Worksheet 3 unit 4

11th grade biology

Name:………………………………

Date:……………………………….

Respiratory System and Gas Exchange

  • Respiration: is a series of oxidation reactions taking place in all living organisms.
  • It results in the release of energy from organic compounds such as glucose.
  • Gas exchange involves the diffusion of gasses into and out of cells in order that respiration can take place.
  • Gas exchange in humans:
  • Lungs: are found in the chest, either side of the heart.
  • They are protected by the rib cage.
  • The diaphragm separates the lungs from the organs below.
  • The exchange surfaces of the lungs are the alveoli (air sacks).
  • They provide a large surface area relative to the volume of the body (about 80 m2).
  • The surfaces of the alveoli are moist for the gases to dissolve.
  • They are very thin which helps diffusion.
  • Each alveolus is surrounded by a capillary network. The blood supply helps to maintain concentration gradients.
  • Ventilation of the lungs ensures that the air in the passages is changed.

Breathing:

  • Inspiration (breathing in):
  • The external intercostals muscles contract and the internal intercostals muscles relax raising the ribs upwards and outwards.
  • The muscular diaphragm contracts and flattens.
  • Both actions increase the volume inside the thorax. Pressure inside decreases and air rushes in.
  • Expiration (breathing out):
  • The internal intercostals muscles contract and the external intercostals muscles relax.
  • This lowers the ribs downwards and inwards.
  • The diaphragm relaxes and bulges upwards.
  • Both actions decrease the volume inside the thorax to increase.
  • Air is forced out of the lungs as the elastic tissue of the alveoli recoils.
  • Pleural membranes: a double membrane that surrounds each lung. Between the two membranes there is a space called the pleural cavity which contains pleural fluid.
  • During breathing the pleural fluid acts as lubricant.
  • This allows friction-free movement of the lungs against the inner wall of the thorax.

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