1. a) Nostril _ nasal cavity _ pharynx _ larynx _ trachea _ bronchi _ bronchioles
b) The lungs are efficient for gaseous exchange because:
• The lungs are made of numerous alveoli which provide a large surface area for gaseous exchange • The surfaces of the alveoli are moist for gases to dissolve
• The alveolar wall is thin consisting of one layer of epithelial cells
• Each alveolus is surrounded by numerous capillary network
c) i) Because they have an anti-sticking chemical called a surfactant covering their surfaces. ii) This chemical acts by reducing the surface tension, hence keeps the alveoli open
2. a) A. Epithelial cell of alveolus B. Thin film of moisture / Alveolar fluid C. Red blood cell D. Endothelial capillary
c) R – Deoxygenate blood S – Oxygenated blood.
d) In the lungs and tissue
e) i) Deoxygenated blood has less oxygen than the alveolar air.
ii) This causes oxygen to diffuse out of the alveolus into the blood capillaries.
f) Oxygen molecules pass through and dissolve in the thin film of moisture in the alveolar wall.
The oxygen then pass through the thin layer of alveolar epithelial cells and the endothelial cells of capillary wall.
g) Oxygenated blood has more oxygen and less carbon dioxide than the tissue.
3. a) A – Water B – Carbonic acid C – Carbonic anhydrase D – Haemoglobinic acid
b) i) Method I: CO2 in the tissue diffuses into the red blood cell.
Method II: CO2 reacts with water to form carbonic acid.
ii) - Catalyses a reaction between carbon dioxide and water to form carbonic acid
- Catalyses the dissociation of carbonic acid into hydrogen carbonate ions and hydrogen ions.
iii) To balance the electrical charge. This is known as the chloride shift.
c) It helps to maintain the blood pH by removing hydrogen ions from solution.
d) - As dissolved carbon dioxide