Limiting water loss

• Limiting water loss:

  The issues for terrestrial organisms is that water easily evaporates from surface of their body and becomes dehydrated
• Insect adaptations to reduce water loss

  • Small surface area to volume ratio to minimise area over which water is lost
  • Waterproof covering over body surfaces e.g in insects covering is the rigid outer skeleton of chitin covered with waterproof cuticle
  • Spiracles are openings of the tracheae at the body surface and can be closed to prevent water loss but this conflicts with needs for oxygen so it occurs largely when the organism is at rest.
• Insects adaptations to water loss mean

  BUT these features mean that insects cannot use their body surface to diffuse respiratory gases in a way a single celled organism can. Instead they  have an internal network of tubes called tracheae that carry air containing oxygen directly to tissues.
• Limiting water loss in plants 

  • Cannot have a small surface area to volume ratio as they photosynthesise and a large surface area is required for the capturing of light and exchange of gases.

  To reduce water loss in plants terrestrial plants have waterproof covering over parts of leaf and ability to close the stoma when necessary
• What are xerophytes?

  Xerophytes are plants adapted to living in areas where water is in short supply, they evolve a range of adaptations to limit water loss through transportation. Without these adaptations plants can be desiccated and die.
• To reduce rate of water loss via evaporation organs have modifications for plants surviving in habitats with high rates of water loss and limited water supply.

  1. THICK CUTICLE


   although waxy cuticle forms a waterproof barrier, up to 10% water loss can occur via this route. Thicker cuticle = less water can escape e.g Holly
• To reduce rate of water loss via evaporation organs have modifications for plants surviving in habitats with high rates of water loss and limited water supply.

  2) ROLLING OF LEAVES

  1. protects lower epidermis from outside. Helps to trap a region of still air within the rolled leaf. This region becomes saturated with water vapour so has a very high water potential. There is no water potential gradient between the inside and outside of the leave which means there is no water loss e.g marram grass
• To reduce rate of water loss via evaporation organs have modifications for plants surviving in habitats with high rates of water loss and limited water supply.

  3) REDUCED SA:V


  having leaves that are circular in cross section (pine leaves) rather than leaves that are broad and flat, rate of water loss can be reduced, reflection is surface area is balanced against the need for sufficient area for photosynthesis to meet requirement of the plant.
• To reduce rate of water loss via evaporation organs have modifications for plants surviving in habitats with high rates of water loss and limited water supply.

  4) Hairy leaves

  1. a thick layer of hair on leaves especially on the lower epidermis, trapping still, moist air next to the leaf surface. Water potential gradient between inside and outside the leaf is reduced meaning less water lost via evaporation e.g heather plants 
• To reduce rate of water loss via evaporation organs have modifications for plants surviving in habitats with high rates of water loss and limited water supply.

  4) Stomata in pits

  1. traps still, moist air next to the leaf, reducing water potential gradient. E.g pine trees