IMO Practice Test — Body Fluids and Circulation
6 Questions • 15 min • Olympiad level
15:00
Question 1 of 6
The left ventricle has the thickest wall because it must:
Pump blood to the whole body
Receive blood from the lungs
Store blood
Make blood cells
Explanation: Pumping blood all around the body needs the greatest force, so its wall is thickest.
Question 2 of 6
Double circulation is efficient because it keeps:
Oxygen-rich and oxygen-poor blood separate
All blood the same
The heart from beating
Lungs from working
Explanation: Separating oxygenated and de-oxygenated blood ensures tissues get fully oxygen-rich blood.
Question 3 of 6
Veins have valves but most arteries do not because:
Vein blood flows slowly at low pressure and could flow backward
Veins carry no blood
Arteries are thinner
Arteries are colourless
Explanation: Low-pressure venous return needs valves to stop backflow; high-pressure arterial flow does not.
Question 4 of 6
Before a blood transfusion, blood groups must be matched to avoid:
Clumping (agglutination) of red cells
Faster digestion
More oxygen
Higher immunity
Explanation: Mismatched groups cause the recipient's antibodies to clump the donor cells — a dangerous reaction.
Question 5 of 6
Atherosclerosis raises the risk of a heart attack because narrowed arteries:
Reduce blood flow to the heart muscle
Increase oxygen to the heart
Make more platelets
Widen over time
Explanation: Fatty deposits choke the heart's blood supply, so a blockage can starve the muscle of oxygen.
Question 6 of 6
The 'lub-dub' heart sounds are produced by:
The closing of heart valves
Blood entering the lungs
Breathing
Digestion
Explanation: The two sounds come from the heart valves snapping shut during the cardiac cycle.