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Exam questions · Biology · The Kidneys

The Nephron and the Formation of Urine

  • 6 exam questions
  • 17 marks
  • 9 quick checks
  1. 1 State [1 mark]

    State where the blood is filtered in a nephron.

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    Model answer

    In the glomerulus and Bowman's capsule.

    Mark scheme

    • Glomerulus and capsule — 1 mark
  2. 2 Name [2 marks]

    Name two substances that are found in the blood but not in the filtrate.

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    Model answer

    Blood cells and proteins.

    Mark scheme

    • Blood cells — 1 mark
    • Proteins — 1 mark
  3. 3 Explain [3 marks]

    Explain why blood cells are not found in the filtrate.

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    Model answer

    Blood cells are too big to pass through the walls of the capillaries in the glomerulus. Only small molecules are forced out by the high pressure.

    Mark scheme

    • Too big — 1 mark
    • To pass through the capillary walls — 1 mark
    • Only small molecules are filtered — 1 mark
  4. 4 Explain [3 marks]

    Explain why there is no glucose in the urine of a healthy person.

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    Model answer

    Glucose is filtered into the nephron, because it is a small molecule. All of it is reabsorbed into the blood from the tubule, by active transport, so there is none in the urine.

    Mark scheme

    • Glucose is filtered — 1 mark
    • All of it is reabsorbed — 1 mark
    • By active transport — 1 mark
  5. 5 Calculate [2 marks]

    The concentration of urea in the plasma is 0.03 g per 100 cm³ and in the urine is 1.80 g per 100 cm³. Calculate how many times more concentrated the urea is in the urine.

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    Model answer

    1.80 divided by 0.03 is 60 times.

    Mark scheme

    • 1.80 divided by 0.03 — 1 mark
    • 60 times — 1 mark
  6. 6 Evaluate [6 marks]

    Describe how the kidney forms urine from blood, and explain how the structure of the nephron helps this.

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    Model answer

    Blood flows into the glomerulus, where the pressure is high, because the vessel that leaves is narrower. The high pressure forces small molecules, such as water, glucose, urea and ions, out through the thin walls of the capillaries into Bowman's capsule, but blood cells and proteins are too big, so they stay in the blood. This is filtration, and it is not selective. In the first part of the tubule, all of the glucose is reabsorbed into the blood by active transport, which needs energy, so the cells have many mitochondria. Water is reabsorbed by osmosis, in the loop of Henle and the collecting duct. The urea is not reabsorbed, so it leaves in the urine with the excess water and excess ions.

    Mark scheme

    • High pressure forces small molecules out — 1 mark
    • Cells and proteins stay in the blood — 1 mark
    • All glucose reabsorbed — 1 mark
    • By active transport, using energy — 1 mark
    • Water reabsorbed by osmosis — 1 mark
    • Urea leaves in the urine — 1 mark

Quick check

  1. 1

    Where does filtration take place?

    1. AIn the loop of Henle
    2. BIn the glomerulus and Bowman's capsule
    3. CIn the bladder
    4. DIn the collecting duct
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    B: In the glomerulus and Bowman's capsule

    In the glomerulus and Bowman's capsule.

  2. 2

    Which of these is NOT filtered out of the blood into the capsule?

    1. AWater
    2. BGlucose
    3. CUrea
    4. DBlood cells
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    D: Blood cells

    Blood cells are too large.

  3. 3

    How is glucose reabsorbed?

    1. ABy diffusion
    2. BBy osmosis
    3. CBy active transport
    4. DBy filtration
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    C: By active transport

    By active transport.

  4. 4

    How is water reabsorbed?

    1. ABy osmosis
    2. BBy active transport
    3. CBy filtration
    4. DBy digestion
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    A: By osmosis

    By osmosis.

  5. 5

    What is the liquid in Bowman's capsule?

    1. AThe urine
    2. BThe filtrate
    3. CThe plasma
    4. DThe lymph
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    B: The filtrate

    The filtrate.

  6. 6

    Why does the proximal tubule have many mitochondria?

    1. ATo digest glucose
    2. BTo store urea
    3. CTo make hormones
    4. DTo supply energy for active transport
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    D: To supply energy for active transport

    To supply energy for active transport.

  7. 7

    What is in the urine of a healthy person?

    1. AUrea, excess ions and excess water
    2. BGlucose and proteins
    3. CBlood cells
    4. DAmino acids
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    A: Urea, excess ions and excess water

    Urea, excess ions and excess water.

  8. 8

    Why does the glomerulus have a high pressure?

    1. AIt is next to the heart
    2. BIt contains no water
    3. CThe vessel leaving is narrower than the one entering
    4. DIt is made of muscle
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    C: The vessel leaving is narrower than the one entering

    The vessel that leaves is narrower than the vessel that enters.

  9. 9

    Why is the urea more concentrated in urine than in the plasma?

    1. AUrea is made in the kidney
    2. BWater is reabsorbed but urea is not
    3. CGlucose is added
    4. DUrea is reabsorbed
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    B: Water is reabsorbed but urea is not

    Water is reabsorbed but urea is not.