The heart and blood vessels: The heart is an organ that pumps blood around the body in a double circulatory system. The right ventricle pumps blood to the lungs where gas exchange takes place. The left ventricle pumps blood around the rest of the body.

The idea

The heart is a muscular organ that acts as a double pump, keeping oxygenated and deoxygenated blood separate. In the double circulatory system, blood passes through the heart twice per complete circuit. The right ventricle receives deoxygenated blood from the right atrium and contracts to pump it through the pulmonary artery to the lungs, where gas exchange loads oxygen and removes carbon dioxide. Oxygenated blood returns via the pulmonary vein to the left atrium, then enters the left ventricle. The left ventricle has a thicker muscular wall because it pumps blood at higher pressure around the whole body via the aorta, whereas the right ventricle pumps only to the lungs. Valves prevent backflow, so blood travels in one direction.

What earns the marks

• States that the heart is an organ and a muscular pump that maintains circulation of blood around the body.
• Explains that the double circulatory system means blood passes through the heart twice for each complete circuit of the body.
• Describes the right ventricle pumping deoxygenated blood to the lungs, where gas exchange takes place.
• Describes the left ventricle pumping oxygenated blood around the rest of the body.
• Links the thicker muscular wall of the left ventricle to the greater distance and higher pressure needed to pump blood around the body.
• Recognises that the right and left sides of the heart are separated so oxygenated and deoxygenated blood do not mix.

Common mistakes and how to put them right

• Saying the right ventricle pumps blood to the body and the left ventricle pumps to the lungs.

  Put it right by linking right to lungs and left to body.

• Writing that blood passes through the heart once per circuit.

  Put it right by stating that in a double circulatory system it passes through twice.

• Claiming the left ventricle wall is thicker because it holds more blood.

  Put it right by explaining it generates higher pressure to pump blood around the whole body.

Exam tips

• Use the words right and left from the point of view of the person whose heart it is, not the viewer looking at a diagram.
• When asked to explain, always link the chamber to its destination and the function of that destination, such as lungs for gas exchange.
• Compare the two ventricles explicitly: thicker wall, higher pressure, longer distance for the left ventricle.