Gas Exchange

• Fick’s Law 


  Rate of diffusion is proportional to = (surface area x concentration gradient)/ distance molecules have to travel
• open system


  fluid flows freely over all cells
• closed system

  fluid is restricted to special vessels, allows greater control over distribution of blood
• features of insect gas exchange

  Trachea, spiracle and tracheole

  
• Opposing needs of insects

  1.Exchanging respiratory gases 2. Conservation of water
• how insects reduce water loss

  a waterproof covering (cuticle) and a small surface area to minimise the area water is lost from
• how insects perform gas exchange

  1.along a diffusion gradient in the tracheae and tracheoles 2. Ventilation by abdominal pumping
• how insects make gas exchange more efficient

  abdominal pumping
• What is needed for diffusion

  1.large surface area 2. Short diffusion distance 3. Diffusion gradient
• what does a fish gill look like

  Contains gill filaments and plate

  
• what is meant by countercurrent flow, and why is it used

  where blood and water flow across the gills in opposite directions. this means the diffusion gradient is maintained for the full length of the gill plate. As blood always passes water with a higher concentration of oxygen
• How do gills maximise surface area

  The structure of the gill plates and filaments increases surface area this increases the rate of diffusion and therefore oxygen uptake.
• Why do gills have a short diffusion distance

  they have a thin epithelium meaning oxygen diffuses across easily
• Adaptations in the lungs

  1.Increased surface area from the alveoli 2. Short diffusion distance because of one cell thick epithelium 3. Extensive capillray network maintains diffusion gradient as oxygen diffuses into blood and leaves lungs quickly
• Structure of the trachea

  flexible airway supported by c shaped rings of cartilage which holds airway open when pressure decreases . The trachea walls are made from muscle, ciliated epithelium and goblet cells
• structure of bronchi

  one in each lung, they produce mucus and contain cilia they have c rings which allow for expansion during exercise
• structure of bronchioles

  the muscle in their walls allows for bronchoconstriction meaning they can control the flow of wire in and out of the alveoli. they have cartilage to keep the airways open
• structure of alveoli

  they have collagen for strength and elastic fibres for elastic recoil this allows them to stretch for inspiration and expel for expiration
• key components of the lungs

  trachea, bronchi, bronchioles, alveoli

  
• spirometer 


  A machine used to record the volume of air breathed in and out

  
• pulmonary ventilation (dm3min-1)


  tidal volume (dm3)x ventilation rate (min-1)
• Inspiration (breathing in)

  1.the external intercostal muscles contract and the internal intercostal muscles relax 2. The ribs are pulled upwards and outwards increasing volume of the thorax 3. The diaphragm contracts and flattens increasing thorax volume 4. As thorax increases pressure in the lungs decreases 5. Atmospheric pressure is now greater than pulmonary pressure and so air is forced into the lungs