Ad Banner Placeholder

Cambridge IGCSE Biology · 0610

Chapter 9: Transport in animals (Part 1)

Circulatory systems

The circulatory system is the main transport system in animals, comprising a pump (the heart), blood vessels, and valves to ensure one-way flow.

Single circulatory system (fish)
Blood passes through the heart only once for each complete circuit of the body. The heart has only two chambers, and oxygen is absorbed as blood passes the gills.
Double circulatory system (mammals)
Blood passes through the heart twice for each complete circuit of the body.
  • Advantages: It is more efficient at supplying oxygen and can maintain a high blood pressure.
  • Need: Mammals are larger and require more oxygen for respiration for warmth (compared to cold-blooded fish).

Structure of the mammalian heart

The mammalian heart has four chambers to keep oxygenated and deoxygenated blood separate:

Muscular walls
The walls of both ventricles are thicker than the atria walls.
Septum
A wall that separates the left and right sides to ensure oxygenated and deoxygenated blood remain separate.
Atria
The upper chambers (left and right) that receive blood.
Ventricles
The lower chambers (left and right) that pump blood out. The left ventricle wall is much thicker than the right side because it must pump blood at high pressure around the entire body, whereas the right side only pumps to the lungs.
Coronary arteries
Supply the heart muscle itself with oxygenated blood.
Valves
Prevent backflow of blood.
  • Atrioventricular valves: Include the tricuspid (right side) and bicuspid (left side) valves between the atria and ventricles.
  • Semilunar valves: Located at the exits of the heart into the arteries.
Internal structure of the human heart showing four chambers, septum, left ventricle wall, and main blood vessels with blood flow arrows
Diagram 1: Internal structure of the human heart. The four chambers, septum, thick muscular wall of the left ventricle, and the four main blood vessels (vena cava, pulmonary artery, pulmonary vein, and aorta) are labelled. Arrows show the direction of blood flow through the heart.

Exam Traps

  • Do not say the right ventricle pumps to the body — it pumps to the lungs only.

Functioning of the heart

Blood moves through the heart in a specific sequence:

  1. Deoxygenated blood enters the right atrium via the vena cava.
  2. The atrium contracts, pushing blood through the tricuspid valve into the right ventricle.
  3. The ventricle contracts, pushing blood past the semilunar valve into the pulmonary artery toward the lungs.
  4. Oxygenated blood returns from the lungs via the pulmonary vein into the left atrium.
  5. The atrium contracts, pushing blood through the bicuspid valve into the left ventricle.
  6. The ventricle contracts, pushing blood past the semilunar valve into the aorta to travel around the body.

Exam Traps

  • Do not assume all arteries carry oxygenated blood — the pulmonary artery carries deoxygenated blood.
  • Avoid reversing pulmonary artery and pulmonary vein or placing the aorta on the right side of the heart.

Monitoring heart activity

The activity of the heart can be monitored by:

  • Electrocardiogram (ECG): Records electrical signals causing contractions.
  • Pulse rate: Measuring the number of heartbeats per minute.
  • Sound: Listening to the sounds of valves closing.

Effect of physical activity

During physical activity, the heart rate increases. Muscles respire to produce energy for movement, which requires more oxygen. The heart speeds up to pump blood more quickly, delivering more oxygen to respiring tissues.

0/15

Ad Banner Placeholder