AQA GCSE Biology (8461), Higher tier · Homeostasis and response › Hormonal coordination in humans
Practise Maintaining water and nitrogen balance. 14 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Name the organs that remove excess water, ions and urea from the body in urine.
Kidneys
The control of the water content of the blood by ADH is an example of negative feedback. What is meant by negative feedback?
A change from the normal level causes a response that reverses the change
Explain why ammonia is converted into urea immediately after it is made.
Ammonia is toxic
Name the hormone that acts on the kidney tubules to control the water level in the body.
ADH
Name the process by which urea moves from the blood into the dialysis fluid.
Diffusion
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy6 marks
Water, ions and urea are lost from the body in several ways.
(a) Which two organs lose water from the body with no control over the amount of water lost? Tick (✓) two boxes.[2]
Kidneys
Liver
Lungs
Pancreas
Skin
(b) Name the organs that remove excess water, ions and urea from the body in urine.[1]
(c) Which substances are lost from the skin in sweat? Tick (✓) one box.[1]
Glucose, ions and water
Ions, urea and water
Protein, urea and water
Water only
(d) Explain why it is important that body cells do not lose or gain too much water.[2]
Show the answer and mark scheme
(a)Answer: Lungs; Skin
(b)Answer: Kidneys
kidneys
(c)Answer: Ions, urea and water
(d)Answer: Water moves into or out of cells by osmosis; if cells gain or lose too much water they do not function efficiently (they may swell and burst or shrink)
water moves into / out of cells by osmosis
cells do not function efficiently / cells may burst or shrink
Question 2Medium8 marks
The water content of the blood is controlled by the hormone ADH.
(a) Which gland releases ADH? Tick (✓) one box.[1]
Adrenal gland
Pancreas
Pituitary gland
Thyroid gland
(b) A student ran a long race on a hot day and did not drink any water. Explain how ADH helps to keep the water content of the student's blood within normal limits.[3]
(c) After the race the student drank 2 dm³ of water. Describe and explain how the student's urine would change.[3]
(d) The control of the water content of the blood by ADH is an example of negative feedback. What is meant by negative feedback?[1]
Show the answer and mark scheme
(a)Answer: Pituitary gland
(b)Answer: Water lost in sweat makes the blood too concentrated, so the pituitary gland releases more ADH; ADH makes the kidney tubules reabsorb more water into the blood, so a small volume of concentrated urine is produced
water is lost in sweat so the blood becomes too concentrated
the pituitary gland releases more ADH (into the blood)
ADH causes the kidney tubules to reabsorb more water (into the blood)
(so) a small volume of concentrated urine is produced
(c)Answer: The blood becomes too dilute, so less ADH is released and less water is reabsorbed by the kidney tubules, so a large volume of dilute urine is produced
the blood becomes too dilute / the water content of the blood increases
less ADH is released (by the pituitary gland)
less water is reabsorbed (by the kidney tubules)
(so) a large volume of dilute urine is produced
(d)Answer: A change from the normal level causes a response that reverses the change
a change (in a level) causes a response that reverses the change / returns the level to normal
Question 3Hard9 marks
Proteins in the diet are digested into amino acids. Excess amino acids cannot be stored in the body and must be removed safely.
(a) Describe how excess amino acids are converted into urea. Name the organ where this happens.[3]
(b) Explain why ammonia is converted into urea immediately after it is made.[1]
(c) A man ate a diet containing 150 g of protein per day for two weeks. He then ate a diet containing 50 g of protein per day for two weeks. The mean mass of urea in his urine was 42 g per day on the first diet and 15 g per day on the second diet. Calculate the percentage decrease in the mass of urea excreted per day. Give your answer to 3 significant figures.[2]
(d) Explain why the mass of urea excreted decreased on the second diet.[2]
(e) Suggest why the man still excreted urea on the low-protein diet.[1]
Show the answer and mark scheme
(a)Answer: In the liver, amino acids are deaminated to form ammonia, which is immediately converted into urea
in the liver
amino acids are deaminated
(forming) ammonia
(ammonia is) converted to urea
(b)Answer: Ammonia is toxic
ammonia is toxic / poisonous
(c)Answer: 64.3%
(42 − 15) ÷ 42 × 100
64.3 (%)
(d)Answer: Less protein means fewer excess amino acids, so less deamination in the liver and less urea made
less protein eaten so fewer excess amino acids
(so) less deamination / less ammonia made, so less urea is produced (and excreted)
(e)Answer: Some amino acids were still in excess / proteins in the body are constantly broken down
some amino acids were still in excess (of the body's needs) / body proteins are broken down and the amino acids deaminated