Science HEALTH

• Surface Area to Volume Ratio (SA/Vol)

  Higher SA/Vol facilitates efficient exchange of gases
• Rate of Diffusion

  The rate at which gases move across membranes, influenced by concentration gradients and SA/Vol
• Organs involved in Gaseous Exchange


  • Lungs (alveoli)
  • Trachea
  • Bronchi
  • Bronchioles
• Changes in Chest Cavity for Breathing


  1. Inspiration: Diaphragm contracts, ribs lift -> increase in thoracic volume -> air drawn in

  2. Expiration: Diaphragm relaxes, ribs lower -> decrease in thoracic volume -> air expelled
• Inspiration


  Decreased pressure in lungs compared to atmospheric pressure
• Expiration


  Increased pressure in lungs compared to atmospheric pressure
• Mucus


  Traps pathogens/particles
• Cilia


  Move mucus upward
• Blood Composition

  • Plasma: 55%
  • Red blood cells: 45%
  • White blood cells and Platelets: 1%
• Plasma

  Transports nutrients and hormones, removes waste, maintaining blood pressure
• Red Blood Cells (RBCs)

  • Biconcave, no nucleus, filled with haemoglobin for oxygen transport
• White Blood Cells (WBCs)

  Part of the immune system, defend against pathogens
• Platelets

  Assist in blood clotting
• Alveolar Structure


  • Single-cell thick walls, large surface area for efficient exchange
  • Thin walls increase efficiency of gas exchange
• Factors Affecting Rate of Diffusion


  Increased concentration gradient enhances diffusion rate
• Process of Gaseous Exchange

  Oxygen diffuses from alveoli into blood, carbon dioxide from blood into alveoli
• Cardiac muscle

  Pumps blood around body
• Blood Circulation and Heart Function

  Synchronized pumping, blood flow controlled by valves
• Cellular Respiration


  Nutrients + oxygen -> energy + carbon dioxide + water
• Mitochondria


  Site of cellular respiration in cells
• Position of Arteries, Veins, and Capillaries

  • Arteries: Carry blood away from heart, oxygenated (except pulmonary)
  • Veins: Carry blood toward heart, deoxygenated (except pulmonary)
  • Capillaries: Allow exchange between blood and tissues
• Tissue Fluid

  Formed by exchange between blood and tissues via capillary walls
• Lymph Vessels

  Take up excess tissue fluid
• Oxygenated and Deoxygenated Blood


  • Oxygenated: Blood leaving heart (except pulmonary artery)
  • Deoxygenated: Blood returning to heart (except pulmonary vein)