Plant adaptations to water availability

• what is a xerophyte?

  plants with adaptations that enable them to survive in dry habitats or habitats where water is in short supply in the environment
• what are some examples of xerophytes?

  • cactus
  • dog rose
• what problems must xerophytes overcome?

  lack of water avilability
• how can sunken stomata help to reduce water loss?

  • high water vapour potential in air space
  • stoma at base of pits
  • water vapour collects in pit or under hairs
  • shallow diffusion gradient, reducing evaporation
  • hairs trap water vapour decreasing diffusion gradient, reducing water vapour movement out of plant
• how is leaf size an adaptation of xerophytes?

  reduced leaf surface area, water loss is greatly reduced
• how is thickness of the waxy cuticle an adaptation of xerophytes?

  • thick - to help minimise water loss from cuticle, to help survive both hot dry summers and cold winters
• how is the time the stomata open/close an adaptation of xerophytes?

  • close at hottest points of the day to reduce water vapour loss through transpiration
• how is the presence of leaf hairs an adaptation of xerophytes?

  • create a microclimate of still, humid air, reducing water vapour loss by transpiration from leaf surface
• how is waxy cuticle thickness an adaptation of hydrophytes?

  • very thin/none - don't need to conserve water as there is always plenty available so water is not an issue
• how is when the stomata open/close an adaptation of hydrophytes?

  • open at times of/all the time for gaseous exchange and guard cells are inactive
• how is the supporting structures an adaptation for hydrophytes?

  • reduced structure to the plant - water supports leaves and flowers so there is no need for strong supporting structures
• how is the leaf shape an adaptation of hydrophytes?

  • wide, flat leaves - so they can capture as much light as possible
• what is the root adaptations of hydrophytes?

  • small roots - water can diffuse directly into the stem and leaf tissue so there is less need for uptake by roots (so less roots are needed)
• how is the stem and root surface area an adaptation of hydrophytes?

  large surface area under water - maximises area for photosynthesis and for oxygen to diffuse into submerged plants
• how is air sacs an adaptation of hydrophytes?

  • some hydrophytes have air sacs to enable the leaves and/or flowers to float to the surface of the water
• how is aerenchyma an adaptation of hydrophytes?

  • specialised parenchyma packing tissue forms in leaves, stems and roots
  • has many large air spaces
  • makes leaves and stems more buoyant
  • forms a low-resistance internal pathway for the movement of substances such as oxygen to tissue bellow the water - helps plant cope with anoxic conditions in mud by transporting oxygen to tissues
• what are the problems with aerenchyma in rice?

  • provides a low resistance pathway by which methane produced by rice plants can be vented into the atmosphere
  • atmospheric methane, which contributes to the greenhouse effect and the resulting climate change