IB Biology topic 6.4

• 6.4.1 Distinguish between ventilation, gas exchange and cell respiration.

  ventilation: the process of bringing fresh air into the alveoli and removing stale air.gas exchange: human must take in oxygen from their surrounding and release carbon dioxide, this process of swapping one gas with another is called gas exchange. cell respiration: the controlled release of energy in the form of ATP from organic compounds in cells.
• 6.4.2 Explain the need for a ventilation system.

  Diffusion of oxygen and carbon dioxide happens because there are concentration gradients of oxygen and carbon dioxide between the air and the blood. To maintain these concentration gradients the air in the alveoli must be refreshed frequently by the process of ventilation.
• 6.4.3 Describe the features of alveoli that adapt them to gas exchange.

  (1) Each alveolus is very small - however the lungs have many = results in a large surface area for gas exchange (2) wall of alveolus consist of a single layer of thin cells = minimum distance for diffusion (3) alveolus covered in dense network of capillaries with low oxygen/high carbon dioxide concentrations = oxygen diffuses in and carbon dioxide out (4) cells in alveolus wall secrete a fluid - keeps the inner surface moist = gases can dissolve + keeps the sides of the alveolus from sticking together.
• 6.4.4 Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli. ...............
• 6.4.5 Explain the mechanism of ventilation of the lungs in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles.

  The mechanism of ventilation: Air is exhaled into lungs via trachea - bronchi - bronchioles. Exhaled via same route. Muscles lower and raise the pressure inside the lungs to cause movement of air. Inhaling: (1) External intercostal muscles contracts - moving ribcage up and out. (2) Diaphragm contracts - becomes flatter and moves down. (3) Volume of the thorax is increased by these muscle movements. (4) Pressure inside the thorax drops below atmospheric pressure.(5) Air flows into the lungs until the pressure inside the lungs rises to atmospheric pressure. Exhaling: (1) Internal intercostal muscles contract - the ribcage moves down and in.(2) Abdominal muscle contract - pushes the diaphragm up into a dome shape.(3) Volume of the thorax decreases by these muscles movements. (4) Pressure inside the thorax rises above atmospheric pressure. (5) Air flows out of the lungs until the pressure inside the lungs falls to atmospheric pressure.