IMO Practice Test — Breathing and Exchange of Gases
6 Questions • 15 min • Olympiad level
15:00
Question 1 of 6
Oxygen diffuses from the alveoli into the blood because in the alveoli the oxygen level is:
Higher than in the incoming blood
Lower than in the blood
Equal to the blood
Zero
Explanation: Diffusion runs from high to low; alveolar O₂ is higher than in the venous blood, so O₂ moves into the blood.
Question 2 of 6
Haemoglobin is well suited to its job because it picks up oxygen where O₂ is ____ and releases it where O₂ is ____.
High; low
Low; high
Zero; zero
Equal; equal
Explanation: It loads O₂ in the high-oxygen lungs and unloads it in the low-oxygen tissues.
Question 3 of 6
Carbon-monoxide poisoning is dangerous mainly because CO:
Binds haemoglobin more strongly than oxygen does
Adds oxygen to blood
Speeds breathing safely
Has no effect
Explanation: CO binds haemoglobin far more tightly than O₂, blocking oxygen transport.
Question 4 of 6
Emphysema reduces gas exchange chiefly because the breakdown of alveolar walls:
Decreases the surface area for diffusion
Increases haemoglobin
Makes the trachea wider
Adds more alveoli
Explanation: Fewer, larger air spaces mean less surface area, so less oxygen can be absorbed.
Question 5 of 6
Breathing rate increases during exercise mainly to:
Supply more oxygen and remove more CO₂
Cool the blood only
Make more haemoglobin
Reduce oxygen need
Explanation: Active muscles need more O₂ and produce more CO₂, so ventilation rises.
Question 6 of 6
A worker constantly exposed to fine stone dust without a mask is at risk of:
Silicosis
Jaundice
Anaemia
Tooth decay
Explanation: Inhaled silica dust scars the lungs, causing silicosis — an occupational disease.