Adaptions for Gas Exchange in animals

• Common features of gas exchange:

  1)Surface area: volume ratio

  2) Short diffusion pathway

  3) Moist

  4) Permeable

  5) Mechanisms to maintain Concentration Gradient
• Amoeba:

  Adaption to increase Surface area - Pseudopodia

  Gas Exchange Surface- Plasma membrane with a large Surface area

  Aquatic - Moist

  unicellcular - Short diffusion pathway
• Flatworm:

  Multicellular

  Thin and flat - short diffusion pathway

  Gas exchange surface - skin - large surface area

  Aquatic - Moist and Permeable
• Earthworm:

  Large multicellular

  Gas exchange surface - the skin

  Terrestrial - moist soil and skin
• The surface area to volume ratio of an organism affects the surface adapted for use for gas exchange and the level of activity of the organism.
• As organisms increase in size, their surface area to volume ratio decreases and specialized respiratory surfaces are needed.
• Insects cannot use their external surface for gas exchange as they are covered in an impermeable cuticle to reduce water loss by evaporation.
• Fish require a specialised gas exchange surface as they have a smaller surface area to volume ratio, are relatively active and have high metabolic rates making oxygen requirements high, and require a ventilation mechanism to maintain concentration gradients for gas exchange.
• The gills of fish have gill filaments made of gill plates/lamellae, which is the gas exchange surface across which the water flows.
• Gill rakers prevent large particulates from entering and blocking the gills.
• Parallel flow:

  water and blood flow in the same direction, equilibrium is reached and oxygen diffusion reaches no net movement halfway across the gill plate.
• Counter current flow:

  water and blood flow in opposite directions across the gill plate, the concentration gradient is maintained and oxygen diffuses into the blood across the entire gill plate.
• Amphibia have aquatic tadpoles that have feathery gills, which they don’t ventilate like fish but movement of the gills through water maintains a concentration gradient.
• Ventilation in fish - taking in water

  1. Mouth opens

  2. Operculum closes (opening at back of pharynx)

  3. floor of buccal cavity lowers

  4. so volume increases, pressure decreases 5.water rushes in.
• Ventilation in humans – inspiration

  1. External intercostal muscles contract and pull the rib cage up and out.
  2. Outer pleural membrane is pulled out. This reduces pressure in the pleural cavity and the inner pleural membrane is pulled outward.
  3. This pulls on the surface of the lungs and causes an increase in the volume of the alveoli.
  4. Alveolar pressure decreases to below atmospheric pressure and air is drawn into the lungs.
• Gas exchange in insects:

  1. Pairs of spiracles on segments of the thorax and abdomen.
  2. These holes lead to tubes called tracheae leading to tracheoles.
  3. Tracheoles enter muscle cells directly. They have fluid at the end for dissolving and diffusion of oxygen.
  4. During flight, when oxygen requirements increase, fluid in tracheoles decreases to shorten diffusion path and whole-body contractions ventilate the tracheal system by speeding up air flow through spiracles.