3.3.6: Adaptations of plants to the availability of water Flashcards
What is a hydrophyte?
A plant adapted to living in water or where the ground is very wet.
What is a xerophyte?
A plant adapted to living in dry conditions.
What are some structural and behavioural adaptations that reduce water loss in terrestrial plants?
- Waxy cuticle prevents water loss due to evaporation through the epidermis.
- Stomata found on under-surface of leaves, reduces evaporation due to direct heating from the sun.
- Most stomata closed at night when there is no light for photosynthesis.
- Deciduous plants shed leaves in winter as less water is available (ground frozen) and the temp. is too low for photosynthesis.
Marram grass (xerophyte) lives on sand dunes, why are the conditions harsh here?
- Water in sand drains very quickly.
- Sand may be salty.
- Leaves exposed to windy conditions.
How is marram grass adapted to living in arid conditions?
leaves
- Leaf rolled longitudinally, air trapped inside, this air becomes humid, reduces water loss from the leaf.
- The leaf can roll more tightly in arid conditions.
How is marram grass adapted to living in arid conditions?
Waxy cuticle
-Thick waxy cuticle on outer side of rolled leaf, reduces evaporation.
How is marram grass adapted to living in arid conditions?
stomata
- Stomata on the inner side of rolled leaf (lower epidermis)
- Protected by enclosed air space.
- Stomata in pits in lower epidermis which is folded and covered by hairs.
- Reduces air movement and therefore loss of water vapour.
How is marram grass adapted to living in arid conditions?
spongy mesophyll
- Very dense, few air spaces.
- Less SA for evaporation of water,
How are cacti adapted to living in arid conditions?
stem
- Succulents.
- Store water in their stems.
- Ribbed or fluted stems so it can expand when water is available.
- Greem for photosynthesis
How are cacti adapted to living in arid conditions?
leaves
- Reduced to spines
- Reduces SA for evaporation (transpiration)
How are cacti adapted to living in arid conditions?
Roots
-Very widespread
Other xerophytic features?
- Closing stomata when water availability is low.
- Lower WP in leaf cells, achieved by maintaining high salt conc. in cells. This reduces WP gradient between cells and leaf air spaces, therefore, reducing evap.
- Long tap root, reach water deep underground.
What issues do hydrophytes face?
- Getting oxygen to submerged roots and keeping afloat.
- Need leaves in sunlight to photosynthesise.
Adaptations od a water lily:
- large air spaces in leaf keeps leaves afloat.
- Stomata on upper epidermis, exposed to air for gaseous exchange.
- leaf stem has many air spaces, helps with buoyancy and allows oxygen to diffuse quickly to roots for aerobic respiration.
What happens if the transpiration stream stops (e.g. if too humid)?
-Plant cannot transport mineral ions up to leaves.
