BIOLOGY - CHAPTER 7

BIOLOGY - CHAPTER 7

1. Specialised exchange surfaces

   • Single cell organisms - exchange gases by diffusion through cell surface.
     • Because: low metabolic activity, large SA:V ratio.
   • Large surface area
     • Overcomes limitations of lower SA:V ratio.
   • Thin layers
     • Short diffusion distance increases rate (alveoli).
   • Good blood supply
     • Maintains steep conc. gradient (fish gills).

2. Human gaseous exchange

   • Nasal cavity
     • Large SA & blood supply (warms air), hairy mucus secreting lining (traps pathogens) and moist surfaces (reduces evaporation.
   • Trachea
     • Supported by incomplete cartilage rings, lined with ciliated epithelium (inc. goblet cells). Cilia move mucus w/ trapped dirt/pathogens away from lungs, most is swallowed.
   • Bronchus
     • Trachea divides into left and right bronchus leading to each lung. Essentially smaller trachea.
   • Bronchioles
     • Bronchi divide into small bronchioles. No cartilage rings, have smooth muscle in walls which allows them to constrict/dilate & control volume of air reaching lungs. Flattened epithelium => some gaseous exchange.
   • Alveoli
     • 'Air sacs', 200-300µm diameter, composed of flattened epithelial cells, collagen and elastic fibres. Elastic recoil helps squeeze air out. Lung surfactant prevents collapse.

3. Components of lung volume

   • Tidal volume
     • Volume of air that moves in and out of lungs with each resting breath.
   • Vital capacity
     • Strongest exhalation followed by deepest intake of breath.
   • Inspiratory reserve volume
     • Maximum volume of air you can breathe in over and above normal inhalation.
   • Expiratory reserve volume
     • Extra volume of air that can be forced out of lungs over and above normal exhalation.
   • Residual volume
     • Volume of air left in lungs after strongest exhalation.

4. Insect gaseous exchange

   • The tracheal system is a series of tubes that supply muscles with oxygen directly.
   • Pumping of the abdomen ventilates the body.
   • Spiracles open and close to control the extent of gas exchange.

5. Bony fish gaseous exchange

   • Counter-current gas exchange
     • Gills are composed of gill filaments (primary lamellae) = large SA for gas exchange. Gill plates (secondary lamellae) increase SA more.
     • Many capillaries and a thin surface layer of cells in gill plates => increase rate of diffusion.
     • Blood flows through gill plates in opposite direction to water, maintaining high conc. gradient.
     • Tips of gill filaments overlap, increasing resistance to water and allowing more time for gas exchange.
   • Fish gills ventilation
     • 1. Fish opens mouth, lowering floor of buccal cavity => increased volume, decreased pressure inside cavity so water is forced in.
     • 2. Fish closes mouth, floor of buccal cavity raised => volume decreases, pressure increases so water is forced out across gill filaments.
     • 3. Increase in pressure forces operculum open, allowing water to leave gills.