Read the following passage and answer the questions that follow.
Amit's grandfather was admitted to hospital with complaints of breathlessness and fatigue. The doctor found that the alveolar walls had thickened and some alveoli were damaged, reducing the surface area available for gas exchange. The doctor also noted that his haemoglobin levels were significantly low (anaemia). The doctor explained that both conditions together were seriously reducing oxygen delivery to body tissues.
(i) How does thickening and damage of alveolar walls reduce the efficiency of gas exchange in the lungs? (1 mark)
(ii) Name the pigment that normally carries oxygen in human blood and state where it is located in the blood. (1 mark)
(iii) Carbon dioxide is transported differently from oxygen in human blood. Explain how carbon dioxide is mainly transported. (1 mark)
(iv) Even if the alveoli were healthy, explain why a very low haemoglobin level would still cause oxygen deficiency in body tissues. (1 mark)
Generated by claude-sonnet-4-6 · 2026-06-26 01:00 · grounding rag
Model Answer
(i) Thickening of alveolar walls increases the distance over which gases must diffuse, slowing down diffusion. Damage reduces the total surface area available for gas exchange, so less oxygen can enter the blood per breath, causing breathlessness.
(ii) The pigment is haemoglobin. It is located in the red blood corpuscles (RBCs).
(iii) Carbon dioxide is mainly transported in dissolved form in the plasma of blood. Unlike oxygen, it does not require a carrier pigment and is carried as dissolved CO₂ from body tissues to the lungs for removal.
(iv) Even with healthy alveoli, oxygen that diffuses into blood cannot be carried to tissues if haemoglobin is very low. Since oxygen is transported by RBCs (haemoglobin), insufficient haemoglobin means very little oxygen reaches body tissues, causing oxygen deficiency.
Source: Chapter 5, Section 5.4 Transportation in Human Beings
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Explanation
- (i) Examiners expect mention of two effects: increased diffusion distance (thickening) + reduced surface area (damage).
- (ii) Both parts are needed for 1 mark — name the pigment AND its location.
- (iii) The textbook states plasma transports CO₂ in dissolved form. Avoid saying CO₂ is carried by haemoglobin (that is oxygen's role).
- (iv) The key logic: alveoli = site of exchange; haemoglobin = transport vehicle. Healthy lungs can't help if the carrier molecule is absent. This is directly linked to Exercise Q10 in the chapter.