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7.06 Xerophytes

Definition:

  • Xerophytes: Plants adapted to live in environments with limited water availability.

Question

Key Adaptations of Xerophytes to Minimize Water Loss:

Rolled Leaves (e.g., Marram Grass – Ammophila arenaria):

  • Leaf Structure: Leaves roll up due to the shrinkage of hinge cells, exposing a thick waterproof cuticle on the outside.
  • Cuticle: Contains cutin, a fatty, water-resistant substance that reduces water loss.
  • Stomatal Placement: Stomata are located only on the upper epidermis, opening into the enclosed, humid area within the roll to limit water loss.
  • Hairs: Trap a layer of moist air inside the roll, decreasing the water vapor diffusion gradient, reducing transpiration.

Hinge cells in blue

Question

Reduced Leaves (e.g., Opuntia – Cactus):

  • Leaf Modification: Leaves are reduced to spines, lowering surface area and thus reducing water loss.
  • Photosynthesis Location: Flattened, water-storing stems take over photosynthesis.
  • Defense Mechanism: Spines deter animals from eating the plant, protecting water stores.

Needle-Like Leaves (e.g., Sitka Spruce):

  • Leaf Form: Needle-shaped leaves minimize surface area exposed to the air, reducing transpiration.
  • Waterproofing: Leaves are covered in a thick wax layer.
  • Sunken Stomata: Stomata are located in grooves or pits, reducing exposure to air currents and minimizing water loss.

Question

Trichomes (e.g., Phlomis italica):

  • Leaf Hairs (Trichomes): Hair-like structures on leaf surfaces trap moisture and reduce water loss, similar to the hairs on marram grass.
  • Habitat: Common in small shrubs in Mediterranean dry habitats.

Question

Succulent Stems (e.g., Euphorbia canariensis):

  • Stem Adaptation: Swollen stems store water for long-term use.
  • Photosynthesis: Stems carry out photosynthesis, reducing reliance on leaf structures.
  • Wax Coating: Thick wax layer reduces water loss by forming a barrier.

Practical Study of Xerophytes (e.g., Marram Grass – Ammophila arenaria):

  • Observation under Microscopy:
    • Use a light microscope to examine a transverse section (TS) of a marram grass leaf.
  • Low-Power Plan Drawing: Create an annotated drawing of the leaf, focusing on unique xerophytic features.
  • High-Power Detail: Draw detailed structures, including:
    • Sunken stomata at the bottom of grooves in the upper epidermis.
    • Hinge cells aiding in leaf rolling.
    • Hairs on the upper epidermis to trap moisture.
    • Thick cuticle on the lower epidermis, which lacks stomata for additional water retention.

Question

Key Terms:

  • Trichomes: Hair-like structures on the leaf surface that trap moisture and reduce evaporation.
  • Xerophyte: Plant adapted to survive in low-water environments.
  • Cuticle: Protective layer made of cutin, covering the epidermis to reduce water loss.

Practice Questions 1

Quizzes

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