Gas exchange in a leaf

  • Created by: Laura
  • Created on: 02-05-14 15:49
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  • Gas exchange in a leaf
    • As oxygen and carbon dioxide are produced in a plant it reduces the need to exchange with the external air
    • Structure of a plant leaf and gas exchange
      • No living cell in a plant is far from the external air and therefore a source of oxygen and carbon dioxide
      • Diffusion takes place in air which makes it more rapid than in water
      • There is a short, fast diffusion pathway. Also a plant has a very large surface area compared with its volume
      • Gas exchanges through the surface of a leaf via diffusion so no transport system is needed
        • Thin, flat shape provides a large surface area
        • Many, small pores called stomata mostly in the lower epidermis
        • Numerous interconnecting air-spaces that occur throughout the mesophyll
    • Stomata
      • Miniature pores which occur mainly, but not exclusively, on the leaves, especially the underside.
      • Each stomata is surrounded by a pair of special cells called guard cells.
      • These cells can open and close the stomatal pore. In this way they can control the rate of gaseous exchange. This is important because terrestrial organisms lose water by evaporation
      • They completely or partially close stomata at times when water loss would be excessive


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