MDCAT Biology chapter 11: Biology · Circulation MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
48 exam-style questions on Biology · Circulation, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. The largest white blood cells, which leave the blood and become macrophages in the tissues, are the
A
neutrophils
B
lymphocytes
C
monocytes
D
basophils
Show answer
Answer: C. Monocytes are the largest leucocytes, with a kidney-shaped nucleus; in the tissues they become macrophages that engulf microbes and debris. Neutrophils are the most numerous phagocytes but are smaller.
2. A blood clot forms in a deep vein of the leg, breaks loose, travels in the blood and blocks a branch of the pulmonary artery. The travelling clot is called
A
a thrombus
B
an atheroma
C
an aneurysm
D
an embolus
Show answer
Answer: D. A clot that stays where it formed is a thrombus; once it breaks free and travels in the blood it is an embolus, and the blockage it causes is an embolism. An atheroma is a fatty plaque.
3. Which vessel attached to the heart carries deoxygenated blood away from the heart?
A
aorta
B
pulmonary vein
C
superior vena cava
D
pulmonary artery
Show answer
Answer: D. The pulmonary artery takes deoxygenated blood from the right ventricle to the lungs. The superior vena cava also carries deoxygenated blood, but towards the heart, and the pulmonary veins bring oxygenated blood back.
4. Stimulation of the vagus (parasympathetic) nerve to the heart
A
speeds up the heart by acting on the SA node
B
stops the atria but not the ventricles
C
slows the heart by acting on the SA node
D
makes the ventricles beat before the atria
Show answer
Answer: C. Vagus nerve impulses slow the pacemaker and so reduce the heart rate; sympathetic nerves and adrenaline speed it up. The cardiac centre in the medulla oblongata controls both.
5. While blood is being pumped out of the ventricles into the aorta and pulmonary trunk, the heart valves are in which state?
A
semilunar valves open; tricuspid and bicuspid valves closed
B
semilunar valves closed; tricuspid and bicuspid valves open
C
all four valves open
D
all four valves closed
Show answer
Answer: A. Ventricular pressure is then above arterial pressure, so the semilunar valves are pushed open, while the same high pressure keeps the atrioventricular valves shut and stops backflow into the atria.
6. A stroke is the death of part of the brain. It happens when
A
an artery supplying that part of the brain is blocked or bursts
B
a coronary artery is blocked, so part of the heart muscle dies
C
a clot forms in a deep vein of the leg and stays where it formed
D
its neurons slowly degenerate with age while the blood supply is normal
Show answer
Answer: A. Brain cells die within minutes without oxygen, so a thrombus or embolus blocking a cerebral artery, or a weakened artery that bursts (cerebral haemorrhage), kills the tissue it supplies. A blocked coronary artery causes a heart attack, not a stroke.
7. A heart attack (myocardial infarction) happens when
A
a coronary artery is blocked and part of the heart muscle dies
B
a heart valve becomes leaky so that blood flows backwards
C
an artery in the brain bursts or is blocked by a clot
D
the SA node fires too quickly for the ventricles to fill properly
Show answer
Answer: A. Blockage of a coronary artery, usually by a clot on an atherosclerotic plaque, cuts off the oxygen supply to part of the heart muscle, which dies (infarction). A burst or blocked artery in the brain causes a stroke.
8. Platelets (thrombocytes) are
A
small nucleated cells made in the lymph nodes to start clotting
B
red blood cells that have lost their haemoglobin
C
fragments of large bone marrow cells, involved in clotting
D
young white cells that will later become lymphocytes
Show answer
Answer: C. Platelets are cell fragments pinched off from large cells (megakaryocytes) in the red bone marrow; they have no nucleus and release substances that start blood clotting.
9. A heart removed for transplant goes on beating for a while if it is supplied with warm oxygenated fluid, even though all its nerves have been cut. This shows that the heartbeat
A
is neurogenic, started by impulses from the vagus nerve
B
is myogenic, starting in the SA node of the atrial wall
C
depends on adrenaline released from the adrenal glands
D
is set off by the stretching of the aorta by blood
Show answer
Answer: B. Cardiac muscle is myogenic: each beat begins at the SA node in the wall of the right atrium. Nerves and hormones only speed up or slow down the rate set by the SA node.
10. In elephantiasis, parasitic filarial worms block the lymph vessels of the legs. The legs swell enormously because
A
the worms burst the leg arteries, so blood leaks out into the tissues
B
tissue fluid can no longer drain away and builds up in the tissues
C
blood clots form in the leg veins and stop all venous return
D
the worms multiply until they fill the muscles of the legs
Show answer
Answer: B. Excess tissue fluid normally drains away as lymph. When the lymph vessels are blocked, the fluid accumulates in the tissues and the limb swells (lymphatic oedema).
48, each with the answer and a short explanation, across 3 topics: The heart, Blood and blood vessels, Lymphatic system and disorders. Every chapter test draws ten of them, so you can take it many times.
Is the MDCAT Biology chapter 11 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
