CIE IGCSE Biology: 复习笔记:18.1.3 Adaptive Features: Extended

CIE IGCSE Biology: 复习笔记:18.1.3 Adaptive Features: Extended

Hydrophytes & Xerophytes: Extended

Hydrophytes

  • Plants adapted to live in extremely wet conditions
  • Common adaptations include:
    • Large air spaces in their leaves to keep them close to the surface of the water where there is more light for photosynthesis
    • Small roots as they can also extract nutrients from the surrounding water through their tissues
    • Stomata usually open all the time and mainly found on the upper epidermis of the leaf where they can exchange gases much more easily with the air

     

 

Hydrophyte-adaptationsHydrophytes are adapted to live in wet conditions such as ponds

 

Xerophytes

  • Plant adapted to live in extremely dry conditions
  • Common adaptations include:
    • Thick waxy cuticle - the cuticle cuts down water loss in two ways: it acts as a barrier to evaporation and also the shiny surface reflects heat and so lowers temperature
    • Sunken stomata: stomata may be sunk in pits in the epidermis; moist air trapped here lengthens the diffusion pathway and reduces evaporation rate
    • Leaf rolled with stomata inside and an inner surface covered in hairs - traps moist air and prevents air movement across stomata which reduces transpiration
    • Small leaves: many xerophytic plants have small, needle-shaped leaves which reduce the surface area and therefore the evaporating surface
    • Extensive shallow roots allowing for the quick absorption of large quantities of water when it rains
    • Thickened leaves or stems which contain cells that store water

     

 

Xerophyte-adaptationsXerophytes are adapted to live in extremely dry conditions such as deserts

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