9.5 Plant Adaptations To H2O Availability Flashcards
Whats the dilemma in plants to do with photosynthesis
Land plants exist in a torn state between getting CO2 for photosynthesis and losing water they need for turgor pressure and transport.
Must have a large SA:V ratio for GE but this greatly increases risk of loss of water by transpiration.
What are Xerophytes
Plants adapted to to live on hot, dry areas are known as xerophytes.
Most plants adapt to conserve water, including:
A waxy cuticle layer to reduce transpiration from the leaf surfaces.
Stomata found mainly on underside of leaf that can be closed to prevent water loss of vapour.
However, on habitats where water is in short supply, water evaporates very quickly. Plants in frozen areas can also be xerophytes as water is not freely available to them.
Conifers are an example as well as marram grass.
What are Ways of conserving water in plants
Thick waxy cuticle (e.g. Holly plants)
Sunken stomata - located in pits which reduce air movement producing a climate of still, humid air that reduces water vapour potential gradient and so reduces transpiration.
Reduced number of stomata - reduce transpiration and gaseous exchange surfaces.
Reduced leaves - leaves of conifers are reduced to thin needles to reduce water loss.
Hairy leaves - hairy leaves trap moist air and create a climate of humidity reducing water vapour potential gradient. Marram grass even has hairs in their sunken pits.
Curled leaves - curled or rolled leaves confines all the stomata within a micro environment of still, humid air to reduce diffusion of water vapour from stomata.
Succulents- store water in specialised parenchyma tissue in their stem and roots. Often have a small swollen appearance.
Leaf loss - some plants simply shed their leaves to reduce transpiration when water isn’t available. Palo verde is an example of a plant that loses its leaves. The trunk and branches turn green and photosynthesise with minimal water loss to keep it alive.
