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• What is the primary function of the circulatory system?

  To transport essential molecules throughout the body
• How do single-celled organisms transport essential molecules?

  By diffusion
• What happens when an organism exceeds a certain size?

  It requires a transport system for efficient distribution of essential molecules
• What is the maximum distance for efficient diffusion in cells?

  100 µm
• Why is diffusion inefficient over long distances?

  Because the diffusion path becomes too large
• What are the common features of transport systems?

  They consist of tubes or vessels that carry materials
• What substances are transported in the blood?

  • Oxygen: from the lungs to all body cells
  • Carbon dioxide: from all body cells to the lungs
  • Glucose: from the digestive system to the liver, then to all body cells
  • Urea: from liver cells to the kidneys
  • Other substances: antibodies and hormones
• What is the role of the heart in the circulatory system?

  To pump blood around the body
• How many chambers does the heart have?

  Four chambers
• What are the names of the heart's chambers?

  Two atria and two ventricles
• How does blood enter the heart?

  Through the atria
• What prevents blood from flowing back into the atria?

  Heart valves
• What is the main artery blood leaves the heart through?

  The aorta
• What are the two circuits of the human circulatory system?

  1. Pulmonary circulation: transports blood to the lungs
  2. Systemic circulation: transports blood to the body
• What occurs in the pulmonary circulation?

  Oxygen diffuses into the blood and carbon dioxide diffuses out
• What does the systemic circulation transport?

  Oxygen and nutrients to the body, and carbon dioxide and wastes away from cells
• Why is systemic circulation under high pressure?

  To deliver blood to the extremities of the body
• Why is pulmonary circulation under lower pressure?

  Because blood is delivered only to the lungs, which are close to the heart
• What happens to blood during one complete circulation of the body?

  • Deoxygenated blood enters the right atrium from the body
  • Blood passes through the tricuspid valve to the right ventricle
  • Blood is pumped to the lungs for oxygenation
  • Oxygenated blood returns to the left atrium
  • Blood is pumped from the left ventricle to the aorta and distributed to the body