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Summary OCR A/AS-Level Biology 3.3.6 Adaptations of Plants to the Availability of Water
Revision summary of key knowledge from OCR A/AS-Level Biology 3.3.6 Adaptations of Plants to the Availability of Water.
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Adaptations of Plants tothe Availability of Water
Xerophytes
Adapted to survive in arid conditions
Waxy cuticle on leaf to reduce water lost by evaporation
Stomata on underside of leaf to reduce evaporation from direct sunlight
Stomata close at night to reduce water loss when the plant isn’t photosynthesising
Stomata close when water availability is low
Very widespread or deep roots
Low water potential inside leaves to reduce water loss – achieved by maintaining a high
salt concentration
Marram Grass:
o Rolling or curling or folding of leaves to trap air inside, preventing water loss due
to osmosis (maintains a high water potential outside leaf)
o Dense spongy mesophyll with few air spaces reducing area for evaporation
Cacti:
o Succulents – store water in their stem which becomes swollen – stems are ribbed
or fluted to allow for expansion when water is available
o Leaves reduced to spines to reduce area for evaporation and transpiration
o Stem can photosynthesise
Hydrophytes
Adapted to survive in wet conditions
Do not need to worry about water loss since water is abundant
Large air-spaces in leaves and stem keep the leaves buoyant to allow them to
photosynthesise
Stomata are on the upper side of leaves, so they are exposed to the air to allow gaseous
exchange
Specialised structures at the tip of leaves called hydathodes to release water droplets
which can evaporate since the climate is too humid for transpiration to occur
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