gas exchange system.

• Gas exchange in insects


  Insects have openings in their body called spiracles that lead to air-filled tubes called trachea . The trachea that branches off into smaller tracheoles that extend into the body systems of the insect . There is a short distance between a tracheoles and an insect body cell so oxygen and carbon dioxide can directly diffuse
• Gases move in and out in three ways in insects

  • Down a diffusion gradient: As cells respire, they use up oxygen and release carbon dioxide which causes a concentration gradient to form and this causes the respiratory gases to be exchanged
  • Mass transport: Insects use rhythmic abdominal movements to push air in and out of the spiracles
  • The ends of the tracheoles are filled with water: during normal activity, this makes respiration harder but during exercise, the water leaves the tracheoles to make respiration easier which provides the insect with a ‘boost’
• Gas exchange in fish

  In fish, gas exchange occurs in the gills

  • Gills are made up of gill filaments that are thin plates covered in small structures called lamellae
  • This increases the surface area of the gills to speed up diffusion
  • The lamellae have many small capillaries and a very thin cell membrane so that there is a small distance for diffusion
  • Water follows across the gills in the opposite direction to blood so that the diffusion gradient is maintained and as much gas as possible diffuses - known as a counter-current flow
• capillaries 


  Each alveolus is surrounded by an extensive network of capillaries

  • Carbon dioxide diffuses out of the capillaries and into the alveoli to be exhaled, while oxygen diffuses the other way from alveoli and into the capillaries to be carried around the body
  • These capillaries have a diameter of around 3-4µm, which is only wide enough for one red blood cell to travel through at any one time
  • This ensures that there is sufficient time and opportunity for gas exchange to occur
• Explain how the lining of the trachea, bronchus and bronchioles provide protection against pathogens.

  Cilia beat to move mucus away from the lungs and up towards the mouth. Mucus is produced by goblet cells and acts as a barrier to pathogens from entering the ciliated epithelium. The mucus also traps bacteria and microorganisms, while blood vessels bring macrophages to engulf any pathogens in phagocytosis.
• Gills of Fish adaptations

  • Fish are adapted to directly extract oxygen from water
  • Structure of fish gills in bony fish:
  • Series of gills on each side of the head
  • Each gill arch is attached to two stacks of filaments
  • On the surface of each filament, there are rows of lamellae
  • The lamellae surface consists of a single layer of flattened cells that cover a vast network of capillaries
• Effective exchange surfaces in organisms have:

  • A large surface area
  • Short diffusion distance
  • Concentration gradient (maintained)
• Adaptations for Efficient Gas Exchange in Gills: Surface Area

  First, each gill has multiple gill arches, and extending from each of these arches is a large number of long, thin filaments.

  The more filaments that are present, the larger the surface area for diffusion

  Second, each gill filament is covered in a large number of lamellae.

  The more lamellae that are present, the larger the surface area for diffusion.
• Describe how the structure of a gill is adapted to maximise surface area, to ensure efficient gas exchange

  The gills of a fish have a large number of gill filaments and a large number of gill lamellae to maximise the surface area for diffusion
• How does counter-current flow enable efficient gas exchange in fish?

  Counter-current flow maintains steep concentration gradients for carbon dioxide (and oxygen) across the lamella
• Explain how gas exchange takes place in fish

  A steep concentration gradient of oxygen and carbon dioxide is maintained by the countercurrent flow of water and blood across the lamellae.

   

  This allows oxygen from the water to diffuse into capillaries, and carbon dioxide from capillaries to diffuse into the water
• Describe and explain the advantage of counter-current flow in gas exchange across a fish gill

  Water and blood flow in opposite directions along each gill lamella. This maintains steep (oxygen and carbon dioxide) concentration gradients along the length of each lamella
• Describe how we breathe in


  known as inspiration

  the diaphragm and external intercostal muscles contract.

  this causes the volume of the thorax to increase and the pressure in the thorax to decrease.

  As a result, air is forced into the lungs.
• Describe how we breathe out

  known as expiration

  the diaphragm relaxes and the internal intercostal muscles contract.

   this causes the volume of the thorax to decrease and the pressure in the thorax to increase.

   As a result, air is forced out of the lungs