exchange surfaces

• adaptations of specialised exchanged surfaces:

  = increase surface area

  • thin layers = short diffusion distance for faster diffusion
  • good blood supply = steep conc grad
  • ventilation = maintain diffusion gradient = more efficient
• trachea:

  • cartilage prevents collapsing
  • ciliated epithelium
  • goblet cells = secrete mucus to trap dust
  • cilia = move mucus along
• bronchioles contain smooth muscle allowing contraction
• inner surface of alveoli covered in solution of water, salts and lung surfactant - allows alveoli to remain inflated
• in insects, air enters via spiracles which are controlled by sphincters allowing them to open and close to minimise water loss
• tracheae of insects are lined with chitin spirals
• tracheoles are not lined with chitin so they are permeable to gases to allow gaseous exchange
• tracheole adapatations:

  • thin walls
  • highly branched
  • fluids at ends - allows oxygen to dissolve to aid diffusion and reduce water loss
  • no chitin
• process of gas exchange in plants:

  1. Air enters the tracheal system through open spiracles.
  2. Air moves into larger tracheae and diffuses into smaller tracheoles.
  3. Tracheoles branch throughout the body, transporting air directly to cells.
  4. Oxygen dissolves in water in tracheal fluid and diffuses down its concentration gradient from tracheoles into body cells.
  5. Carbon dioxide diffuses down its concentration gradient out of body cells into the tracheoles.
  6. Air is then carried back to the spiracles via the tracheae and released from the body
• concentration between tissue and air is maintained by cells using up oxygen, producing carbon dioxide and continuous ventilation
• gas exchange at higher activity in insects:

  • O2 demand builds up
  • lactic acid builds up in tissues so water potential decreases in tracheal fluid
  • water moves out of tracheoles by osmosis
  • higher surface area for gas exchange
• Mechanical active ventilation in insects

  1. Muscles around the tracheae contract and relax

  2. Changing the volume and pressure in the abdomen

  3. Squeezing the tracheae to pump air in and out of the spiracles
• Movement of tracheal fluid out into tissues

  Increases the diffusion rate and surface area for gas exchange
• Enlarged collapsible tracheae, accessory sacs, and air reservoirs in insects


  • Inflate or deflate to ventilate the tracheal system
  • Can increase the volume of air moved through the system
• Movement of wing muscles connected to sacs


  Pump air to ventilate the tracheal system
• water is more dense than air and has a much lower oxygen content = move water in one direction is simpler
• Structure of the gills:

  1. Gills are covered by an operculum flap.
  2. Gills consist of stacked filaments containing gill lamellae.
  3. Gill lamellae are surrounded by extensive blood vessels.
• countercurrent flow of blood and water creates even steep concentration gradients
• Overlapping filament tips increase resistance, slowing water flow over gills and allowing more time for gas exchange
• counter current exchange principle:

  • blood and water flow over lamellae in opposite directions
  • oxygen rich blood reaches water at most oxygen rich point maximising diffusion of oxygen to the blood
  • oxygen-poor blood returning from body tissues meets oxygen-reduced water that has had most of its oxygen removed, still allowing diffusion of oxygen into the blood.
  • This maintains a steep concentration gradient across the entire gill.
• ventilation in the buccal cavity:

  • mouth opens and lowers floor of buccal cavity increasing its volume
  • this decreases the pressure allowing water to move in to buccal cavity
  • opercular cavity expands, lowering pressure
  • floor of buccal cavity moves up increasing pressure so water flows over gills
  • water flows out of operculum
• ventilation in buccal cavity p2:

  • mouth closes, operculum opens and sides of opercular cavity move inwards
  • this increases pressure of opercular cavity and force water over gills and over operculum