Gas Exchange in Humans Study Notes

Gas Exchange in Humans: IGCSE Biology Exam Preparation Notes

Exam Overview

• Exam Board: Cambridge International Examinations (CIE)
• Subject: Biology (0610/0970)
• Topic: Gas Exchange in Humans
• Exam Duration: 24 minutes
• Total Marks: 20
• Grading Scale and Boundaries:
    - Grade 9: >85%
    - Grade 8: 75%
    - Grade 7: 68%
    - Grade 6: 60%
    - Grade 5: 53%
    - Grade 4: 48%
    - Grade 3: 40%
    - Grade 2: 33%
    - Grade 1: <25%

Key Questions and Answers

1. Approximate Percentage of Oxygen in Expired Air:
      - Options: A) 0.04% B) 4% C) 16% D) 21%
      - Correct Answer: C) 16%

2. Comparison of Atmospheric Air and Expired Air:
      - Options:
        - A) Less water vapour, less carbon dioxide
        - B) Less water vapour, more carbon dioxide
        - C) More water vapour, less carbon dioxide
        - D) More water vapour, more carbon dioxide
      - Correct Answer: D) More water vapour, more carbon dioxide

3. Path of Carbon Dioxide as it Leaves the Lungs:
      - Options:
        - A) Alveolus → Bronchiole → Bronchus → Trachea
        - B) Alveolus → Bronchus → Bronchiole → Trachea
        - C) Trachea → Bronchiole → Bronchus → Alveolus
        - D) Trachea → Bronchus → Bronchiole → Alveolus
      - Correct Answer: A) Alveolus → Bronchiole → Bronchus → Trachea

4. Gas Exchange in Amphibians Through Skin: Characteristics of Skin Surface:
      - Options:
        - A) Large, thick
        - B) Large, thin
        - C) Small, thick
        - D) Small, thin
      - Correct Answer: B) Large, thin

5. Actions of Intercostal Muscles and Diaphragm During Exhalation:
      - Options:
        - A) Contract, relax, falls
        - B) Contract, relax, rises
        - C) Relax, contract, falls
        - D) Relax, contract, rises
      - Correct Answer: A) Contract, relax, falls

6. Approximate Percentages of Oxygen and Carbon Dioxide in Atmospheric Air:
      - Generally consists of:
        - Approx. 21% Oxygen
        - Approx. 0.04% Carbon Dioxide
        - Remaining composition is Nitrogen (approx. 78%)

7. Pressure and Volume Changes in Lungs:
      - When the external intercostal muscles contract, the volume of air inside the lungs increases, leading to a decrease in pressure.

8. Source of Nitrogen in Expired Air:
      - Options:
        - A) Product of proteins broken down in the mammal
        - B) Product of respiration
        - C) Exchanged for oxygen in the blood
        - D) Present in the air breathed in
      - Correct Answer: D) Present in the air breathed in

9. Factors Helping Oxygen Absorption in Lungs:
      - Options:
        - A) Air breathed in has less oxygen than air breathed out.
        - B) Alveoli have thick walls and a large surface area.
        - C) Alveoli have thin walls and a large surface area.
        - D) Oxygen concentration in blood is higher than in alveoli.
      - Correct Answer: C) Alveoli have thin walls and a large surface area.

10. Lungs Air Pressure Changes Diagram:
        - Atmospheric pressure is approximately 101 kPa. It will be important to analyze the stages of pressure illustrated in the context of breathing cycles.

11. Composition of Air Samples:
        - Questions on differentiating between inspired air and expired air samples based on the concentration of O2, CO2, and N2.

12. Highest Carbon Dioxide Concentration Location:
        - Options:
          - A) To Pulmonary Vein
          - B) From Pulmonary Artery
        - Correct Answer: B) From Pulmonary Artery

13. Further Air Composition Analysis:
        - Continuation on determining the nature of air samples through composition analysis.
    

14. Breathing Analysis of a Girl Holding Her Breath:
        - Options: A) Less carbon dioxide and water vapour; B) Less nitrogen and water vapour; C) Less oxygen and carbon dioxide; D) Less oxygen and nitrogen
        - Correct Answer: A) Less carbon dioxide and water vapour

15. Suitability of Alveoli for Gas Exchange:
        - Factors for alveoli:
          - A) Large total surface area ✓
          - B) Well-supplied with blood vessels ✓
          - Analysis conducted on the components that optimize their role in gas exchange.

16. Graph Analysis of Lung Volume Changes:
        - Changes in lung volumes can be assessed over various time frames, especially post-exercise.

17. Experiment with Expired Air and Atmosphere:
        - Candle experiment to compare oxygen availability in expired air versus atmospheric air.
        - Results show:
          - Gas Jar X (expired air) takes longer to extinguish.
          - Gas Jar Y (atmospheric air) extinguishes quicker.
          - Explanation: Jar X contains expired air which has more carbon dioxide, affecting oxygen levels.

18. Carbon Dioxide Movement Between Alveolus and Capillary:
        - Reason: Carbon dioxide moves from the higher concentration in blood to a lower concentration in air (alveolus) to maintain gas exchange efficiency.

19. Function of Ciliated Cells:
        - The functions of ciliated epithelial cells include:
          - Moving mucus towards the throat
          - Important for protecting the airway by trapping dust and pathogens.

20. Function of Parts Labelling in Ciliated Cells (X):
        - Explained as a critical mechanism in moving mucus and trapping particles, showcasing the respiratory system's role in homeostasis.