Plants

• How is gas exchange in plants similar to insects

  • No living cell is far from the external air, and therefore a source of oxygen and carbon dioxide
  • Diffusion takes place In the gas phase (air), which makes it more rapid than in water
• adaptions for rapid diffusion

  • Many small pores called stomata and no cell is far from a stoma and therefore diffusion pathway is short
  • Numerous interconnecting air-spaces throughout mesophyll so that gases can readily come in contact with mesophyll
  • Large surface area of mesophyll cells for rapid diffusion
  • Air spaces inside leaf have large surface area compared to volume of living tissue
• Stomata

  Minute pores that occur mainly on the leaves. each is surrounded by a pair of guard cells, which can open and close the stomatal pore. This is important as terrestrial organisms lose water by evaporation. Plants have evolved to balance the conflicting needs of gas exchange and control of water loss. they do this by closing stomata at times when water loss would be excessive
• Xerophyte 


  Plants adapted to living in areas where water is in short supply. without these adaptations these plants would become desiccated and die
• Adaptions to limit water loss

  • A thick cuticle
  • Rolling up of leaves
  • Hairy leaves
  • Stomata on pits or grooves
  • A reduced surface area to volume ratio of the leaves
• A thick cuticle 


  Although the waxy cuticle on leaves forma a waterproof barrier, water loss can still occur By this route. The thicker the cuticle, the less water can escape for example holly
• Rolling up of leaves 


  Most leaves have their stomata largely on the lower epidermis. The rolling of leaves in a way that protects the lower epidermis helps to trap a region of still air which becomes saturated with water vapour so has a very high water potential. there is no water potential gradient between inside and outside of leaf so no water loss for example marram grass
• Hairy leaves 


  A thick layer of hair on the lower epidermis traps still, moist air next to the leaf surface. the water potential gradient between the inside and outside of the leaf is reduced and therefore less water is lost by evaporation for example one type of heather plant
• stomata in pits or grooves 


  These trap still, moist air next to the leaf and reduce the water potential gradient for example pine trees
• a reduced surface area to volume ratio


  the smaller the surface area to volume ratio, the slower the rate of diffusion. having leaves that are small and roughly circular in cross section, e.g. pine needles, the rate of water loss can be reduced. this reduction in surface area is balanced against the need for a sufficient area for photosynthesis