Aims of the session:
Take measurements of leaves + see if xerophytes have a different pattern of mass loss
Learn about the adaptations xerophytes have
See what type of question they can ask about xerophytes (and be able to answer it)
Plants in different habitats possess different adaptations:
Mesophytes: plants adapted to a habitat with adequate water
Xerophytes: plants adapted to a dry habitat
Halophytes: plants adapted to a salty habitat
Hydrophytes: plants adapted to a freshwater habitat
Leaf undersurface of the tree fern. Extremely high number of stomata per unit in a species living in tropic cloud forests where is is very moist.
Stomata sunken in pits creates local humidity/decreases exposure to air currents;
Presence of hairs creates local humidity next to leaf/decreases exposure to air currents by reducing flow around stomata;
Thick waxy cuticle makes more waterproof impermeable to water;
Xerophytes possess some or all of these adaptations to prevent excessive water loss
Xerophytes possess some or all of these adaptations to prevent excessive water loss cont.
Stomata on inside of rolled leaf creates local humidity/decreases exposure to air currents because water vapour evaporates into air space rather than atmosphere e.g. British Marram grass
Fewer stomata decreases transpiration as this is where water is lost;
Xerophyte adaptations summary:
Left and right Epidermis of the cactus Rhipsalis dissimilis.
Left: View of the epidermis surface. The crater-shaped depressions with a guard cell each at their base can be seen.
Right: X-section through the epidermis & underlying tissues. The guard cells are countersunk, the cuticle is thickened. These are classic xerophyte adaptations.
Transverse Section Through Leaf of Xerophytic Plant