Exchange surfaces

• smaller organisms

  larger SA:V ratio

  decrease diffusion distance

  cells are within a close distance to the environment so simple diffusion can occur
• adaptation points to use

  1. surface area
  2. concentration gradient
  3. diffusion pathway length
• trachea adaptation

  c-shaped rings of cartilage -> prevents collapse

  ciliated epithelial tissue and goblet cells

  smooth muscle and elastic tissue -> allow lumen to stretch and recoil to restrict air flow
• alveoli adaptations

  large surface area -> millions of alveoli

  short diffusion distance -> 1 cell thick wall

  made up of squamous epithelial cells

  network of capillaries maintain a concentration gradient
• inspiration

  • thorax volume increases
  • reduces pressure inside the lungs below atmospheric pressure
  • diaphragm contracts
  • ribcage moves up and outwards
  • internal intercostal muscles relax
  • external intercostal muscles contract
• vital capacity

  maximum air an individual can inhale and exhale during one deep breath at rest
• tidal volume

  volume of air inhaled and exhaled at rest
• residual volume

  volume of air that remains in the lungs to prevent them from collapsing
• oxygen consumption equation


  gradient
• ventilation rate 


  tidal volume x breathing rate
• fish ventilation

  • mouth opens
  • buccal cavity lowers
  • volume increases and pressure decreases
  • operculum valve is shut as the operculum cavity opens
  • floor of the buccal cavity is raised and mouth closes
  • this causes pressure inside the BC increases
  • which forces water out the gills
• layers of the gills

  made up of gill filaments

  increases surface area

  covered in gill lamellae which have very thin membranes

  network of capillaries -> short diffusion distance
• counter-current flow


  water flows in the opposite direction to the flow of blood in the capillaries which ensures that there is always a steep concentration gradient the entirety of the gill lamellae so that the maximum amount of oxygen is absorbed
• adaptations of the tracheal system in insects

  • short diffusion distance -> tracheae branch into tracheoles
  • large surface area -> lots of tracheoles
  • concentration gradient -> close distance to respiring cells
• tracheal system in insects

  anaerobically respire

  produce lactate

  lowers the water potential of the cells causing tracheal fluid to move in via osmosis

  decreases the volume of tracheal fluid in the tracheae and tracheoles which decreases pressure causing air to move in
• spirometers


  Co2 is absorbed by soda lime to reduce respiratory distress

  total volume of air inside decreases

  change in volume = oxygen uptake
• units of breathing rate

  breaths min-1