2.7 biology

• Lungs


  Organs responsible for gas exchange
• Alveoli


  • Tiny sacs in lungs that form the gas exchange surface
  • They have a large surface area, thin walls and an extensive blood supply
• Gas exchange


  The movement of molecules such as oxygen and carbon dioxide
• Digestion


  The breakdown of large, insoluble food molecules into smaller, soluble ones
• Small intestine


  Organ in the digestive system that contains many microscopic villi
• Villi


  • Finger-like projections of the small intestine lining for the digestion of food
  • They have a large surface area, thin walls and an extensive blood supply
• Blood capillaries


  Absorb glucose and amino acids in the villi
• Lacteal


  Absorb fatty acids and glycerol in the villi
• Why does blood need to carry oxygen & nutrients?

  • Oxygen and nutrients from food must be absorbed into the bloodstream to be delivered to cells for respiration
  • Waste materials, such as carbon dioxide, must be removed from cells into the bloodstream
• Features of surfaces involved in the absorption of materials

  • Large surface area
  • Thin walls
  • Extensive blood supply