efficient transport and exchange

• As organisms become bigger, the surface area to volume ratio is smaller.
• Transport of substances:

  • Oxygen in alveoli — respiration

  • Carbon dioxide in alveoli — waste product of metabolism

  • Water in kidney nephrons — cell function

  • Dissolved food molecules in small intestine — respiration

  • Mineral ions in small intestines — cell function

  • Urea in kidney nephrons — waste product of metabolism
• Alveoli have a large surface area and thin cell walls.
• SA/V determines efficiency of exchange surfaces.
• The larger the SA/V, the more efficient the exchange surface.