The Urinary System and Urea

1. 1 State [1 mark]

   State the organ in which urea is made.

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   Model answer

   The liver.

   Mark scheme

   • Liver — 1 mark
2. 2 Name [2 marks]

   Name the tube that carries urine from the kidney to the bladder, and the tube that carries urine out of the body.

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   Model answer

   The ureter carries urine from the kidney to the bladder, and the urethra carries it out of the body.

   Mark scheme

   • Ureter — 1 mark
   • Urethra — 1 mark
3. 3 Describe [3 marks]

   Describe how urea is made in the body.

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   Model answer

   Excess amino acids that are not needed to make proteins are broken down in the liver. The nitrogen in them is converted into urea. The urea is released into the blood.

   Mark scheme

   • Excess amino acids are broken down — 1 mark
   • In the liver — 1 mark
   • Urea is released into the blood — 1 mark
4. 4 Explain [2 marks]

   Explain why urea must be removed from the blood.

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   Model answer

   Urea is a toxic waste product. If it builds up in the blood, it can damage the cells and the body.

   Mark scheme

   • Toxic — 1 mark
   • Builds up and damages cells — 1 mark
5. 5 Explain [3 marks]

   Explain why the blood in the renal vein has less urea than the blood in the renal artery.

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   Model answer

   The kidney filters the blood. The urea is removed from the blood in the kidney, and leaves the body in the urine. So the blood that leaves the kidney in the renal vein has little urea.

   Mark scheme

   • The kidney filters the blood — 1 mark
   • Urea removed from the blood — 1 mark
   • Leaves in the urine — 1 mark
6. 6 Evaluate [6 marks]

   Describe the path of urea from the cells of the body to the outside of the body, and explain why it is important that urea is removed.

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   Model answer

   Excess amino acids are broken down in the liver, which makes ammonia and then urea. The urea is released into the blood plasma, and carried to the kidneys in the renal artery. The kidneys filter the urea out of the blood, and it is part of the urine, which is carried down the ureters to the bladder, where it is stored. The urine leaves the body through the urethra. The blood that leaves the kidney in the renal vein has little urea. It is important to remove urea because it is toxic, and it would damage the cells and the body if it built up in the blood.

   Mark scheme

   • Amino acids broken down in the liver — 1 mark
   • Urea released into the blood — 1 mark
   • Carried to the kidney — 1 mark
   • Filtered out, in urine — 1 mark
   • Ureter, bladder, urethra — 1 mark
   • Toxic if it builds up — 1 mark

Quick check

1. 1

   Where is urea made?

   1. AIn the kidney
   2. BIn the bladder
   3. CIn the liver
   4. DIn the lungs
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   C: In the liver

   In the liver, from excess amino acids.

2. 2

   What is urea made from?

   1. AExcess glucose
   2. BExcess amino acids
   3. CExcess fat
   4. DExcess water
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   B: Excess amino acids

   Excess amino acids.

3. 3

   Which organ stores urine?

   1. AThe kidney
   2. BThe ureter
   3. CThe urethra
   4. DThe bladder
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   D: The bladder

   The bladder.

4. 4

   What does the ureter do?

   1. ACarries urine from the kidney to the bladder
   2. BCarries urine out of the body
   3. CStores urine
   4. DMakes urea
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   A: Carries urine from the kidney to the bladder

   It carries urine from the kidney to the bladder.

5. 5

   What does the urethra do?

   1. ACarries blood to the kidney
   2. BCarries urine out of the body
   3. CFilters the blood
   4. DMakes urine
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   B: Carries urine out of the body

   It carries urine from the bladder out of the body.

6. 6

   Which vessel carries blood into the kidney?

   1. AThe renal vein
   2. BThe ureter
   3. CThe renal artery
   4. DThe urethra
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   C: The renal artery

   The renal artery.

7. 7

   Why must urea be removed from the body?

   1. AIt is toxic
   2. BIt is a source of energy
   3. CIt is needed in the blood
   4. DIt is a hormone
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   A: It is toxic

   It is toxic.

8. 8

   Which blood vessel has the lowest concentration of urea?

   1. AThe hepatic vein
   2. BThe renal artery
   3. CThe vena cava before the kidney
   4. DThe renal vein
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   D: The renal vein

   The renal vein, because the kidney has filtered the blood.

9. 9

   Which of these is NOT part of the urinary system?

   1. AThe bladder
   2. BThe pancreas
   3. CThe ureter
   4. DThe kidney
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   B: The pancreas

   The pancreas is not part of the urinary system.