9.5 Plant Adaptations To Water Availability Flashcards
What are xerophytes?
Plants in dry habitats that have evolved in order to live and reproduce in places where water availability is very low
General adaptations to conserve water
Waxy cuticle - reduces transpiration from the leaf surfaces
Stomata found on the underside of the leaf - can be closed to prevent water loss
Roots that grow down to the water in the soil
Xerophytes adaptations
Thick waxy cuticle Sunken stomata Reduced stomata Reduced leaves Hairy leaves Curled leaves Succulents Leaf loss Root adaptations
How do sunken stomata reduce water loss?
Reduced air movement
Produces a microclimate of still, humid, moist air which reduces WP gradient and reduces transpiration
How does a reduced number of leaves reduce water loss?
Reduced leaf area
Lower SA:V ratio which minimises the amount of water lost by transpiration
How do hairy/curled leaves reduce transpiration?
Create a microclimate of still humid air
Reduces WP gradient and minimises water loss from the surface of the leaf by transpiration
How do succulents reduce water loss?
They store water in specialised parenchyma tissue in their stems and roots
Water is stored when in plentiful supply and used in times of drought
Root adaptations of xerophytes?
Long tap roots grow deep into the ground - access water a long way below the surface
Widespread shallow roots with a large surface area to absorb any available water before it evaporates
How do xerophytes avoid low water availability problems?
Plants may lose leaves and become dormant or die completely
They can leave seeds behind to germinate and grow rapidly once rain falls again
Some survive as storage organs
Some can withstand complete dehydration and recover when it rains again
What allows some plants to withstant complete dehydration and recover from this?
The disaccharide trehalose, which allows cells to survive unharmed
What are hydrophytes?
Plants that live in water (submerged, on the surface or at the edges of bodies of water)
Adaptations of hydrophytes
Very thin/no waxy cuticle Many always open stomata on the upper surface Reduced structure to the plant Wide/flat leaves Small roots Large surface area of stems and roots under water Air sacs Aerenchyma
Why do hydrophytes have a very thin/no waxy cuticle?
Hydrophytes don’t need to conserve water, as there is plenty available so water loss by transpiration is not an issue
Why do hydrophytes have many open stomata on the upper surface?
Maximising number of stomata maximises gaseous exchange
Guard cells are usually inactive
In plants with floating leaves, stomata need to be on the upper surface of the leaf so they are in contact with the air
Why do hydrophytes have reduced structure to the plant?
Water supports the leaves and flowers, so there is no need for strong supporting structures
Why do hydrophytes have wide flat leaves?
The leaves spread across the surface of the water to capture the maximum amount of sunlight
Why do hydrophytes have small roots?
Water can diffuse directly into stem and leaf tissue so there is less need for uptake by roots
Why do hydrophytes have a large surface area of stems and roots under water?
This maximises the area for photosynthesis and for oxygen to diffuse into submerged plants
Why do hydrophytes have air sacs?
Enable leaves and flowers to float to the surface of the water
Why do hydrophytes have aerenchyma?
Aerenchyma are specialised parenchyma tissue which forms in the leaves, stems and roots of hydrophytes
It contains many air spaces formed partly by apoptosis in parenchyma
It makes the leaves and sten more buoyant
It forms a low resistance pathway for the movement of substances such as oxygen to tissues below the water
How do aerenchyma help plants to deal with low oxygen conditions?
By transporting oxygen to the tissues via a low resistance internal pathway
What are anoxic conditions?
Extreme low oxygen conditions
What happens to plants that grow in waterlogged areas?
Air is in short supply
Special aerial roots called pneumatophores grow upwards into the air
They have many lenticels which allow air to enter the woody tissue
