Exchanging Materials

• What is the surface area to volume ratio of single-celled organisms?

  Relatively large
• Why do single-celled organisms have a large surface area to volume ratio?

  To facilitate necessary exchanges with the environment
• How are organs in multicellular organisms adapted for exchange?

  They are specialised with effective exchange surfaces
• What features do exchange surfaces usually have?

  Large surface area and thin walls
• Why is a short diffusion distance important for exchange surfaces?

  It allows for efficient material exchange
• What is necessary for efficient gaseous exchange in animals?

  Efficient blood supply or ventilation
• What are the key features of efficient exchange surfaces?

  • Large surface area
  • Thin membranes or short diffusion path
  • Efficient transport system (e.g., blood supply)
• What is the role of alveoli in the lungs?

  To absorb oxygen during breathing
• How do alveoli maintain a concentration gradient for oxygen absorption?

  By having a good blood supply to carry oxygen away
• What is the function of villi in the small intestine?

  To absorb soluble food molecules
• What adaptations do fish have for gaseous exchange?

  Gills that exchange gases between water and blood
• Why do large organisms need specialised exchange surfaces?

  To obtain food and oxygen efficiently
• How do plant roots increase their surface area for water absorption?

  By having long, thin roots and root hair cells
• What adaptations do plant leaves have for efficient gaseous exchange?

  They are flat and thin with internal air spaces and stomata
• What happens to the surface area to volume ratio as organisms increase in size?

  It decreases
• What is the SA:V ratio of a 1cm cube?


  6:1
• What is the SA:V ratio of a 3cm cube?


  2:1