a)State the characteristics of respiratory surfaces. [4 m] b) Describe the mechanism of inhalation and exhalation in mammals

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a)State the characteristics of respiratory surfaces. [4 m]

  • Highly vascularised / Network of blood capillaries
  • Large surface area (for gaseous exchange)
  • Thin membranes / epithelium / one cell thick wall;
  • Moist lining
(4 Marks)
 Breathing in

  • External intercostal muscles contract, 
  • intercostal muscles relax; lifting / 
  • The rib cage rises upwards and outwards, 
  • Muscles of diaphragm contract; hence if flattens; 
  • The volume of the thoracic cavity increases, 
  • The air pressure in the thoracic cavity decreases, 
  • Higher air pressure in the atmosphere forces air into the lungs (through the nose)
(8 Marks)
Breathing out

  • External intercostal muscles relax; 
  • Internal intercostal muscles contract; 
  • Moving the rib cage downwards and inwards, 
  • The muscles of diaphragm relax, hence the diaphragm assumes dome shape; 
  • The thoracic cavity decreases; 
  • While pressure increases; 
  • Higher pressure forces air out of the lungs (through the nose)

(8 marks)
Maximum 20 Marks)

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