Plants

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  • Classifying Plants
    • Hydrophytes
      • Grow submerged or partially submerged in water
        • E.g. water lily, which is rooted to the mud at the bottom of a pond and has floating leaves on the surface of the water
      • Hydrophytes are adapted in the following way;
        • Stomata on the upper surface of leaves
        • Leaves have little cuticle
        • Large air spaces in stem and leaf tissue providing buoyancy
        • Water supports the plant, so little lignified plant tissue is needed
        • Poorly developed xylem as they are surrounded by water so do not need transport tissues
    • Mesophytes
      • Grow well with an adequate water supply, but in prolonged dry periods they survive by;
        • Shedding their leaves to reduce transpiration
        • Producing dormant seeds
        • Bulbs or other organs surviving underground
    • Xerophytes
      • A xerophyte is a plant that lives where water is in short supply e.g. hot deserts
      • It has structural adaptations which reduce water loss mainly by reducing the rate of transpiration
    • Marram Grass
      • Colonises sand dunes
      • Thick cuticle on leaves - reduces water loss
      • Stomata in pits - Water vapour not moved, therefore maintains humid air around stomata, therefore reduces water potential gradient and rate of diffusion of water
      • Hairs surrounding stomata - traps water molecules, therefore maintains humid air around stomata, therefore reduces water potential gradient
      • Hinge cells - Causes leaves to roll up, this maintains humid air around stomata, reducing water potential gradient and reduced surface area of the leaf

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