Marking Scheme: Excretion

This is the marking scheme for quiz: Excretion Quiz
Study guide: Excretion

Short Answer Questions

1. State the name of the gas excreted through the lungs and write the balanced chemical equation for its production during cellular respiration.

Marks: 2

  • Gas name: carbon dioxide, CO₂ (1 mark)
  • Balanced chemical equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (1 mark)

2. What are the two main regions of the kidney? Describe their functions.

Marks: 3

  • Cortex: Outer region, contains nephrons, tubules, and collecting ducts. (1 mark)
  • Medulla: Inner region, contains collecting ducts, renal pelvis, and ureter. (1 mark)

3. Explain how urea is produced in the human body. Include a chemical equation.

Marks: 2

  • Urea is produced in the liver from excess amino acids. (1 mark)
  • Chemical equation: R-COOH + NH₃ + CO₂ → CO₂ + H₂O + urea (NH₂CONH₂) or equivalent (1 mark)

4. Describe the process of deamination. How does it relate to urea formation?

Marks: 2

  • Deamination removes amino groups from amino acids. (1 mark)
  • Ammonia is released during deamination and combines with carbon dioxide to form urea. (1 mark)

5. Outline the steps involved in urine formation within a nephron.

Marks: 4

  • Filtration: Blood pressure forces water, glucose, salts, and urea into Bowman capsule, forming filtrate. (1 mark)
  • Reabsorption: Proximal tubule reabsorbs glucose, salts, and water. (1 mark)
  • Loop of Henle: Concentrates filtrate by reabsorbing water and chloride ions. (1 mark)
  • Urine formation: Remaining filtrate becomes urine, containing urea, excess water, and ions. (1 mark)

6. State the three substances excreted by the kidneys. Explain why each is important to be excreted.

Marks: 4

  • Substances excreted:

    • Urea (1 mark)
    • Excess water (1 mark)
    • Ions (e.g., sodium, potassium) (1 mark)

  • Reasons for excretion:

    • Urea is toxic when in high concentrations. (1 mark)
    • Excess water causes dehydration or kidney damage. (1 mark)
    • Ion levels must be controlled for muscle function and nerve transmission. (1 mark)

7. What happens if waste products like urea are not excreted? Give reasons for each consequence.

Marks: 2

  • Consequences:
    • Brain damage (1 mark)
    • Heart failure (1 mark)
    • Liver damage (1 mark)
    • Confusion and coma (1 mark)

8. Describe the structure of the nephron, including the glomerulus and tubules. Explain their functions.

Marks: 4

  • Nephron structure:

    • Glomerulus: cluster of capillary loops surrounded by Bowman capsule (1 mark)
    • Proximal tubule: tube after Bowman capsule (1 mark)
    • Loop of Henle: descends and ascends in medulla (1 mark)
    • Distal tubule: further reabsorption (1 mark)
    • Collecting duct (1 mark)

  • Functions:

    • Glomerulus filters blood into filtrate (1 mark)
    • Tubules reabsorb useful materials (1 mark)
    • Collecting duct receives final urine (1 mark)

9. Which of the following statements about urea is correct?

Marks: 1

  • Correct answer: B) Urea is produced in the liver from excess amino acids. (1 mark)

  • Distractors:

    • A) Incorrect: Urea is produced in the liver, not kidneys. (0 marks)
    • C) Incorrect: Urea production is not limited to exercise. (0 marks)
    • D) Incorrect: Urea is waste, not a nutrient. (0 marks)

10. Which kidney region is primarily responsible for producing concentrated urine?

Marks: 1

  • Correct answer: B) Medulla (1 mark)

  • Distractors:

    • A) Incorrect: Cortex is the outer region. (0 marks)
    • C) Incorrect: Both regions contribute, but medulla produces concentrated urine. (0 marks)
    • D) Incorrect: Neither is correct. (0 marks)

Total Marks: 20