Limiting water loss

• What needs do insects and plants have to balance?

  The opposing needs of exchanging respiratory gases with limiting water loss.
• Adaptations and their functions in insects to limit water loss:

  1. Small surface area- minimises the area over which water is lost
  2. Waterproof covering- made up of an outer skeleton of chitin covered with a waterproof cuticle
  3. Spiracles- can be closed to reduce water loss, mainly done at rest as O2 is needed more quickly during flight.
• Define xerophyte:

  A species of plant that has adaptations to survive in an environment with little water.
• What feature of leaves do all plants have to limit water loss?

  A thick waxy cuticle to stop uncontrolled evaporation and transpiration.
• Describe how rolling up of leaves limits water loss in xerophytes and give an example:

  Protects the lower epidermis (covered in stomata) from outside air. It traps a region of still humid air, meaning there is no water potential gradient therefore less transpiration will occur.

  e.g. marram grass
• Explain the function of hairs on leaves in xerophytes and give an example:

  Traps still, moist air next to the leaf surface. This decreases the water potential gradient therefore less water is lost by evaporation.

  e.g. heather plant
• Explain the function of sunken stomata in xerophytic plants:

  As they are away from the leaf surface, still, moist air is trapped next to the leaf. This reduces the water potential gradient and therefore less water is lost.
• Describe how a small surface area of leaves in xerophytes reduces water loss and give an example:

  This minimises the area over which water can diffuse out of the leaf.

  e.g. pine needles