exchange surfaces

• factors affecting the movement of substances

  1. surface area to volume ratio
  2. temperature
  3. concentration gradient [the greater difference between the inside and the outside of the cell, the faster the rate]
• unicellular organisms


  substances can diffuse in and out of cells quickly across the cell membrane. diffusion is quick because:

  • substances only have to travel a short distance.
  • unicellular organisms have a relatively large surface area to volume ratio
• multicellular organisms


  diffusion is slower because:

  • some cells are deep inside the organism
  • larger organisms have a lower surface area to volume ratio
• gas exchange - lungs

  • the job of the lungs is to transfer oxygen to the blood and remove waste carbon dioxide from it.
  • lungs have alveoli
• alveoli


  • specialised to maximise oxygen and carbon dioxide diffusion
  • large surface area
  • very thin walls
  • moist lining for dissolving gases
  • good blood supply
• villi


  the small intestine is where dissolved food molecules are absorbed out of the digestive system and into the blood.

  the inside of the small intestine is covered in million and millions of villi.

  • villi increase the surface area to volume ratio
  • villi have a single layer of surface cells
  • a very good blood supply to assist quick absorption.
• leaves


  leaves are specialised to maximise the diffusion of oxygen and carbon dioxide.

  • they are broad = large surface area
  • thin, meaning gases only have to travel a short distance.
  • air spaces = lets gases move easily between cells, increasing surface area for gas exchange.
  • stomata
• root hair cells


  each branch of the root is covered in millions of these microscopic hairs

  • large surface area for absorbing mineral ions and water
  • mineral ions move in by active transport
  • water moves in by osmosis