Grade 9: I mention liver making urea (deamination) and kidney as the effector for water balance.
Go a bit deeper
Proteins and cells do not pass
Grade 2–3: The knot of tubes pushes the watery waste out but keeps the blood cells in.
Grade 5–6: I can name glomerulus and say proteins stay in the blood.
Grade 9: I use "ultrafiltration" at the glomerulus, list small vs large, and I never say urea is reabsorbed completely.
Worked example
Worked example
Grade 2–3: Two kidneys, a bag in the middle, a tube out. Grade 5–6: I can order ureter then urethra and say urea is a waste. Grade 9: I mention liver making urea (deamination) and kidney as the effector for water balance.
Lessons in this topic
- The urinary system
- The nephron and ultrafiltration
- Selective reabsorption
- ADH and water balance
- Kidney failure
- Dialysis vs transplant
In the app each lesson is video (when we have a real YouTube id) then intro, learn and summary steps.
What the examiner wants
Describe ultrafiltration and selective reabsorption, explain ADH negative feedback, and compare dialysis with transplant.
Try these questions
Cover the answers and have a go first. Worked solutions are underneath.
Urea is made in the
Urine leaves the kidney through the
Ultrafiltration happens at the
Which does NOT normally pass into the filtrate?
Common mistakes
- Ureter and urethra are not the same word. Mixing them is a 0 on a 1-mark label.
- Ultrafiltration is not selective reabsorption and it is not ADH. Wrong named process, wrong place.
- Selective reabsorption is not "the glomerulus choosing". The glomerulus filters by size; the tubule chooses what to take back.
- ADH does not "add water from the bladder into the blood". Water is reabsorbed from the nephron into the blood.
Answers and working
Frequently asked questions
Is GCSE The kidney on Combined Science and Triple?
The kidney is Triple-only Biology. Combined Science students can skip it.
Which exam board is this The kidney page for?
The ideas are board-agnostic for AQA, Edexcel, OCR, WJEC and CCEA. Paper lengths and question numbers differ — check your specification.
Is The kidney Foundation or Higher?
The core ideas appear on both tiers. Higher papers add extra application and some HT-only detail, marked in lessons with a Higher badge.
Learn, try, get feedback, fix the mistake
Open the stepped lesson, then the quiz with hints. Required-practical and calculation questions use the same method you will need in the paper.
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