Adaptive Features

• Adaptive feature: inherited feature that helps an organism to survive and reproduce in its environment (i.e. increases its fitness)
• Fitness: the probability of an organism surviving and reproducing in the environment in which it is found
• Xerophytes: live in deserts where water is scarce and evaporation is rapid, or in windy habitats.
• Xerophytes features:

  • Deep roots to reach water underground
  • Leaves reduced spines with minimum surface area for transpiration
  • Shallow spreading roots to collect rain
  • Rolled leaves, leaf hairs and stomata sunk in pits to trap moist air
  • Waxy leaf cuticle, impermeable water
  • Stomata open at night, closed at midday when evaporation highest
  • E.g. cactus
• Hydrophytes: live in wholly or partly submerged in water.
• Hydrophytes features:

  • Leaves highly divided to create large surface area for absorption & photosynthesis
  • Very little cuticle formation
  • Lack of xylem tubes, no stomata underside of leaves
  • Stomata in the upper surface, has a thick waxy layer to repel water and to keep the stomata open and clear
  • Roots are often reduced and root hairs are often absent