organisation

• Circulatory system

  Transport system that distributes essential molecules efficiently in organisms beyond a certain size
• Organism

  e.g. very early embryo
• Transport system


  • Made up of tubes or 'vessels' that carry materials from one part of the organism to another
  • Makes close contact with cells, such as those of exchange surfaces
• Substances transported in the blood

  • Oxygen
  • Carbon dioxide
  • Glucose
  • Urea
  • Antibodies
  • Hormones
• Oxygen


  Carried in red blood cells
• Dissolved substances

  Carried in the plasma
• oxygen is transported from the lungs to all of the body's cells
• carbon dioxide is transported from all of the body's cells back to the lungs
• glucose is transported from the digestive system to the liver and then all of the body's cells
• urea is transported from the liver cells to the kidneys
• antibodies are transported around the whole body
• hormones are transported in the bloodstream and are carried to target organs
• Surfaces and body organs in multicellular organisms

  • Specialised for exchanging materials
• Effectiveness of exchange surfaces in plants and animals

  • Increased by having a large surface area
  • Increased by having a short distance required for diffusion
• Large surface area

  • Flattened shape of structures such as leaves
  • Alveoli in the respiratory system
  • Villi in the digestive system
• Short distance required for diffusion

  • Membranes of cells
  • Flattened shape of structures such as leaves
  • Walls of blood capillaries are one cell thick
  • Epithelia of alveoli in the respiratory system and the villi in the small intestine are only one cell thick
• Large, flat leaves like this green taro leaf


  • Have an effective exchange surface
• Additional adaptations for effective exchange surfaces in animals

  • Efficient blood supply to transport molecules to and from the exchange surface
• Efficient blood supply

  • Network of blood capillaries that surrounds each alveolus in the lungs
  • Network of blood capillaries in each villus in the small intestine
• Ventilation


  The process of breathing that brings air to, and removes air from the exchange surface - the alveoli
• Concentration gradient

  The steep gradient maintained by the moving blood and ventilated surfaces, which increases effective exchange
• Carbohydrates

  • Source of energy
  • Glucose is the main respiratory substrate
• Major sources of carbohydrates

  • Starch: potatoes, rice and wheat products, bread, cereals and pasta
  • Sugars: fruit, smoothies, fizzy drinks, chocolate and sweets