The Circulatory System (ICSE Class 10): 29 MCQs with answers

Heart, blood vessels, and blood

The circulatory system is made of a pump (heart), tubes (blood vessels), and a fluid (blood). The lungs are part of the respiratory system, not the circulatory system itself.

separates oxygenated and deoxygenated blood

The septum is the muscular wall dividing the right and left sides of the heart, keeping oxygenated and deoxygenated blood from mixing.

Vena cava

Deoxygenated blood returns from the body to the right atrium through the vena cava.

Left ventricle

The left ventricle pumps blood to the entire body, so it must work against greater distance and resistance, giving it the thickest wall.

Tricuspid valve

The tricuspid valve guards the opening between the right atrium and right ventricle. The bicuspid (mitral) valve is on the left side.

White blood cells

White blood cells (WBCs) defend the body against pathogens. RBCs transport oxygen, platelets help clotting, and plasma carries dissolved substances.

True

The pulmonary artery is the only artery that carries deoxygenated blood, and the pulmonary vein is the only vein that carries oxygenated blood.

To pump blood

The heart's primary function is to pump blood throughout the body, ensuring the transport of oxygen, nutrients, and waste.

Four chambers

The heart is structured with four chambers: two atria and two ventricles, allowing for efficient blood circulation.

Deoxygenated blood

Veins typically carry deoxygenated blood back to the heart, except for the pulmonary vein, which carries oxygenated blood.

To prevent blood from flowing backwards

Valves in the heart and veins prevent the backflow of blood, ensuring it flows in one direction.

To exchange materials between blood and tissues

Capillaries are where the exchange of oxygen, nutrients, and waste occurs between blood and tissues due to their thin walls.

Right atrium

The right atrium receives deoxygenated blood from the body via the vena cava.

Red blood cells

Red blood cells contain hemoglobin, which binds to oxygen and transports it throughout the body.

To separate oxygenated and deoxygenated blood

The septum separates the right and left sides of the heart, preventing the mixing of oxygenated and deoxygenated blood.

Pacemaker (SA node)

The pacemaker, or SA node, in the right atrium regulates the heartbeat rhythm automatically.

Lungs

Gas exchange occurs in the lungs, where oxygen is absorbed into the blood and carbon dioxide is released.

Arteries carry blood away from the heart

Arteries carry blood away from the heart and veins carry it towards the heart. The direction, not oxygen content, defines them.

carries deoxygenated blood to the lungs

The pulmonary artery is the only artery that carries deoxygenated blood — it takes it from the right ventricle to the lungs for oxygenation.

Because the pulmonary artery carries deoxygenated blood

The rule about arteries is about direction (away from the heart), not oxygen content. The pulmonary artery is the exception — it carries deoxygenated blood.

Pulmonary vein → left atrium → left ventricle → aorta

Oxygenated blood returns via the pulmonary vein to the left atrium, passes into the left ventricle, and is pumped into the aorta.

To allow fast diffusion of gases and nutrients

Capillaries are the site of exchange between blood and tissues. A one-cell-thick wall makes diffusion of oxygen, nutrients, and waste fast and efficient.

Systole

Systole is the contraction phase when ventricles push blood out. Diastole is the relaxation phase when they refill.

It sets the heartbeat rhythm

The SA node, located in the right atrium, acts as the pacemaker and sets the rhythm of the heartbeat automatically.

keeps oxygenated and deoxygenated blood separate

In double circulation, blood passes through the heart twice per circuit. This separation of oxygenated and deoxygenated blood ensures a high, steady oxygen supply — essential for warm-blooded animals.

Coronary artery

Coronary arteries supply blood to the heart muscle itself. A block starves the heart muscle of oxygen, causing a heart attack.

Decreased blood flow to the systemic circulation

The left ventricle pumps oxygenated blood into the systemic circulation. A blockage here would decrease blood flow to the body, leading to insufficient oxygen and nutrient delivery.

8400 mL/min

Cardiac output is calculated using the formula: Cardiac Output = Heart Rate × Stroke Volume. Thus, $120 ext{ beats/min} imes 70 ext{ mL/beat} = 8400 ext{ mL/min}$.

Hypertrophy of the left ventricular wall

Prolonged high blood pressure causes the heart muscle, especially the left ventricle, to thicken (hypertrophy) as it works harder to pump against increased resistance.