Gas Exchange and Exchange of Substances

  • Created by: India.02
  • Created on: 11-05-19 19:39
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  • Gas Exchange
    • Lungs
      • Transfer oxygen to the blood and to remove waste CO2
      • Contains millions of little air sacs called alveoli - where gas exchange takes place
      • Alveoli have an enormous surface area - 75m*2 in humans - they also have a moist lining for dissolving gases, very thin walls and a good blood supply
    • Villi
      • Small projections inside the small intestine - increase surface area in a big way so that digested food is absorbed much quicker into the blood
      • They have a single layer of surface cells and a very good blood supply to assist quick absorption
    • Leaves
      • Carbon dioxide diffuses into the air spaces within the leaf, then it diffuses into the cells - where photosynthesis happens
      • Underneath of the the leaf is the exchange surface - covered in small holes called stomata which the CO2 diffuses through
      • Oxygen and water vapour also diffuse out through the stomata - water vapour lost from all over the surface but mainly through stomata
        • Water vapour evaporates from cells inside the leaf and escapes by diffusion - higher concentration inside the leaf than outside
      • Size of stomata controlled by guard cells - close stomata if plant is losing water faster than it is being replaced by the roots - without guard cells the plant would wilt
      • Flattened shape of leaf increases area of exchange surface so that it is more effective
      • Walls of the cells inside the leaf forma another exchange surface - air spaces inside the leaf increase the area of this surface so there is more chance for CO2 to get into cells
    • Gills
      • Water (containing oxygen) enters the fish through its mouth and passes out through the gills - oxygen diffuses from the water into the blood in the gills and CO2 diffuses from the blood into he water
      • Each gill is made of thin plates called gill filaments - big surface area for exchange of gases
        • Filaments covered in tiny structures called lamellae - increase surface area more
      • Lamellae have lots of blood capillaries to speed up diffusion - thin surface layer of cells to minimise the distance that the gases have to travel
      • Blood flows through lamellae in one direction and the water flow over in the opposite direction - maintains large concentrationgradienj between water and blood
      • Concentration of oxygen in the water is always higher than that in the blood - as much oxygen diffuses from the water into the blood


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